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 exact same investigation all 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 where the character is fully aware of the repetition. See Amnesiac Resonance when information from a previous loop seeps into the current one.
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.
- 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.
- 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.
- Beautie in the Astro City story "Her Dark Plastic Roots" is a life-size "Beautie Doll" (inspired by 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.
- Point Blank: This is what becomes of Grifter's attempt to investigate Lynch's shooting, due in no small part to his drinking problem.
- In Eternal Sunshine of the Spotless Mind, where technology exists to erase unhappy memories, people keep getting into the same bad relationships over and over, then having their memories of them removed.
- 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. If Eddie is to be believed, they killed the person who broke into Leonard's house a long time ago and on top of that, its actually Leonard himself who accidentally killed her, though she's as much to blame.
- 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, only to be detained by his guards and dragged off to have her memories selectively erased, with the guards' dialogue making it clear this isn't the first time this has happened.
- 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. When they reach the end of the line, they find out that they've repeated the cycle of following the email to the programmers' lair over 1000 times already. The characters even make the Amnesia Loop work to their advantage: by tipping off the programmers at the beginning of their cycle, they have a whole subjective year to get closer to escaping, sabotage the controlling scientist's attempts to keep them from noticing discrepancies, and pass on everything they've learned to the next cycle.
- In Evan Hunter's novel Buddwing, a man awakens with amnesia and starts to piece things together. In the end he remembers that because he was a perpetual dick his wife committed suicide, and the shock and guilt gives him amnesia again. The book ends at the same place and situation at which it started.
- The children who are Amnesiac Gods in John C. Wright's Chronicles of Chaos get this repeatedly, until they escape the school.
- Thursday Next series:
- In First Among Sequels, Thursday finds out that her daughter, Jenny, isn't real. Landen tells her that he has to reveal this to her a lot, especially on bad days. The scene ends with Thursday asking where Jenny is and Landen makes an excuse that Thursday accepts and she moves on.
- In The Woman Who Died a Lot, Jenny keeps moving around the family. And other things occur that, in hindsight, show that memories were tampered with. Finally, an intervening force straightens it all out, and at their request, lets them believe that Jenny was a real girl who died.
- Arrested Development: GOB spends most of 2007-2012 in a "Roofie Circle".
- Black Mirror's "White Bear" is all about the punishment of a woman who watched (and recorded) her boyfriend burning a kidnapped child to death. Her punishment is to have her mind wiped and then chased around for a day by armed maniacs while hundreds of people stop to record her on their phones. Then when the day is complete they wipe her memory and do the same thing again, and again, and again.
- Buffy the Vampire Slayer season 5: whenever a human learns that Big Bad Glory is hidden/trapped inside the body of Ben they forget very shortly afterwards; as a result the scooby gang learns this secret on multiple occasions.
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 ... Ben and Glory ... are-are the same person?
Xander: (slowly, like a revelation) Glory can turn into Ben, and Ben turns back into Glory.
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 there may be some kind of connection between Ben and Glory?
- Doctor Who:
- In "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. When the Doctor and Amy get involved in her latest investigation, Amy finds a way to Take a Third Option, and the loop is broken.
- The Silents (being creatures that you immediately forget the second you're not looking at them) induce this in their victims, with the very fact of their existence being the constantly forgotten revelation in their first episode. The problem of forgetting them cannot easily be solved; even pictures of them get forgotten instantly and spoken information about them fades fairly quickly (though not instantly), but people can leave themselves messages and warnings about them, and thus make themselves aware of their existence even when they can't actually remember them.
- In "Asylum of the Daleks", one of the warning signs that Amy Pond is losing her mind is that the Doctor tells her that he's already explained what's happening to her several times.
- In "The Inforarium", the Doctor gets a guard at the titular Library of Babel stuck in one because he's left a memory-proof recording, so the guard forgets about it every time he looks away. It's not permanent, though.
