Fake Defector

Garak: I'm glad to see the plan is going as scheduled.
Jem'Hadar Soldier: What plan is that?

Garak: You mean no-one told you? You see, I pretend to be their friend... and then I shoot you.

—Star Trek: Deep Space Nine

Every so often, a hero (usually a police officer or spy) will pretend to go to The Dark Side in order to reach the Big Bad. This is not the same as The Infiltration; in this case, the hero keeps his true identity, but convinces the bad guys that his loyalties have switched. Frequently many of the good guys end up believing it too.

The hero will often have to persuade the bad guys of his authenticity by attacking one of his 'old' comrades or doing something else evil. Another frequent tactic is for the hero not to contact the bad guys, but instead just arrange for his life to fall apart—get fired from his job, start to drink, and so on—and wait for his enemies to contact him.

The audience is usually told in advance that the hero is doing this, but occasionally they are not. Often it is subject to a sort of Unspoken Plan Guarantee: if the audience knows, the bad guys are more likely to know as well.

Compare the inverse, the Heel Face Mole.

As a betrayal trope many examples will contain spoilers.

Examples of Fake Defector include:

Anime

In the Grand Finale of Sailor Moon, Sailor Uranus and Sailor Neptune do this, and even kill Pluto and Saturn in order to gain Sailor Galaxia's trust. Of course, as it turns out, they only did it because the Applied Phlebotinum handed out to Galaxia's henchmen was the only weapon that could defeat her. Or so it seemed.
- This scene often appears in the Sera Myu, or stage musicals, and even has its own song.
- In an earlier arc, Sailor Moon herself feigned a falling out with the other senshi and attempted to join the Dark Kingdom so she could find the entrance to the Dark Kingdom. Pity she tried this on the most cunning of the Dark Kingdom's servants...
Digimon Savers: Kurata rolls out the red carpet Touma to do this. Touma goes so far as to get into a fistfight with Masaru and nearly kills Ikuto and Yatagaramon.
Nancy does this with Yomiko in the Read or Die OAV, while quoting "to deceive your enemy, first you must deceive your friend".
Mirage pulls one of these in Transformers: Robots in Disguise. After having a genuine fight with his team, he realizes that the Predacons have been listening in and promptly takes advantage of the situation to pretend that he wants to defect.
Chie pulls this off in Mai-Otome by pretending to side with the Valkyries as part of two separate plans:

1. To wrest them and any other Otomes who may have sided with Nagi from his control, and
2. To knock Tomoe off her high horse, knowing fully well that she would take the first opportunity to sell them all out. The first part succeeds easily, but the second? Not so much, as Tomoe is too stubborn to be swayed into a Heel Face Turn, and snaps instead.

Gajeel was revealed to be one of these for the Fairy Tail guild.
Conrad pulls one of these in Kyo Kara Maoh.
- The event reshapes the entire series and leads to huge amounts of character development—you can pretty much divide the series into 'before' and 'after' this arc, with a brief transition period between his disappearance and his reemergence as Belial's new Dragon.
- The audience is not let in on the arrangement, nor is any other living hero. We are given blatant foreshadowing of the apparent Face Heel Turn about three minutes before The Reveal.
  - Conrad wears a similar coat and has a similar scene in the same arena in season three, and you can see Yuuri's stomach turn over as he says half-jokingly 'not this again.' Conrad reassures him. Then he declares his own bid for the Shimaron throne on the strength of an unbroken family line that lost power four hundred years ago. Certainly messes with everyone's plans.
