Dexter/WMG

Dexter will be tried in court in the final episode of the series and WIN!
And it'll be before a jury (upon his confident request to a dumbstruck defense whose convinced he just signed his own death penalty) which, after he confesses to all his kills and delivers a powerful speech on the ineffectuality of the criminal justice system, the monstrous acts of the people he killed, the need for someone to take charge when the law won't do anything, and his own effectiveness in removing some of the most heinous killers from the streets and lowering the crime rate, the jury, with support from millions of fans who agree that heinous killers who escape the law ought to be killed and to the utter shock of the judges and attorneys, will rule him "Not Guilty" of murder and release him back to the streets amidst thunderous applause with full support for future killings. Cue a media frenzy of the first nationally sanctioned serial killer whom people everywhere admire. Plus Deb, Angel, LaGuerta, Masuka and friends will all be there, finally accepting him for who he really is and Dexter will have come to terms with himself and realized that he's a hero after all.
 * Putting aside for a moment the fact that this is all fantasy (we know that from season 2, Dexter would NEVER deliver a speech in defense of his own actions. Also, any prosecutor worth his salt would simply point out that Dexter could have called in anonymous tips, and saved just as many lives.
 * Not nearly as awesome though. And as for the last part--yes, because we all know how fast acting the police are to confirmed, verified problems, much less dubious "anonymous" tips indicting supposed upstanding pillars of the community who can easily hide their crimes from the police like they did to begin with--hence the need for Dexter to investigate them "outside the boundaries of the law".
 * To add to this WMG, the ending scene of Season 1 is actually the last scene of the *series*, taking place at the end of the final season.

Dexter commits suicide in the final episode of the series
As the show goes on and on, we see that Dexter definetely is not emotionless, and cares a great deal about those around him (it's possible that even Dexter himself is realizing this). Perhaps near the end of the series Dexter will develop a conscience about killing, or will come so close to his loved ones finding out about his secret life that he will orchestrate his suicide in such a way as to take down the final series' Big Bad in a way that both kills the Big Bad and makes Dexter's suicide look like a murder. He will do this to protect the minds and lives of his children and Deb.
 * Dexter is not completely without a conscience; but since the Code gives him a justification for what he does, he doesn't see it as a violation of his personal morality. But even if he never develops empathy for the people he's been trained to see as victims, he has appeared to struggle more with his Dark Passenger than he used to. Suicide may ultimately be the only way to escape it, as Dexter reflected when he saved Trinity from killing himself.
 * Except that the topic of Dexter committing suicide has already come up before in the show, by Doakes for example, and Dexter readily dismissed it as "pathetic".

Trinity is Barney's father from How I Met Your Mother
Obvious facts (AKA John Lithgow-ness) aside, Barney's father Jerry has hints of a more exciting past life, and his picture-perfect family does seem eerily reminiscent of the initial portrayal of Trinity's family, right down to the estranged much older child from a past relationship. Alternatively, they're an alternate universe version of the same family.

The Dexter series finale will be a Mind Screw a la The Prisoner
The first two seasons had a healthy dose of surrealism, and so they may go this route for the Grand Finale.

Dexter will be mortally wounded while attempting to subdue a victim. He manages to kill him in the fight, but he is slowly bleeding to death. Dexter manages to drags himself to his kill room, but the blood loss will make him hallucinate that all of his friends, enemies, and loved ones are coming to judge him for his crimes.

The last one will be Rita.

Think about it. It would be the perfect way to bring back not only Rita, but also Doakes, Brian, Trinity, Miguel, and maybe Lila.
 * Yeah, and when he accepts his fate, they all start clapping and say "Congratulations!"

Quinn dies at the end of season 5 due to Deb's Curse
Seriously, how does she still pull men when the last 3 of the 4 she dated were killed or skinned? The only two that (we think) survived were only in like 3 episodes. Quinn dies, and this troper bets Dexter does it.
 * Alternatively, she will leave him for Lundy. You know, his corpse. Okay, I just squicked myself.
 * As for Season 5, Jossed. It may still happen later though.

Chickey Hines taught Brian to kill, and also slipped the idea of a 'code' to Harry in the first place.
The seemingly 'innocent' Chickey Hines has been behind nearly everything all along, for decades. It was he who tipped off the drug dealers to Laura Moser. Harry adopted Dexter before he could, but he got to Brian in his early adult life and taught him how to kill and get away with it, but it was too late to instill in him the idea of a code. However, years before he did manage to slip the idea of a code into Harry's mind one night late at a bar. His goal was always to damage two children and train them to be the perfect killers, the keep the streets clean of the monsters that he didn't he the guts to take out himself.

