Amnesia Loop

A character notices something unusual, investigates it, discovers a big secret, and is given Laser-Guided Amnesia to keep the secret safe. All is well... until they notice the unusual thing again, and, since they have no memory of last time, start the same investigation over again.

Stories involving an Amnesia Loop are often told from the point of view of the investigating person, with "this isn't the first time this has happened" coming in as the big twist. Doing it that way also lets the writers establish the repetition without making the audience have to sit through it more than once.

May end with a Here We Go Again.

Contrast Groundhog Day Loop.

A situation where an investigator is pursuing a single investigation while hampered by a faulty memory, as in Memento or Ghajini, is not an example of this trope, unless it includes the specific situation where the investigator completes the investigation and then starts over because they've forgotten that they completed it.

Spoiler warning: Because of the "big twist" aspect described above, the fact that a particular work is listed as an example may be a spoiler in itself. Spoilers of that nature will not be hidden in the list below, because there is no point in an example if the whole thing is hidden.

Other spoilers, such as the nature of the secret being protected, may be hidden as usual.

Comic Books

 * Beautie in the Astro City story "Her Dark Plastic Roots" is a life-size "Beautie Doll" (an Expy for Barbie) who is unsatisfied with her life because she doesn't know her own history. She investigates and discovers she was created by a super-villain's then-eight-year-old daughter. When she confronts her creator, who is now in her forties, her creator resets her memory so that she doesn't remember her investigation, as she has done every few years as Beautie repeats her investigation. Beautie's friend and teammate MPH tells her to think about it next time, because Beautie deserves better.

Film

 * Implied to have happened several times with Leonard Shelby in Memento. Leonard is implied to have killed several people who he thought killed his wife, than destroyed the evidence of "success" after the killings, then was driven to find a killer all over again.
 * Eternal Sunshine of the Spotless Mind: People keep getting into the same bad relationships over and over, then wiping their memories of them.

Literature

 * In the science fiction novel A Deepness in The Sky by Vernor Vinge, one of the characters is in a relationship with a man who she thinks is really nice but he's really a sadistic monster. There's a scene where she finally discovers the truth about him, only to have him zap her with Laser-Guided Amnesia -- again.
 * In Vernor Vinge's short story "The Cookie Monster", the characters figure out halfway through their investigation that they're uploads in a computer simulation, and that they get reset and forget everything at the end of their work cycle. They do know that the current cycle is different, as they have an email that gives them hints on where to go, but they have to race to the goal before they're detected or the cycle ends. The characters even make the Amnesia Loop work to their advantage:
 * In Thursday Next novel, First Among Sequels,

Live-Action TV
"Spike: (laughs sarcastically) Oh, I get it. That's very crafty. Glory's worked the kind of mojo where anyone who sees her little presto-change-o instantly forgets. And yours truly, being somewhat other than human ... stands immune. Willow: (frowning) So ... ? Xander: (slowly, like a revelation) Glory can . Anya: And anyone who sees it instantly forgets. Spike: Kewpie doll for the lady. (He puts one finger on his nose and points the other hand at Anya.) Giles: Excellent. (looks around at them) Now. Do we suspect ? Spike: *Sigh*"
 * In the Doctor Who episode "The Beast Below", there's a secret at the heart of the kingdom, and Liz X is determined to uncover the truth. Part of the truth she uncovers is that she's uncovered the truth many times before, but always agreed to undergo Laser-Guided Amnesia to allow it to remain secret.
 * Buffy the Vampire Slayer season 5: whenever a human learns that Big Bad Glory is they forget very shortly afterwards; as a result the scooby gang learns this secret on multiple occasions.