- The fact that they still have Conrad's severed left arm in its original sleeve while he's walking around with two working arms is a big tip-off that something more convoluted happened than just the most loyal person ever deciding to betray his king, or even Brainwashed and Crazy. It's basically 'cause God Is Evil. Or..possessed by evil. Basically God is playing Xanatos Speed Chess with himself, without anyone else suspecting there's more than one will nudging the pieces. Yuuri is the culmination of the good and evil plots, because there's no way either of them would have succeeded in getting there if they hadn't built on the other's foundations for their own purposes. You Can't Fight Fate and yet he very much has a choice and control.
In Naruto, Itachi is claimed to have been one after he died, though it wasn't something anyone else planned, but a way to fulfill his mission without killing his brother.
- It's also possible Danzou did plan this and had some measure of control over his nuke-nin, although the fact that he didn't act to keep Sasuke from leaving the village indicates that he didn't feel he needed him on hand for continuous leverage.
  - Supposedly the poor bastard remained loyal the whole time, on his own. Secretly.
  - His Fake Defector status makes the sequence where he was introduced make more sense, really. He did put Kakashi in the hospital, but declined to actually hurt anyone, otherwise, when it would have made sense, and left without attempting to secure Naruto. Not appearing to give a damn about anything covereth a multitude of mercies.
- The way his farewell speech was set up, it was almost certainly a deal he cut with his boss: as long as he makes sure the kid never suspects what really happened, he'll be left alive. Definitely, the Fake Defector thing was the official plan—the whole point was supposedly that if the Konoha authorities put down the rebellion, even by a similar massacre, it would be a political blow and might cause a war, but if another genius went insane and did something heinous, well, that's just another day in the shinobi lifestyle.
  - Danzou's motivations here are suspect. Especially with the gratuitous child-and-civilian killing thing. Much better suited to acting out his grudge against the clan than any rational plot. Which Itachi should have known.
  - Which is why some parties think Sasuke was probably a hostage/bribe, as discussed above.
In the X/1999 anime, Arashi joins the Dragons of Earth to save Sorata from sacrificing himself for her. When Fuuma gives him an order to kill him though, she betrays him.
In Dragon Ball GT, Gill appears to betray the team to the machine mutants. Only Trunks is in on the plan.
- In the Garlic Jr. Saga of Dragonball Z, Piccolo did a variation of faking defection to Garlic Jr: He ended up being bitten by one of the Black Water Mist-infected characters, and then faked infection himself and fought Gohan and Krillin ruthlessly in order to get close enough to Garlic Jr. and then free Kami and Mr. Popo. He only let Krillin in on the plan when he was "biting" him on the neck, resulting in Krillin faking defection as well.
In the The Legend of Zelda Four Swords Plus manga, the Violet Link pulled this off in order to learn of the enemy's plans, even knocking out the Green Link in order to prove his "loyalty".
Lelouch, along with Suzaku from Code Geass pull this off at the end of the series. They pretend to become the new villains who take over the world, but it turns out Lelouch had planned his own death to bring world peace.
Yukimura pulls one in Samurai Deeper Kyo.
Soul Eater in the first episode of Soul Eater. It's hard to tell if Maka was in on it, but if so, she's quite the actor.
Bleach: Byakuya does a pretty good one in the Zanpakuto arc. The ally he has to kill is his sister Rukia's Zanpakuto, Sodeno Shirayuki, and he does it without flinching (of course).
It is implied in the beginning of the Manaphy movie that Jack Walker had to pull off a fake defection in order to get close to Phantom and retrieve Manaphy's egg to prevent him from accessing the Samiyan Sea Temple.
Hinata from Bloody Cross. At first it looks like he's a traitor who tried to kill Tsukimiya and sided with Arcana, but it turns out he's a fake defector who's still working for Tsuduki.