Unfortunately for him, this all went afoul when Miguel Prado saw him for the monster he was and took the opportunity to put him behind bars, even if he didn't commit that particular crime. However, he'll be back. Dexter will have to meet him someday, and there will be blood.

Dexter is Dexter from Dexters Laboratory.
See the WMG page for details.
 * Here you go.

Captain Matthews is....something
No idea what, exactly. Season 4 painted him in a darker light than before, but there's always been something kinda off about him. He's always known more than he shares. He knew Harry killed himself (well, that's what's been established so far at any rate). He apparently knew who Laura Moser was and knew about the ice truck killer connection to Deb and Dexter at least as early as the end of season 1. And he's gone from being antagonistic towards La Guerta for legitimate reasons (her political maneuverings) to just being sinister and petty (seriously? Trying to screw her over for having a relationship? Because she's 'arrogant'? Wow. It doesn't help that La Guerta has been developed to the extent that she's lost a lot of the bitch she had from season 1, but even if this had come up in season 1 this feels like real overkill). So....just how far does the captain matthews rabbit hole go? Consider that question and it'll lead you to some interesting places. If he knows about Brian Moser...does he know about Dexter? Is it more than just plot convience that lets Dexter escape an FBI manhunt and kill a DA one year later without being caught? Was there an ulterior motive for the captain's insistence that Neil Perry was guilty of the ice truck murders despite La Guerta's protests (was he really taken off guard when it blew up in his face? He recovered rather spectacularly well from that blunder. Almost like he was prepared to roll with it....). Was Harry really helpless to deal with Dexter's urges any other way aside from his code, or did someone else have a hand in shaping the serial killer's serial killer? For that matter, when Harry was having second thoughts about what Dexter had become, did he really turn to suicide, or did someone decide to 'help' him along that road when he voiced his protests and desire to get Dexter real help? And then too....isn't it interesting that the drug dealers knew to look in the park that day to find Harry and Laura, or that they knew enough to say Laura was informing and sleeping with Harry? Did someone give out information to the drug runners that led to Laura Moser getting the chain saw and Dexter getting a dark passenger? Just saying, Season 5 could bring up some interesting explorations of a man who has gotten progressively more suspicious as the seasons pass.
 * Captain Matthews is the G-Man

Rita is going to find Dexter's blood-slides.
It will be the cliffhanger to end all cliffhangers. Then Dexter will tell her that the slides are mementos from especially hard cases of his. Rita will choose to believe him since, well, she is kind of stupid that way.
 * ...or
 * Ever consider that
 * Since when
 * It's been a mildly popular theory. Dunno why.

Dexter is an AU counterpart of Light Yagami.
They're both serial killers who kill killers.
 * Addendum: Their standards are very different. Light kills to create what he would consider the perfect world, and he thinks of himself as the incarnation of justice. Dexter's only reason is his urge, and he is far from being proud of it. Dexter EXPLICITLY limits his targets to those who have committed murder. Light's target are not only murderers, but also petty criminals and eventually everyone he considers a "burden to society". Light is pride and presumption incarnate; Dexter probably isn't.
 * Also, Dexter generally rules out killing people who served their sentences. Light kills dozens of people already behind bars.
 * Dexter most certainly isn't, when anyone tries to give him some kind of Not So Different speech or anything of the sort he simply agrees. He even tells Miguel "You're all just unchecked versions of myself. The only difference is I know I'm a monster." (Paraphrased)
 * While Light and Dexter share many similarities (both are Serial Killer Killers that come from police families, have a Morality Pet sister, a traumatized Beard girlfriend/wife, and are very good at hiding their gruesome hobbies Dexter is almost an anti-Light:
 * Light thinks he's a God, Dexter thinks he's a monster.
 * Light becomes a monster because he was such a Wide Eyed Idealist to begin with. Dexter is more cynical and finds youthful idealism dangerous.
 * Dexter believes the world would probably be better off without him (not that he's in any hurry to make the world "better off"). Light thinks he's doing the world a favor and feels entitled to rule it.
 * Dexter is a killer in the traditional sense-he gets intimate with his targets and carves them up. Light is a Non-Action Guy (and considering all that happens in the series, it wouldn't be surprising if he even had a phobia of guns and violence like Dex has an ironic phobia of blood.) Light commits mass murderer using magical means—he kills from the comfort of his room by writing names in a notebook. There is no sense of immediacy, no blood, no struggle. His targets are dehumanized and the act of taking so many lives would likely have all the psychological impact of a kid playing video games—look, I killed over 10,000 evil Mooks—aren't I grand?
 * Dexter sees killing as playtime, Light claims it's a great burden / sacrifice on his part (though, like Dexter he seems to get an almost sexual enjoyment out of killing.)
 * Light likes to plan out his next move 20 steps ahead and while Dexter carefully plans out his kills he tends to do things more on the fly.
 * Dexter is very witty in his Inner Monologues, Light doesn't have much of a sense of humor.