- In "Heaven Sent", the Doctor is teleported into a mysterious and sinister Mobile Maze. As he explores, he finds evidence that he's not the first person to have been imprisoned there. Eventually he figures out the secret of the maze and realises that all the previous occupants of the maze were also him, and that when each had got as far as he could toward escaping, he used his death to power the teleporter and create a fresh copy of himself from the teleporter's pattern buffer, who would then start exploring all over again. This is followed by a montage showing that in each loop the Doctor gets a bit closer to escaping, until finally he wins free and the episode ends.
- In The Flash episode "Null and Annoyed", Marlize DeVoe realizes that her husband has been drugging her in order to keep her on his side. Fearful, she records a video message to herself with the truth and tries to save it under an innocuous name, only for the computer to notify her that a file with that name already exists. She is shocked to see a message similar to the one she has just recorded telling her to run. Then DeVoe appears and tells her that she always names the video the same way, implying that this trope has happened multiple times and he had to wipe her memory every time. He then proceeds to do it again.
- In an episode of Get Smart, Max gets knocked out in an injury after discovering a big KAOS scheme and a KAOS agent plays a doctor treating him who 'prescribes' instant amnesia pills. Time after time, just as Max is about to remember the scheme, it's time to take a pill, and it's back to square one.
- In an episode of Mahou Sentai Magiranger, Houka was hit with a spell that caused her to lose her memory every hour, on the hour.
- 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.
- 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.
- 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 Red Shirt, then has a Heroic B.S.O.D. 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 B.S.O.D. 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 Torchwood, the Retcon pill used by Torchwood Three to invoke Laser-Guided Amnesia can leave fragments of memories triggered by seeing forgotten things/people again. This is a plot point in the pilot where Gwen is made to forget the existence of Torchwood, only to stumble on it again.
- In Westworld, Maeve keeps having what she thinks are dreams, featuring a Westworld staff member in a hazmat suit. When she suspects her memories are being tampered with after Dolores triggers her self-awareness, she quickly sketches the figure in the hazmat suit and goes to hide it under a loose floorboard, only to discover a bundle of similar drawings from when she's done this previously.
- 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.
- In Little Busters!, Komari's memories of her older brother do this - whenever she finally finds out the truth that he died, she falls into a Heroic B.S.O.D. so bad that the only way to get out again is to repress the memories...leaving her once more a happy girl curious about dreams of a brother she doesn't know. Riki manages to break her out of the loop by forcing her to accept reality, but Komari's grandmother had a similar thing happen to her and never recovered.
- Planescape: Torment:
- The story of the Nameless One. 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.
- In the Confusion ending of The Stanley Parable, the Narrator and player find a script in a room describing a timeline of the ending itself. One event says that the Narrator forgets the events that occurred after restarting the game four times. The Narrator is savvy enough to not restart the game this time, but the game restarts on its own, causing him to lose his memory. The player can repeat the steps taken to proceed to the Confusion ending again while the Narrator is none the wiser.
- 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.
- The Maze of Many in Goblins.
- In Mixed Myth, the sphynx Tamit is actually the Anthropomorphic Personification of Enigma, which means she's destined to always be a mystery to herself. Any time she learns her true identity, she then forgets everything.
- 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.
- 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. But then, because he treats the therapist badly, the therapist orders Francine to remember everything.
- Kronk on The Emperor's 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 salt and pepper.
- An episode of Monsters vs. Aliens (2013) involved the monsters seeing something so horrific and disgusting (Coverton in his chrysalis state) that they purposely erase their memories of it. Then they all wonder why they are mysteriously missing an hour of time and investigate, ending up subjecting themselves to the same sight and erasing their memories again. Then they wonder why they are mysteriously missing two hours of time and investigate again... and again... and again. However, B.O.B. is immune to the memory erasing because he has no brain, and throughout the episode he tries to stop the rest of the monsters from investigating and re-scarring themselves. Eventually he gets so sick of the loop that he destroys the memory erasing device, telling the rest of the monsters that if he has to suffer with the memory of what they saw, then so do the rest of them.
- The Penguins of Madagascar has an episode with Private finding a bottle of "Amnesia Spray".
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 The Venture Bros., 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 and it seems to be giving the boys some whacky brain damage where they can't properly describe the color pink.
Hank: It's kind of a... "Wednesday" color?