Comic Books

Nightwing becomes a fake defector in the year following the Infinite Crisis storyline. This was done to give him additional credibility among several rival gangs. His success is debatable; on one hand Slade asks him to train his daughter Rose as the new Ravager, but on the other hand, his actions lead to an encounter with Superman. Revealing both Slade's insight and foresight, Slade prepares a gizmo to give Nightwing's heartbeat the sound of a truthful man rather than a liar.
- Slade gave him vicoden?
Post Badass Decay, Juggernaut (an X-Man at the time) is ordered to fake-defect to gain intel on the New Bastards on the Block. Unfortunately, Juggernaut's kindred-spirit Squid Boy was not in the loop and, getting caught in the crossfire during a battle, tells Juggernaut he'll never forgive him before promptly expiring. Ouch.
The Trickster and the Pied Piper attempted to infiltrate their old friends, the Flash's Rogues Gallery—an apparent reversal of their Heel Face Turns. When they appeared to have been complicit in the murder of Bart Allen, the Flash, they found it impossible to convince people of their sincerity.
Star Wars: Dark Empire had Luke Skywalker falling to the Dark Side, if only to try to bring it down from within.
The Squadron Supreme limited series sees the entire team pretending to be brainwashed into joining the Institute of Evil.
The first story arc of Ultimate X-Men has Cyclops storming off and joining Magneto's Brotherhood of Mutants. Guess why he does it.

Fanfic

In Winter War, Hisagi apparently defected to Aizen during the Fake Karakura Town battle when it became obvious that he was going to win. He did so at Yamamoto's orders... but with Yamamoto and everyone else who was in on it dead, La Résistance believes he defected for real. Even when he contacts them and offers to help them invade Hueco Mundo, they have no way of knowing if he's genuinely on their side... and neither does the reader, until we get a chapter in his POV a while later.
Zecora in Fallout Equestria. Tragically, her plan to assassinate the Zebra Caesar might have worked if she hadn't ran into Applesnack during her 'escape'. He beat her to death.

Film

There's an example of a reverse of this trope in The Living Daylights in which Koskov pretends to defect to the West. Turns out he's playing both sides against the middle and used the defection as an opportunity to get his girlfriend offed by James Bond (who doesn't actually do it and ends up taking off her clothes later in the movie).
Happens in Greenmantle (1916), a Richard Hannay novel by John Buchan.
Data in Star Trek: First Contact.
Miller's Crossing revolves around this trope.
Kyra joining the Necromongers in The Chronicles of Riddick.
In X Men First Class, Darwin does this to Sebastian Shaw's group of evil mutants as a ploy to give his teammate Havok a clear shot at Shaw's group (Darwin's own mutant ability will protect him from Havok's attack, and their friend but genuine traitor Angel, who wouldn't be safe otherwise). It doesn't turn out so good for Darwin when Shaw's group survives unscathed due to Shaw's mutant ability allowing him to absorb Havok's attack.
Interestingly done in The Prestige. Angier sends his assistant, Olivia to work for Borden and feed him information. Knowing Borden would be suspicious, he tells her to admit that Angier sent her as a spy, but to claim that she was so mad at Angier for treating her like a pawn that she's willing to feed him information about Angier. In other words, the whole plan is completely transparent, both sides know full well she's working as a double agent, but neither can be sure whether she's a defector or a fake defector.
In The Godfather, Don Corleone send Luca Brasi to infiltrate the gang of Sollozzo to garner information, but Sollozzo is wise to the plot, and Luca ends up sleeping with the fishes.