Alternatively Light Yagami is another of Dexter's long lost (half-)brothers.
As noted on the Death Note WMG page Light Yagami looks nothing like the rest of his family with his (red-)brown hair but he does kind of look like Dexter. Dexter,  and Light could share the same vicious bastard of a biological father. The mother was a Japanese woman and, after Light was concieved, she returned to Japan and either dies after giving birh or abandons the child and, like Dexter, Light is adopted by a police officer but that's where the similarities end. Light is very much "an unchecked version" because unlike Dexter who had Harry and the Code, Light was raised so sheltered and made to adhere to such strict morals that he can't cope with the very idea of evil in the world or himself in any terms other than Kill It With Fire!!!!!111 (or rather heart attacks). However since Light didn't have the same trigger as Dexter  it took some extra encouragement to trigger his Dark Passanger. Notably when Light  he lacks the same evil and cunning that he has when he uses it. Something similar happens to Dexter when he, for a time  in the Dexter book series.
 * That would be an interesting family reunion: they'd be all affable in their charming personas (and they could trade fashion tips on those awesome shirts: Hawaiian vs. the male model catalogue) and then try to kill each other when they figure out their true colors. Light would probably run rings around Dexter as the Chessmaster but on the whole he is a Non-Action Big Bad and Dexter would more than likely win in any physical confrontation.

Dexter is an alien.
One preview has someone say something along the lines of "Dexter is an alien! Oh wait, I just gave it away". This is not a joke. It's a hint of what's going to be shown at the end of season four.
 * Jossed for Season 4, but the general theory could still be true.
 * This is rather unlikely. In the books, the Dark Passenger is a seperate (apparently supernatural) entity. In the series, this wasn't used because they didn't want the series to run as Mystery or Science Fiction. So I doubt they'll take up something like this.

Someone will write Dexter/Miguel slash fan fiction.
All thanks to this:

"Miguel: I am the last person you wanna fuck with because I WILL FUCK YOU BACK IN WAYS YOU NEVER EVEN IMAGINED."


 * Yeah, it's been done. R-rated, natch.

The Ice Truck wannabe Neil Perry is the same Neil Perry from Dead Poet's Society.
He faked his own death and moved to Florida.

Dexter is Number 16

 * Think about it; Dexter is a deadly killer, loves blood, and was taught his skills from his adoptive father. Number 16 was part of the assassin lineage, painted his secret messages to Desmond in blood, and most assassins, like Ezio, were taught by their fathers or a father figure.
 * One problem: if Harry was an Assassin, why would he choose to be out in the open? Most Assassins were in communes (Desmond prior to leaving) or working undercover in Abstergo (Lucy). Unless... Miami Metro is secretly a Templar front.

Harrison will grow up to be a Serial Killer.

 * This was already hinted at in the end of season 4, before he was even born.

Alternatively, Harrison will NOT grow up to be a Serial Killer.

 * If Dexter knew how to control or stop the urges, he would do it for himself too.
 * He couldn't do it for himself because it's been a part of him for over 30 years. Grooming Harrison from that early an age makes it more likely that he could fix him.
 * He couldn't do it for himself because it's been a part of him for over 30 years. Grooming Harrison from that early an age makes it more likely that he could fix him.

Deb finds out about everything.

 * Deb finds out about this in the first book, but the show is doing things differently. Doesn't mean it's not inevitable.
 * Although her reaction might be different to the books. This troper thinks that if TV Deb found out her brother's a serial killer, that'd be the straw that breaks the camel's back and would well and truly fuck her up for the rest of her life. Seriously, I wouldn't even rule out suicide. She's relied on him whenever she's gone through some major shit, and this'd be like breaking a house's major support beam or whatever.