 * In one episode of Star Trek: Voyager, the Doctor has to choose between two patients to operate on because he can only save one. He chooses the main character rather than the Redshirt, then has a Heroic BSOD over what he thinks was a Sadistic Choice. To cure him of this, the crew secretly erase his memories of the operation -- except the Doctor keeps stumbling upon the evidence, and going into Heroic BSOD all over again. Eventually the crew realizes that they'll just have to leave his memories alone and let him sort it out, even if it's risking a permanent crash.
 * In an episode of Star Trek: The Next Generation, this trope's played with as the crew apparently encounters an unstable wormhole and moves on, only to start finding clues of a missing time period that lead them back to that anomaly for answers. It turns out that they investigated the anomaly before and uncovered a group of xenophobic Sufficiently Advanced Aliens who'd wiped their memories to keep their existence a secret, which created the missing time period. Once the truth's revealed, the crew redoubles its efforts to cover up the events all over again so they won't go through yet another loop, since, if they come back a third time, they almost surely will get killed by the increasingly annoyed aliens.
 * Monk: In one episode, Monk realizes something he had overlooked about his wife's murder and starts to investigate. After it becomes a dead end, a witness complains that he's been coming by every few years asking the same questions. Apparently he was blocking out the fact that the lead didn't go anywhere.

Anime & Manga

 * In Tsubasa Reservoir Chronicle, every time C!Sakura figures out her missing memories are about C!Syaoran (the ones she sacrificed for them to travel dimensions), she forgets again.
 * Endless Eight. Everyone except Yuki has their memories of the Groundhog Day Loop erased at the end of said loop. This is a problem as they are trying to figure out how to end it.

Tabletop Games

 * In the old pre-reboot Mage: The Ascension, this was created by a massive spell cast around the truth of the origin of the Virtual Adepts. It was finally discovered when someone assigned to go over some stolen Technocratic information sat down to read for a few minutes, and discovered he'd been reading for several hours.

Video Games

 * The story of the Nameless One in Planescape: Torment. Every time he dies and comes back, he forgets everything about his life but then someone notices a Note to Self: tattooed on his own back, which instructs him where to start searching for his past... and said search usually ends in his death and amnesia. In the game, you control the umpteen thousandth incarnation.
 * Implied in an in-game short story. An amnesiac man meets a hag who asked him for his third wish. Since he doesn't remember the other two, she explains that he was granted three wishes, and had used the second wish to undo the effects of the first. So for his final wish, the amnesiac asks to know who he is. The hag laughs and says that that was his first wish.
 * In Runescape, this is a central plot point in the "Forgiveness of a Chaos Dwarf" quest.

Web Original

 * Ruby Quest. It's hinted early that it's not the first time You Wake Up in a Room, but the full extent is only revealed near the end: It's been going on for.
 * Phelous fell into this during his review of Triangle.

Web Comics

 * Casey and Andy: The title characters watch a movie, then decide that they want to be able to enjoy the twists again, so they erase their memories of watching it and watch it again. It later turns out that they had done this around 60 times for that particular movie.
 * In Mixed Myth, the sphynx Tamit is actually, which means she's destined to always be a mystery to herself. Any time she learns her true identity, she then forgets everything.
 * The Maze of Many in Goblins.
 * Done humorously in a Penny Arcade: A man wakes up in a field, trying to figure out how he got there ("I was running from...something...") at which point a big monster whacks him over the head. The last panel is identical to the first.

Western Animation
"Private: Oh, what's this? Amnesia spray! Fantastic! (squeezes the bottle and sprays himself) Private: Oh, what's this? Amnesia spray! Fantastic! (squeezes the bottle and sprays himself) Private: Oh, what's this? Amnesia spray! Fantastic! (squeezes the bottle and sprays himself) Private: Oh, what's this? Amnesia spray! Fantastic! (Hesitates and holds the bottle away)"
 * On American Dad, every year Francine brings up the idea of having her parents move closer to them. Every year Stan takes her to a hypnotherapist to wipe the idea from her mind.
 * On The Venture Brothers, in the fourth season, Hank and Dean keep discovering that SPHINX's secret base is in an annex of the Venture compound, and Brock keeps having to erase their memories. After a while, Brock gives up because it isn't worth the effort.
 * The Penguins of Madagascar has an episode with Private finding a bottle of "Amnesia Spray".


 * Kronk on The Emperors New School does this in order to keep Mudka's Meat Mugs recipe a secret, even from himself despite being the chef, by dropping a grand piano on himself. Hilarious in that the only ingredients in the recipe is.