Literature

In A Song of Ice and Fire, the beyond honorable Jon Snow becomes a fake defector in order to spy on the wildling king Mance Rayder; he is forced to kill Qhorin Halfhand in order to gain their trust. And then to have sex with his new wildling girlfriend every night to maintain their trust. I mean, how else to convince them he's forsworn those vows of chastity he loves so much?
- Hey, to be fair he does feel pretty bad about it! ... for about a chapter...
- The Westerling family counts as well. The family is of minor nobility and are sworn to the Lannisters. After their daughter Jeyne, likely the only family member who doesn't fit this trope, marries King Robb Stark, leader of one of the armies opposed to the Lannisters in the War of Five Kings, they pretend to declare loyalty to the Starks. However, Robb's direwolf Grey Wind, an Evil-Detecting Dog, indicates that something is wrong about the family. Later, Jeyne's mother reveals to Jaime Lanniester that she had been in contact with his father, the head of the Lannister family, and was aware of the planned betrayal of Robb Stark at the hands of one of his sworn families. She also gave her daughter drugs to prevent conception, thus ensuring the male line of the Stark family died with Robb (or so she thought).
  - Wyman Manderly, ever loyal to the Starks, who pretends to defer to the Freys and Boltons when it's really all a ruse to dish up some revenge of his own.
Fiona Samson in the Bernard Samson Series, who was playing this for a seriously long time.
John Le Carre novels use this a lot - with large amounts of detail on how you go about doing this (slowly dropping out of society, becoming a drunk, etc).
Successfully pulled by Sir Horace Harkness in the Honor Harrington series, when their ship was taken by Havenite State Sec. A life of smuggling and bootlegging certainly paid off—he managed to deceive his watchdogs, hack the enemy ship's central computer, free his mates, and blow the entire ship to Kingdom Come after making a clean getaway. He was deservingly knighted for this performance.
Professor Severus Snape of the Harry Potter series. Interestingly, he defected to both sides at different points, so we're kept guessing for most of the series about which side he's a fake defector to. (Fans debated it to hell and back.) It all ends with a very unusual twist: his deception is successful but his mission fails. Voldemort believes Snape, but kills him anyway, out of expediency. That said, he was able to prevent a whole lot of worse abuse towards the students of Hogwarts using his position as Headmaster, and was able to give Harry his all-important memories about Voldemort's extra Horcrux, so in a way he succeeded.
Subverted in Emperor: The Gods of War by Conn Iggulden, where Brutus actually has done a face-heel turn and betrayed Caesar. However Caesar and his generals play it out as a fake defector, and even Brutus himself does so in order to get into Caesar's daughter's bed.
In Watership Down Bigwig tells the Efrafans that he's a member of the Owsla who escaped the destruction of his warren by Men, which is true except Bigwig neglects to mention that he's part of a group of similar refugees hoping to spring some of the Efrafan does for their own warren.
Lara of the X-Wing series started off as a bad guy playing The Mole in the New Republic. She caused the near-total destruction of an X-wing squadron, then went back to the Imperials, got disgusted by her newest boss's insistence that We Have Reserves, and engineered his death. Then, awaiting another chance, she went undercover among the New Republic again, joined an X-wing squadron, and started Becoming the Mask and finding that Good Feels Good, so she switched sides and started getting close with the only survivor of the X-wing squadron she'd destroyed. Then her true origin was revealed and she was forced to flee and rejoin the bad guys as a Fake Defector, contributing to a major New Republic victory. It ends on a bittersweet note, and it's definitely implied that things become happier.
In Orson Scott Card's novel Shadow Puppets, Suriyawong spends most of his time working his way up to being the Big Bad's second-hand man so that when the time comes he can give the good guys a chance to shoot the Big Bad in the head.
In Tim Powers's novel Declare his protagonist Andrew Hale is more or less shoved into making a false defection in order to get close to his nemesis Kim Philby.
In Sandy Mitchell's Warhammer 40,000 Scourge the Heretic, when they are infiltrating a smuggling operation, Kyrlock claims to have deserted the Imperial Guard and need to escape. Later, when their guide attempts to rape a girl also waiting to be smuggled, and Elyra is unable to get him to back down, Kyrlock tells him that while Elyra doesn't want to share, he would be willing. This lets him get close enough to bring the man down. Though it is over in a couple of minutes, Elyra is nearly convinced that he means it; when he says he knew she would back him up, she is embarrassed and can not admit how close it came.
Happens many times in Romance of the Three Kingdoms. Especially noteworthy is just before the battle of Chi Bi. Cao Cao's Fake Defectors are easily discovered, and used to plant false defectors to defeat Cao's giant navy.
Also common in Kamakura-era retellings of the Tale of Genji. Many scenes in Genji make it clear that Genji was having an affair with the Emperor's chief wife, and even fathered her child. To avoid the unpatriotic implications, the retellings would have them go through the same conversations... but later reveal they were faking the whole thing to fool their enemies! And then NINJAS ATTACK!
As of The Gathering Storm, Verin is revealed to be one of these, having joined the Black Ajah to save herself, then studied it and eventually brought it down from within. Considering how well she fooled her fellow Blacks, and the Loophole Abuse she used to be able to divulge all (which also entailed a Heroic Sacrifice),it's tempting to call her a Magnificent Bitch despite still being one of the Heroes. She's certainly mistress of The Plan.
Briefly done by Ax, of all ~~people~~ Andalites, in Animorphs. It was a spur-of-the-moment idea, and he only stuck with it long enough to get into a better position to fight back.
In Tom Clancy's Cardinal of the Kremlin, Jack Ryan pulls this, staging several 'incidents' to trick the Russians into trying to recruit him, including a rather public incident involving a gay senator. He's not actually going undercover, though—he just needs to arrange a one-on-one with the KGB Chief, so he can blackmail HIM into defecting... regardless, the whole thing goes off without a hitch.
In the Star Trek Double Helix novel "Double Or Nothing", Mackenzie Calhoun needs to infiltrate the Big Bad, so he punches out an admiral. (He was supposed to have a loud argument with him, but he decided that he needed to be punched...to make the charade more authentic, of course). It is subverted, however, in that the Big Bad sees right through it and keeps it hidden until the big moment.
The female lead of the James Bond novel and film From Russia with Love was told that her mission was to become one of these to leak false intelligence to the West. Her mission is actually a set up to lure Bond into a situation where SMERSH/SPECTRE (Depending on the adaptation) can kill both of them in a manner that embarrasses the British government.