Both Arthur Mitchell and Rita will reappear in season 5.
In Dexter's mind, of course. (Mainly because both are awesome characters.)
 * If I remember correctly, Julie Benz was confirmed to be leaving. A wasted opportunity, since they could always have her as a ghost a la Harry, reminding Dexter of his good natured self while Head Harry could keep Dexter on the code. Head Arthur could be a manifestation of the Dark Passenger wishing to be released. Is this too Id, Ego and Superego for the show?

It wasn't Trinity who
The timing doesn't make any sense, she doesn't fit the pattern and we don't even know completely if Trinity knew where to find her. Suicide is actually more believable.
 * I don't think it was Trinity-- Trinity didn't even know
 * It was pretty firmly established that Dexter pissed Trinity off something fierce, it's possible that he had time to do some research and find out where Dexter lives and did it because Dexter had "turned" his family against him. It fits.
 * It was pretty firmly established that Dexter pissed Trinity off something fierce, it's possible that he had time to do some research and find out where Dexter lives and did it because Dexter had "turned" his family against him. It fits.
 * It was pretty firmly established that Dexter pissed Trinity off something fierce, it's possible that he had time to do some research and find out where Dexter lives and did it because Dexter had "turned" his family against him. It fits.
 * It was pretty firmly established that Dexter pissed Trinity off something fierce, it's possible that he had time to do some research and find out where Dexter lives and did it because Dexter had "turned" his family against him. It fits.
 * It was pretty firmly established that Dexter pissed Trinity off something fierce, it's possible that he had time to do some research and find out where Dexter lives and did it because Dexter had "turned" his family against him. It fits.
 * It was pretty firmly established that Dexter pissed Trinity off something fierce, it's possible that he had time to do some research and find out where Dexter lives and did it because Dexter had "turned" his family against him. It fits.

The ghost of Harry is actually how Dexter imagines the Dark Passenger
Pretty much spent all of season 4 is spent telling him to stay away from his family and kill properly. Even considering what we know about Harry, this doesn't sound like what he would advocate.
 * Either that or its even more convoluted, upon seeing the blood in the container, Harry used the Morloch connection to transfer his darkness to the kids. This then continued after his death in a kind of sadistic possession. Either way, the ghost of Harry possessing Dexter at the moment is evil, whether or not he is actually Harry.

Masuka
He seemed to take  worse than anyone else in the department and was absolutely crushed when
 * In the books, Dexter is friends with Masuka because  This hasn't been mentioned in the show, but still...
 * In the last episode of season 4, it is heavily implied that Trinity at least knew of Rita's death. How could he have known if he didn't do it himself?
 * This theory doesn't hold water at all; Masuka was distraught rather than angry over the secret he was keeping, and showed visible relief when Dexter told him he already knew. If his motive was to 'protect' Dexter, how could he possibly achieve this by

Dexter isn't really a sociopath
Got the idea from Dexter's IJBM page where people discussed the sketchy approach to the whole illness as written by writers who aren't sociopaths. Dexter has the urges to kill, but isn't an actual sociopath or else Harry wouldn't have to emphasize emotional detachment in his code. Harry didn't want any emotions to get in the way so he convinced his son of his sociopathy and left Dexter to grow up with a massive sense of denial. He actively denies having emotions throughout the series, much despite the contrary and only starts to give in as Harry's Code slips up more and more, culminating towards the end of Season 4.
 * Which in turn suggests that Harry, in keeping with his character, put his passion for duty and need for justice far ahead of his adopted son, and turned him into a vigilante just to deal out justice to those who escaped the police. Dexter's "sociopathy" is a complete fabrication by Harry to give himself an excuse. Further, Harry killed himself because he could never forgive himself for what he did to his son to suit his own ends.
 * As the show continues, we get more and more evidence that Dexter, while severely messed up, is not a sociopath, and that Harry treating him as one (that is, as incurable) served to mess him up even further. Whether Dexter will realize that he isn't a sociopath is another matter.
 * While there is obvious evidence that Dexter is not a typical sociopath, what Harry did probably had some good and bad effects on Dexter's mental state. Harry reinforced the idea that Dexter needed to kill and that he was a monster, that there was nothing he could do about it, that he could only fake relationships and emotions (and so never taught him how to deal with real ones), but on the other hand he also loved Dexter unconditionally, understood him, and provided him with the means to control his urges. Harry didn't just give Dexter the Code, he was Dexter's first human connection, and Dexter has been looking for that connection ever since. Even if Dex isn't a sociopath, without his father's love and guidance he might have slipped further from humanity and become something even worse than the self-aware, conflicted Serial Killer Killer we all know today.

Doakes really was the Bay Harbor Butcher.
Ok, stay with me. Dexter is delusional, and the show is from his perspective, and at least the first two seasons are his recollections of past events. He's compelled to figure out who committed murders, but doesn't actually kill the murderers, he only imagines that he does (hence why he never gets caught, and coincidences always work out in his favor). Doakes really did go nuts and kill some escaped serial killers, but in much smaller numbers than Dexter imagines himself killing, and after Doakes got caught and killed himself in the explosion, Dexter's deluded mind inserted himself into the place of a real-world equivalent of what he imagined himself to be. He actually did kill Freebo and Oscar, but it was in self-defense, as he told Miguel, and then Miguel really did kill Ellen Wolf (this may have forced Dexter to kill Miguel, or some other circumstances may have happened). In Season 4, he really did figure out who Trinity was, and started following him around, as part of his delusion.
 * Alternatively, the number of kills Dexter actually commits are wildly exagerrated by his psychosis, hence why he seems to think he commits about a murder every week or so, and is nearly crazy after a month at the beginning of season 2, but after a decade at it at the beginning of the wasn't even able to fill up a single box of blood slides.
 * It's not exaggerated. In the "Early Cuts" animated episodes (which are canon) it's clearly stated that Dexter didn't start collecting slides until late in his life. Up to that point he didn't bother with trophies at all.

That cop(I forget her name) killed the headless woman
She was having an affair with the woman's husband, then killed her in a fit of jealousy. She dressed up the head in the style of the Santa Muerte cult, then made sure she was first on the scene in order to mislead the police. When the husband commited suicide she was the first responder again in order to push the investigation away from herself.
 * Unlikely considering the events of the raid in "Beauty and the Beast", and also considering there have been two deaths with a machete.
 * Jossed. She could (and probably is, this is Dexter were talking about) still know more than she's letting on.

The "Take It Now" self-help deal is part of the ring Boyd Fowler ran in.
Considering it was a focus of Boyd's character for two episodes, it's entirely possible. It has a pretty strong message that obviously spurred Boyd on.
 * As of "Circle Us", confirmed.

Dexter is seeing The First Evil.
Dexter suffers from trauma, repressed memories and a cold detachment from emotion. This never results in hallucinations until season 3 when he starts seeing the "ghost" of his dead father. But that's only because The First is manifesting as Harry. The First's motivation is that it needs time, possibly millennia, to build up its army again. Hence it is biding its time and in the process decides to mess with severely psychically damaged people. You know, for shits n' giggles.

Lumen will be a villain and will be killed before the end of season 5.
Because she knows too much for the show to go with her. Everyone who learns who/what Dexter is doesn't last long, and it's because they always turn out to be antagonists. No, Dexter & Lumen cannot become partners in crime, as that was so thoroughly deconstructed with Miguel.

There are always two villains in the Showtime storylines, one a close personal villain for Dexter and the other a general villain for the police. (Lila & Doakes/BHB, Miguel & The Skinner). In season 4 they were both the same person, but still fall this way to reflect Arthur Mitchell's double life, one as the notorious Trinity Killer and the other as Dexter's new role model Arthur. And like Lila and Miguel before him, Arthur's personal life is only subverted in the final few episodes.

We have the serial killers for this season in the beheader(s), it is too late in the story to introduce a new major character, and so the personal villain will be Lumen.


 * Maybe. Still a really likely theory, but this season seems to be messing with expectations, the beheaders now out of the picture. It's also hinting that Lumen may be a reconstruction, Dexter even saying that she may be able to know his secret unlike Miguel and Harry before her. She's also becoming a bit of a Love Interest...
 * She doesn't seem to be turning out a villain, but the pattern doesn't look good--every time Dexter hopes that he's found a friend who can accept his dark side, he ends up having to kill them (Ice Truck Killer, Lila, Miguel, Trinity). One way or another, I don't see Lumen surviving the end of the season.
 * Jossed. She survives and appears to lose her Dark Passenger, freeing her of her need to kill.

Dexter will die in the series Grand Finale
Lumen will stay with Dexter and somewhat become his apprentice, something he couldn't achieve with Miguel. They for what ever reason have a falling out, and Lumen realizes that Dexter himself needs to die. The last scene of the series will be him on his table looking at old clippings of the Bay Habor Butcher, being stabbed in the heart. That or it will be a Distant Finale with Harrison, due to Generation Xerox, ending Dexter's life everything coming full circle.
 * If he is killed by Lumen, there will be a spinoff series called "Lumen" or "Illumination". If he is killed by Harrison, there will also be a spinoff, but in a Science-Fiction setting Twenty Minutes Into the Future.
 * I've always thought so myself. Dexter is a great character for the series, but the fact that he is a vigilante serial killer, plus having killed at least two innocents in the show (one of them willingly) makes for him to have done hoops around the moral event horizon several times. I think he will finally loose his dark passenger, but either: be discovered and sentenced to death or life in prison, or die in a redeeming fashion.