Live Action TV

Wolf of The Tenth Kingdom is a particularly well-done version of this trope. This editor was guessing, even right up to the very end, which side he would truly turn out to be on. It helps that, as a deconstruction of many fairy tale tropes, Happy Ever After was not guaranteed by any means, and the ending still remains rather dark...
Spock did this in Star Trek: The Original Series to help Kirk steal a Romulan cloaking device.
- It was done again in The Next Generation by Wil Riker AND Picard, who basically had to act like they didn't know each other and would happily kill one another.
- In another episode of The Next Generation, a Romulan officer falsely claims to be a middle-ranking clerk of negligible importance who had come across some important information about a secret base which the Romulans planned to launch an attack on the Federation from. His defection was sincere, but he was lying about his identity. He wanted to warn the Federation about the attack so a war could be prevented, but he did not want to further betray his homeworld. He finally admits that he is an Admiral and agrees to hand over any required information to the Federation. Tragically, it turns out that he is the Unwitting Pawn, fed false information by Commander Tomalak to lure the Enterprise into crossing into the Neutral Zone first so they could ambush them and justify an invasion of the Federation. Fortunately, Captain Picard arranged ahead of time for the Klingons to sneak in with them in case they needed rescuing. Both sides retreat without a war starting.
Jack Bauer in 24 series 3, breaking out Ramon Salazar from prison was an elaborate sting operation. In order to convince the Salazars that he had gone to the bad side, he had to point an (unloaded) pistol at Chase's head and pull the trigger. He is assisted by Gael Ortega, who goes so deep undercover as a mole that CTU arrests and interrogates him before realizing their mistake.
- This is in addition to the cocaine habit he starts in the same season to convince Salazar of his defection. Proving once again that Jack Bauer is a badass.
  - Done again by both Tony Almeda and Jack in the season 7. Also Ryan Seaton fakes a bad-to-good defection.
Jack Bristow in Alias, pretending to leave the CIA to work for SD-6.
Gary Best in The Bill, whose undercover assignment involved faking his sacking for assault. Adam Okaro and Lewis Hardy also did this. The latter shot to miss Roger Valentine.
Mission: Impossible had at least one such episode, if not more.
Miami Vice had one of these as well.
The abrupt Series Finale of Angel involved a similar device.
- In an earlier episode, Angel Neck Snaped his teammate (who was part demon and able to survive such an attack) to get a Nazi-like team to accept him so he could figure out their plans.
In an episode of Get Smart, Max is "fired" from CONTROL and becomes a drunk, all part of a scheme to get him approached by KAOS so he can learn their latest evil plan.
- It turns out to be somewhat pointless, as it turned out that the KAOS unit was long defunct, and being run by inflitrators from various government agencies.
Law and Order: Criminal Intent has an episode where Goren is forced on leave and ends up working with some bad cops, and his partner nearly shoots him. Yeah, it was all planned by Goren and the captain.
On Buffy the Vampire Slayer, in the episode "Enemies," Angel pretends to have turned into his evil alter ego Angelus. Buffy is in on the plan, but the audience doesn't find out until the moment when Angel reveals himself.
In several episodes of the second season of Star Trek: Voyager, Tom Paris becomes sullen and insubordinate so his fake defection (part of a mission to root out an informant) looks real.
- He goes as far as setting up a gambling ring and skimming from the betting pool to increase the appearance of an unreliable, unethical officer.
Battlestar Galactica: In order to get to her daughter on board a Cylon Baseship, Athena tells Caprica Six that she thinks that Hera is safer there.
- Boomer does that too. Ellen thinks that Boomer helped them escape. Boomer only pretended so to get access to Galactica and steal Hera.
Stargate SG-1: In the episode "Shades of Grey", Colonel O'Neill gets suspended from duty for stealing technology from aliens. This allows him to infiltrate a group of bad guys, but in the process he alienates his team, who are quite shocked at his behaviour (not being in on the plan). Of course, they're all friends again by the next episode.
- Interesting thing is that in that episode Daniel appears to have a friendly talk to Jack at the end, and reveals he came because he lost the draw.
- Teal'c fools Ba'al into believing he was brainwashed in "Stronghold".
- Carter also had to pretend to be infected by a Goa'uld symbiote clone among an entire town infected by them to trick them into being arrested by the SGC. In order to sell the deception, she also had to hit one of her allies beforehand.
Mason Drake in Lois and Clark. Immediately after Lois and Clark agree to share their information with her (against Lois' judgment), she's sharing it with Intergang's The Dragon. Immediately after that, though, it turns out this is part of Lois' plan to make him incriminate himself on tape.
The opening quote of this article, from Star Trek: Deep Space Nine, turned out to be in a holodeck scenario. But the scene was such a perfect fit to Garak's devious personality that most fans forget he didn't really do it.
In Crime Story, the lawyer for the Federal task force that is trying to take down Big Bad Ray Luca, pretends to be drunk and gets kicked out of the agency, so that he can become Luca's lawyer, and then inform the task force about everything Luca is doing. However, Luca points out to one of his henchmen who questions whether the lawyer would be loyal to Luca, that even if this lawyer was pretending to go to his side, because of lawyer-client confidentiality rules, nothing he tells the feds can be used against him.
Bo pretended to be a dirty cop for a while on Days of Our Lives.