Debra will get to know about Dexter's "hobby".
There are several plot elements that seem to build up to this, like Debra shooting a man without feeling remorse and talking to Dexter about it, or that guy who investigates Dexter for Quinn. (In the books, Debra knows from book 2 on.)

Dexter will take on an apprentice...
Sometime after the events of the series, Dexter will have holed up in some part of the country, doing his work despite it's having destroyed his life. In that time, he will encounter a young man with a darker past than his, who is struggling with homicidal intentions and needs to be taught when is the right time to let these urges come to the surface. He'll be living under an alias at that time, the legacy of his family's long history of law-dodging, but rudimentary investigatory work will reveal his birth name as Shane Botwin

Inland Empire (or parts of it) is Lumen's background story, or the story of another of Jordan Chase's victims, told by an Unreliable Narrator.
No real reason, but Nikki Grace would also fit the profile of Jordan Chase's victims. It doesn't really make sense, but then, considering Inland Empire, what does? (This Troper actually got the idea to this theory when, in one scene of the last Dexter episode "In the Beginning", Lumen was shown watching the DVD recordings of her own torture, a scene somewhat similar to some Inland Empire scenes.)

The police are going to capture Lumen in the season finale and she is going to go down alone for the murders without ever revealing that Dexter had helped her.
Because I think it would be a pretty good twist.
 * I always thought this too. It would have been a thousand times more interesting then her just leaving.

Debra will kill Jordan.

 * She didn't, but that would have been cool.

The guys of Jordan Chase's Circle are actually the kids from South Park grown up.

 * Jordan Chase / Eugene Greer is Eric Cartman. Both are fat as children, although Chase loses weight after the rape of Emily Birsch. Also, both are ruthless sociopaths and like to give speeches.
 * Boyd Fowler is Kenny Mccormick. Mainly because he is the first of them who dies, but also because he has the lowest social status of all five. Also, both Fowler and Kenny are arguably the kinkiest/most sexually perverted member of their respective groups.
 * Cole Harmon is Kyle Broflovsky. First, there's the phonetic similarity of their first names. Also, it's implied that Cole Harmon is the guy who constantly cleans up Chase's messups, and both can't really stand each other, much like Kyle and Cartman.
 * Alex Tilden is Leopold Butters Stotch. Remember how he whined that all was Chase's fault just before he was killed by Lumen?
 * Dan Mendell is Stan March. Again, phonetic similarity of their first names.

Dexter would have grown up to be a violent criminal anyway.
Even if Dexter's mother hadn't died in the shipping container, she probably wasn't the best mother, being a crackhead who took her two little boys to a dangerous drug deal even though she feared for her life at the time, and his father was a criminal who'd done jail time, if I remember correctly. Harry probably did a better job raising Dexter than his biological parents would have. It's not unlikely that Dexter would have grown up to be some kind of criminal, given his circumstances, even if he'd never been traumatized by his mother's murder.

Lumen never existed.
She was actually a delusion that Dexter created in order to cope with Rita's murder. On the heels of his failure to protect his wife, along comes this blond victim who not only serves as someone Dexter can rescue like he couldn't do with Rita, she also fulfills Dexter's fantasy of being appreciated for his "work" and being treated like a hero. Not only that, but when he is fully revealed to her, she accepts him implicitly, offers him understanding and love, and is the "light" to his dark. He also helps her to get rid of her darkness like he is unable to do with himself. Ultimately, however, she leaves, because Dexter can't truly bring himself to believe that anyone can accept him for who he is, and he realizes that their relationship was nothing more than an imagined wish.
 * Nope. Other people interacted and see her, Deb, Quinn, Jordan Chase, Elliot (the neighbor), the Head of Security guy, etc.

In the series finale...
"Harry: Dexter, did you kill the dog?
 * Dexter will be caught, but will work something out with the police where he helps catch murderers.
 * Or, he'll be caught, but the last scene will be Debra visiting him in prison and saying that she needs his help to catch a new serial killer that is on the loose.
 * Or, we think he is caught, until the last scene is a shot of a car driving at night, we see his eyes reflected in the rear view mirror and we hear his voice over say "Tonight's the night."
 * He does off the deep end and/or kills another innocent (or gets nabbed for killing that photographer). He will be caught. By Deborah. And he allows/forces her to kill him to end it.
 * Dexter will have been caught committing a murder, end up being tried, sentenced, and taken to the electric chair. The executioner will flip the switch, and then...it will be revealed that the entire show is just a nightmare Harry had in the split second after asking Dexter (8 years old) if he killed the neighbor's dog (when Harry first realized that Dex was a serial killer). Only this time...

Dexter: What?! No! I'm not a psychopath!

Harry: Thank god...for a moment I was worried."


 * He dies and the torch is picked up by Astor with Dexter as her Harry/Dark Passenger figure.
 * If he doesn't die, and little Harrison is killed off by the end of season six, we could expect a "The Nativity" style torture then murder. That and Dexter will be at an obvious breaking point where an important decision is made. It's either continuing to follow his dark passenger or put those he cares about the most first indefinitely.

The nanny will end up raising Harrison.
Dexter will either a) realize that he cannot give his son the life that he wants for him, and will ask the nanny to Give Him a Normal Life, or b) get caught or killed by the end of the series, in which case the likely candidate for who gets Harrison would be Deb, who, let's face it, isn't really parent material and decides the nanny would do a better job than her at raising the child.

Special Agent Frank Lundy was once Special Agent Dale Cooper
He escaped the Black Lodge and continued his work for the FBI. Notice Special Agent Lundy is chipper, upbeat, has precise unique methods and is obsessive about food. He even ends his time on Dexter by saying he is going to work on a case in Portland, OR. Back to where he started...
 * Although it would be cool, I don't really think so. Unlike Cooper, Lundy shows no signs of any present or past interest in Tibetan Buddhism or New Age Mysticism.
 * He does present a rather Buddhist mentality towards life, just not naming it as such. Stopping for Lunch precisely at 1pm to enjoy the sunny day. Keeping his mind open and clear to observe that which all others are missing. He might not be as quirky as he was in his youth but maybe he has mellowed out some . ..

Debra already knows about Dexter
She's repeatedly shown to be an extremely skilled detective. She would have figured it out by now, what with Dexter showing up at Trinity's house without a police vest only to And she knows that he was related to Brian Moser. Then there's Quinn's theories about Dexter in the fifth series, which must tip her off slightly. We see how suspicious she is when she meets Lumen, and it's right around this time she decides that there are a couple committing the murders. She lets Dexter and Lumen go and never asks to see their faces so she can continue to feign ignorance around Dexter, because she doesn't want to become an accomplice.
 * There was a moment in the fifth season finale where it appeared that Debra might have recognized Dexter from behind the curtain. She kind of pauses and makes this odd face when she looks at the blurred figure of her brother, as if maybe she suspected that it was him even though she couldn't see him clearly. Maybe she didn't want to see their faces for fear of having her suspicion confirmed.

Lumen will return at some point
Her departure seemed unnatural. And I could be wrong, but I'm pretty sure that her Dark Passenger leaving like that is not how it works.
 * She'll come back nine months later to dump a baby on his doorstep, then vanish. In all seriousness, though, I doubt she will be back. And as for her Dark Passenger leaving, she never really had one. At least, it wasn't the same as Dexter's, which got into him when he was very small and only just developing mentally. Lumen was already an adult and thus would have an easier time being able to overcome her traumatic experience.

There will be an episode focusing on the kill-shirt.
Because Dexter's kill-shirts are awesome. The episode will start with the kill-shirt being destroyed, accidentally set on fire by Masuka when Dexter was trying to hide it. Then, flashbacks will show the development of the kill-shirt throughout the years (times it saved his life, Dexter's victims complementing him on it before they died...), eventually leading to its origin: it was a birthday present from Deb. At the end, Dexter will say a tearful goodbye to his kill-shirt...then go to his room and reveal that he has a closet full of them.
 * I'm fairly certain that Dexter uses a different kill-shirt for every kill and tosses it along with a set of knives and all the plastic wrap he gets for each kill. That being said I think this a detail overlooked by the writers for the sake of simplicity because in reality when Miami Homicide found the Bay Harbor Butcher remains if they also found a bunch of the same type of shirt and knife sets it probably wouldn't be too hard to track down who had bought said items en masse.

Colin Hank's character and his sister will be duo killers
and it will be used in comparison to Deb finding out Dexter's secret. There will ptobably be a moment of one of them wondering if they'll become that way.
 * Or Colin Hanks will be the killer keeping his secret from his sister, and the same comparison will be made.