In the Lost episode "The Economist," we see Hurley questioning Locke's leadership. In his next scene, he tells Sayid and Kate that he has abandoned Locke's group. It turns out to be a ruse, to which the audience was kept in the dark.
- Also, Benjamin Linus pulls this in "What They Died For", even going as far as to kill Charles Widmore (though that part probably wasn't an act) to convince the Man in Black where his loyalties lie. Oddly enough, he doesn't actually accomplish much, other than to allow Miles and Richard to escape the Man in Black's wrath and eventually get off the island.
Sgt. Miller pretended to collaborate with a criminal gang in an episode of Heartbeat, though the writers didn't even try to explain why he didn't tell the other police what was going on.
Hiro from Heroes pretends to stab Ando with a katana in order to join the other side.
In the Pushing Daisies episode "The Norwegians", Olive resents the fact that she is perpetually Locked Out of the Loop and decides to join the Norwegian detective team that is trying to put Emerson out of business and would have exposed Ned in the process. It's revealed that she was faking all along in order to throw them off the track.
In the Sentai show Kousoku Sentai Turboranger Pink Turbo winds up joining the bad guys in attempt to recover an antidote for the poisoned Blue Turbo by fighting alongside the monster of the week and "accidentally" getting poisoned by it as well forcing it to give her the antidote. Oddly enough this didn't seem to be planned in advance at all, she just happened to take a hit to her head during a battle and decided to fake memory loss to join the bad guys. The other guys had no idea what she was doing until the Reveal when Blue was shown to be healed. She even was perfectly willing to shoot a machine gun at them as part of her plan.
- Chouriki Sentai Ohranger repeated this plot only this time had it fail. Ohyellow joins the bad guys in attempt to recover an antidote however unlike Pink Turbo faking amnesia Ohyellow faked cowardice and surrendered instead. Ohyellow also lets herself get hit by the poison darts and tries to get the antidote however she wore a bulletproof vest to protect herself unlike Pink Turbo who allowed herself to be poisoned. Since Ohyellow doesn't take as many risks the bad guys aren't fooled and give her a fake antidote instead. They then need to use a backup plan instead.
- A not-so-much copy-paste-from-Turborangers Fake Defector plot is also shown in Choujin Sentai Jetman, the 'fake defector' none other than Red Hawk himself, pretending to join the bad guys so they will return his girlfriend-turned-evil. Turns out he was trying to sneak into their base and destroy their mean to transport themselves into the real world. Plan failed, but in the end, their chief praised him and his teammates for being powerful and cunning enough to break through the enemy's defenses.
- Happens again in Bakuryuu Sentai Abaranger; Maharo (who was a dragon for the villians before her Heel Face Turn) makes a deal with Abarekiller and rejoins the villians with all of her former power restored. The heroes quickly learn that this is all part of her plan to A) free Asuka from the dark armor and B) get close to the Big Bad and wait for a chance to strike. The first half of her plan goes smoothly, but not the second half.
- Kaizoku Sentai Gokaiger has Luka attempt this to free herself, Joe, Don and Ahim in episode 16... and it fails right off the bat, because Basco, the one who had kidnapped them, didn't buy it for a second.
- And in the other hemisphere, Power Rangers Operation Overdrive involves a Fake Defector plot when the Rangers need to acquire a Houou statute from a villain faction.
Done in The Unit, which takes it pretty far... Sam McBride, to find Big Bad Leon Drake, "attempts" to rape Bridget Sullivan (who isn't in on this), engages in a shootout and kidnaps Molly Blaine. The result of this is Molly separating from Jonas and Jonas telling Colonel Ryan that he's no longer fit for command, to which Ryan eventually agrees, taking a promotion.
It is revealed late in season 4 of Farscape that Scorpius has pulled one of these on the Scarran emperor. For a time, it is unclear if his devotion to the Peacekeepers was the real fake, but when he helps destroy the Scarran's evolutionary edge, it becomes obvious that his loyalties never lay with them.
- Same season, Braca. He appeared to have switched his loyalties to Grayza following the destruction of Scorpius' Command Carrier at the end of Season 3 - gleefully aiding in torturing him for information and even shooting him. However, it was all part of another of Scorpius' plans. Braca even acted as The Mole for Scorpius while the half-breed was hiding out on Moya.
Adric from Doctor Who does this not once but three times during his tenure as a companion. Unfortunately, most fans miss the "fake" part (except in "Four to Doomsday" where he actually does side with the villain, but only because he seriously believes that Monarch's intentions are benevolent) and use it as credibility towards his status as The Scrappy.
- The Doctor himself does it in "The Almost People" when he briefly pretends to be in on the doppelgangers' murderous plan so that he can undermine it later.
Mulder of The X-Files does this in season five's "The Pine Bluff Variant". He even had to hide it from Scully, who was not pleased that she was kept out of the loop.
During the oft-maligned Leviathan story arc of the cult classic Gothic soap opera Dark Shadows, several characters who had managed to resist or overcome the power of the Leviathan cult later pretended to fall back in with said cult in order to help take it down.
In an episode of Arrested Development, Michael and Gob formulated a plan to get back at Oscar for his cruel pranks on them as children which drove the two brothers apart. Gob immediately went to Oscar and told him the plan, or so it seemed. Gob's defection was fake and part of the plan from the beginning. It was believable because Gob would have had no qualms about betraying Michael for real.