The entire show is told in flashback
The finale episode reveals either that Dexter is recounting his entire life and career to a reporter as he sits on death row, or he has made it to a ripe old age, and has written a memoir about his 'real' life, kinda like an OJ Simpson "If I did It" sort of thing. The latter, of course is a somewhat happier ending and thus, is obviously not going to happen. The only flaw I see in this is the rather convoluted form the show takes on. Having flashbacks within Flasbacks is strange.
 * How I Met Your Mother has flashbacks within flashbacks WITHIN flashbacks sometimes. A few times even adding an extra layer of flashback.

Gellar (the character played by Edward James Olmos) isn't a real person.
He's Travis' Dark Passenger. Until now, we haven't seen him do anything himself. He just gives instructions to Travis, who does all the real work.
 * Alternatively, he's a darker version of Harry, someone who used to be alive and real, and now sticks around and forces Travis to do things, instad of Harry who wants Dexter to have a good life.
 * In the last episode, we saw Gellar's old website with an image of his face on it. So this is probably Jossed.
 * That doesn't joss anything. He disappeared years ago, who is to say that it was really him who updated the site? And look at the scene in the cafe, where the waitress ignores him. Or how he got into thebedroom all of sudden? My bet is that he teached Travis how to be a religous nutcase, died suddenly and now Travis is imagining him. He "sleepwalked" the abduction of the waitress.
 * Good point. After all, Harry was a real person too.
 * As of episodes 6 & 7, he's definately been doing... er, stuff. So this is Jossed unless Travis is doing things he can't remember while in the "Gellar" persona.
 * But we have never seen him do stuff while Travis is somewhere else, doing something else. Also note how in the very same episode, Brian physically throws a bodybag at Dexter, pitchforks the motel-owner and grabs Dexter by the head. I thought that the rules of the dark passenger where shown specifically to justify Gellar doing stuff when it's revealed later that he is not real.
 * As of episode 8, . So, unless Dexter has an ability to , this is probably finally Jossed for good.
 * Actually
 * Therefore, since the show appears to be trying so hard to undermine the reality of Gellar, there will be an Untwist when he turns out to be real.
 * As of episode 9, this is no longer a theory.

Gellar will
Gellar will probably not be very happy with what Travis did. We have seen how he punishes Travis for even small deviations.
 * This is (sort of) a question of semantics.  So, in a way, he did.
 * This is (sort of) a question of semantics.  So, in a way, he did.
 * This is (sort of) a question of semantics.  So, in a way, he did.

Gellar plans, and has planned all along, to make Travis his last victim.

 * Unless, this is Jossed as of episode 9.

Lewis (Masuka's intern guy) will turn out to be Brian's son.
The ages fit, they look rather similar, and it would explain  Also, it would be another reason for them to , as opposed to just Rule of Cool. If they're going to have one of his relatives pop up, they'd need to remind the audience of who he is.
 * They do look a bit similar, and I have wondered if he is another brother -- but the ages fit? How young do you think Louis is? I say he's within 10 years of how old Brian would be.
 * If Brian was a teenage when Lewis was born it would be possible for Brian to be the father. Especially because if Dexter was able to attend medical school, as Doakes sates he did/could have when confronting Dexter with the results of a background search, Dexter would at a minimum have to be in is mid thirties placing Brian around 40ish.

The "endgame" for seasons 7 & 8:
Louis is obviously the big bad for season 7. Judging by the evidence, he will either be some kind of copycat killer or an anti-Dexter vigilante. Deb will have yet another drawn-out internal struggle about her independence and her brother, resulting in the decision that he's gotta go. The final season will be similar to Season 2, where Dexter is the main villain, and it will play out as a chess game between Dexter and Deb, which Dexter will ultimately forfeit.
 * I think Louis will be more like Brian in the first season only less experienced.

The first words Dexter will say in season 7...
"Debra, get out of my church!"

The next season will be a Dexter / CSI: Miami crossover.
Horatio Caine: "Seems like the blood of Christ..." *puts sunglasses on* "...is not the only blood in this church." - YEEEEAAAAH!

Ghost Harry will be Dexter's final victim.
In a show this rife with embarrassingly obvious symbolism, metaphorically putting Harry on Dexter's table seems inevitable. If they're going to make the last kill a big one, that'd be the way to do it.
 * Alternative: Harry somehow faked his suicide and is still around, and by killing him, Dexter also metaphorically deals with his own "inner" Harry.