Mythology and Religion

In The Aeneid and The Odyssey Sinon surrenders to the Trojans, after claiming to have defected from the Greeks, for the express purpose of convincing the Trojans that the Trojan horse was a gift. He also added the detail that they under no circumstances should bring it into the city because then it would make the city invincible. You know the saying "never trust Greeks bearing gifts?" In context that's actually about Sinon in specific. Older Than Feudalism.
In the Biblical Book of Judith (considered Apocrypha by Protestants), our heroine convinces the Assyrian general Holofernes who is besieging her city that she will betray the Jews to him. Then she waits for him to get drunk and does this.

Tabletop Games

In the BattleTech universe done by Justin Allard whose fall from grace was manufactured to give him credibility with Capellan Confederation
In Warhammer 40,000, the Alpha Legion's true allegiance is to the Emperor, in the most twisted way possible.

Video Games

This also happens in Metal Gear Solid 3: Snake Eater. However, the Boss' fake defection is complicated by the actions of Big Bad Volgin, making it necessary for her to be killed by Snake, to cover up the entire affair (and not to mention prevent World War Three from erupting). Tragically, Snake only learns of the full story afterward.
- It gets even worse in Portable Ops, when it is revealed near the end that Not only was the launching of the nuke not only planned, but the true outlines of both the Virtuous Mission and Operation Snake Eater was to kill off The Boss from the start by a single deviously cunning strategist. Coldman even admits (with a sickening amount of glee and satisfaction, not to mention) that he was the one who set The Boss up.
- In every single Metal Gear Solid game (up through 3 at least), in fact, Revolver Ocelot is a Fake Defector to whomever the current game's Big Bad is. He always, always double-crosses his apparent boss at the end. Even more than that, he's not even typically working for the people he "defected" from, but is solely loyal to the Pro-Big Boss faction.
  - In fact he gave such behavior its name.
  - Other than the Chronic Backstabbing Disorder moments, Ocelot was stated in his backstory that he originally worked for the NSA until he and a colleague of his defected to the Soviet Union. However, it was suggested to be a fake defection due to still working for the CIA.
One story option, which will happen most of the time in Tales of Symphonia unless you choose Kratos at the Flanoir doctor scene, features Zelos doing this, in part to get one of the required elements to create the Eternal Sword. In the other story path, he really does join the villains and you have to kill him.
- If you piece all the story together, Kratos plays with this trope as well. Ultimately, Kratos doesn't believe in Mithos' vision of the world, but his inherent fatalism -- and the knowledge of what happened last time he tried -- keeps him from truly abandoning the Cruxis leader. This leads to Kratos playing the two of you up against each other and helping in his own fashion, hoping that ultimately Lloyd will win so Kratos will be able to die. He'll never actively oppose Mithos unless you choose him in the aforementioned scene, however.
Subverted in the UBW route in the Fate/stay night game by Servant Archer, defecting to one side, betraying them, then turning around and attacking his original side, revealing himself to have been acting in his own personal interests all along.
Jowy Atreides from Suikoden II is an archetypical example of this trope (and a classic Starscream. Originally the main character's best friend and ally in the oncoming war against the demonic and psychopathic Prince Luca Blight (not the Luca above mind you), he betrays said best friend and joins up with Luca, believing that the only way to stop him is from the inside. His plans are successful and in the end of the game, you can choose whether to fight him to the death of not.
- Sialeeds does this when she betrays the heroes in Suikoden V for the same reasoning as Jowy's: kill the corrupt people of the Senate from the inside so that no one will oppose the Prince and Lym.
Axel in Kingdom Hearts: Chain of Memories pretended to help Marluxia for most of the game (even killing Vexen in the process), then turns around and ruins his plans.
The "staged breakdown" version of this is the premise of Splinter Cell: Double Agent, except that the death of Sam's daughter was very real; that Myth Arc is to be continued in Conviction.

Webcomics

Darth Maul attempts to do this in Darths and Droids, pretending to betray Palpatine for Nute Gunray. Unfortunately, Gunray sees right through it.
In American Barbarian, Rick's ploy for getting to Two Tank Omen

Web Original

In The Gamers Alliance, Briss betrays the Grand Alliance and escorts one of the heroes' enemies to Trinity Gask where he hopes to meet with Big Bad Glaurung Losstarot and gain her trust. However, it's only an act on Briss's part because he's still secretly loyal to the heroes and see his defection as the only means to appear to genuinely join the villains and gain their trust so that he can proceed with his plan to gather intel. Things get a bit more complicated for him when he is reunited with his old fling Tiyana in the city and learns that she is working for the villains and is pregnant with his child.

Western Animation

In the Gargoyles episode "Revelations," as an initiation into the Illuminati, Matt Bluestone leads Goliath into a trap set by Mace Malone at the Hotel Cabal, where they intend to break him mentally and then interrogate him. Matt ultimately reveals his true intentions when he saves Goliath from being outright killed by Mace. Viewers learn in the end that Goliath was in on it from the beginning. Additionally, Matt gets into the Illuminati regardless, as the only person who didn't know his intentions was Mace, who is left trapped in the hotel for his failure and driven insane.
- In "Protection," Elisa goes undercover as a Corrupt Cop to get evidence on Draco's protection racket. Out of the loop, Goliath and Broadway notice what appears to be strange behavior and are confused by what's gotten into her. However, they pick it up fast enough and even join in the deception to help bring Draco down.
The Codename: Kids Next Door ep "Op FUGITIVE" is mistakenly thought of as one by many. Details under What Happened to the Mouse?. "Op MAURICE" is a genuine one, with the Fake Defector being a chicken-pox researcher kidnapped by Cree. As the above quote reveals, Chad (Numbah 274) was this all along in "Op T.R.E.A.T.Y.".
There was one of these in Beast Wars, with Rattrap pretending to join the Predacons. Ironically, in the first season of the sequel series Beast Machines, he actually goes over temporarily. Well, sorta... Megatron was insanely vulnerable, and he made an agreement to make sure the heroes DON'T kill Megatron. Ironically, Megatron keeps his word, outfitting the weaponless Rattrap with MASSIVE weapons. It appeared he even would have let Rattrap keep them when the battle continued, except Rattrap refused the weapons. (Turns out Rattrap's a HACKER now.)
On Exo Squad, Marsala does this once. Oddly, in a much later episode, the Neo Megas sorta pull one on him.
Raimundo pulls this off on one of the Big Bads in Xiaolin Showdown. His efforts were aided by the fact that he once actually did it for real.
The Simpsons did this one too. In the episode "A Star is Torn" has Homer acting as Lisa's agent in an American Idol-like contest. After a fight, Homer pretends to desert Lisa and team up with ~~Cameron~~ Johnny Rainbow. At the end of the episode, Homer is revealed to actually be sabotaging Johnny Rainbow's chances all along.

Homer: He's about to learn the most important lesson in the music business: don't trust people in the music business.

Tiny Toon Adventures, of all shows, pulled this off with Plucky Duck. With Acme Looniversity due to play its hated rival, Perfecto Prep, in the championship game, Plucky seems to betray his Looniversity friends and begin giving Perfecto Prep inside knowledge of the Looniversity's game plan, up to and including a copy of their playbook. On game day, Plucky gives Perfecto Prep advance knowledge of the plays the Looniversity plans to use...and the Prep students suffer a humiliating defeat. In the end, it's revealed that Plucky was made into a Fake Defector to sabotage Perfecto Prep's attempts to cheat.
In the third episode of Tale Spin's pilot series, "Plunder & Lightning", Kit Cloudkicker pretends to betray Baloo, Molly and Rebecca in the Iron Vulture to his former mentor Don Karnage, to allow them to escape. The fake deception is so convincing and surprising that Baloo believes himself betrayed, and angrily leaves Higher For Hire with the Sea Duck to Louie's to party his cares away, until he hears Kit desperately radio for help in the fourth episode.
- Watching that scene, it seems that the only reason Karnage bought it was because Baloo himself bought it... he seemed fairly skeptical, then looked at the unfeigned rage on Baloo's face and that's what sold him on it.
- That and Kit actually went so far as to snap at Molly and make her cry.
Both Cyborg and Robin do this in Teen Titans. Robin was less successful, as Slade has already figured out who "Red X" is.
An episode of Cyberchase features Digit pretending to have gone bad again and being rehired by Hacker, in order to prevent Hacker from finding the secret of invincibility.
The Adventures of the Galaxy Rangers episode "Renegade Rangers" was all about this trope, with the heroes pretending to go criminal in order to get to the Black Hole Gang. MaCross (second in charge) never believed it for a second, but Daisy O'Mega, a former Bounty Hunter who went renegade herself, is taken in by the ploy (and Shane's Chick Magnet ability).
The titular heroes in Centurions did this in two episodes, "Max Ray... Traitor" and "Cyborg Centurion". A guest star used the same ploy in "Atlantis Adventure".
Duke from The Mighty Ducks feigned returning to a life of crime after an old member of his mob came to Earth to find out what he was stealing, and why, for Dargaunus.
Done in an episode of Dudley Do Right so he could infiltrate Snidely Whiplash's fur-smuggling ring. The unspeakable evil act that got him thrown out of the Mounties? Eating peas with a knife.
The G.I. Joe two-parter "The Traitor": When Cobra learns that the Joes have developed an armor treatment that makes their vehicles impervious to their weapons, the Twins approach Dusty and offer to pay his mother's medical bills in exchange for the formula. At first, Dusty only gives them information on the Joes' strategy to stop their next attack, but as the expenses pile up, he eventually steals the formula and turns it over to them, which is followed by Duke being knocked into a coma when a "trap" he and Flint set for Dusty backfires and he's trapped on an oil rig that explodes. Dusty is convicted at court martial and given a life sentence, but Cobra attacks as he's on his way to prison and break him out. Fully indoctrinated with the bad guys, he leads two Cobra raids on chemical plants to acquire materials for their mind control gas and even helps capture an entire squadron of Joes. When Cobra Commander gives Dusty the honor of testing the mind control gas on the captured Joes, Dusty instead releases the gas into the main chamber, where it corrodes the armor-treated Cobra vehicles and Mooks, then frees the Joes and escapes. It turns out that the Joes knew the armor treatment was unstable and wanted Cobra to get it, so Duke and Dusty came up with the plan to get the formula into their hands... but nobody else knew that Dusty's defection was all an act. (Also, the chemical combination that created the mind control gas could also be turned into a compound that neutralized the armor treatment, resulting in the hilarious scenes of both tans and uniforms completely disintegrating.)
Digit from Cyberchase does this occasionally, helped by the fact that he is, in fact, a former employee of the Big Bad.

Real Life

Sicinnus: the private tutor of Themistocle's children took a message to King Xerxes at the Battle of Salamis advising him to attack. Whereupon the Persian fleet fell into an ambush.
Eric Erickson was an American-born Swedish businessman who pretended to have converted to Naziism in order to visit Germany—and scout German petroleum facilities for targeting by Allied bombers.
Ivan Susanin, who agreed to lead Polish troops deep into Russia undetected... and led them into a deep forest where nobody made it out alive.
Actually this was a pretty common phenomenon during the cold war... in order to diminish the effectiveness of REAL defectors, the USSR sent several false defectors to flood US intelligence agencies with conflicting stories. One famous example came during the Golystin-Nosenko controversy, which ultimately led to the CIA shifting completely away from human intelligence to signals intelligence (e.g. wiretapping, satellite photos, cryptography...)
One reason the Germans had such poor intelligence in WW 2 was that one of the finishing instructors in the spy school was actually an MI 6 plant, allowing them, in the first few weeks to pick up virtually every German spy.
As a congressman Heartsill Ragon worked for legislation that would become the United State's 1934 National Firearms Act (Ragon envisioned even harsher gun control). He left after an appointment by Franklin D Roosevelt (who signed the NFA) to judge, where the Case United States v. Miller would come to him. As judge of the trial Ragon declares the law he previously worked for the enactment of unconstitutional. This was no change in heart and instead a scheme to establish the NFA as constitutional. The defender Ragon forced upon Miller left after the state appealed the supreme court and as Miller was a broke criminal fleeing from his former partners the Supreme Court heard no arguments from the defense and promptly approved the law.