An installment in a series begins with a radical change to the status quo that the characters don't seem to notice or comment on.
Say you're watching your favorite TV show. All of a sudden, and usually at the beginning of an episode, something happens - a character who died is now alive, or the setting is completely different. Something is obviously up here, and you can't wait to see how the characters react. But then, they don't. It's not that they don't notice this change, but it's treated as if it's completely normal.
This could be anything from a Dream Sequence to an Alternate Universe. The point is, the audience doesn't know what's going on because the characters are, at first at least, treating this interlude as a completely normal occurence. Like In Medias Res, the audience only finds out what is happening later on. Compare Elephant in the Living Room, when characters aren't talking about it but do notice, and contrast Ripple Effect-Proof Memory. When a timeline has been changed, everyone who doesn't have a Ripple Effect-Proof Memory is covered by this trope. Examples of that trope don't have to be added here.
- The "Endless Eight" arc in the Haruhi Suzumiya anime was like this during the beginning of the "Groundhog Day" Loop.
- The aborted anime Usagichan De Cue has Mimika, a bunny-girl formed from skilled fighter Mikami Inaba merging with a pet rabbit. When Mimika appears in the home of Haru, the rabbit's keeper, nobody seems surprised, not even noticing that Mimika has rabbit ears and a powderpuff tail. Mimika explains that she can project thought control similar to a Perception Filter, so that people regard her as perfectly normal.
- Ushio and Tora: Towards the end of the series, the Hakumen causes Ushio's existence to be entirely forgotten. Every human character meets him for the first time, and are quite angry at the familiarity he displays with them. Even one of Ushio's father's allies doesn't recognize him, saying he never had a son. Fortunately, it turns out Tora still remembers him, and together they end the curse.
- Wanted: At some point every supervillain banded together to rewrite reality so that not only did the world forget superheroes were real, the superheroes forgot as well (the supervillains, for their part, operate in secrecy). One villain killed his nemeses (Batman & Robin expies) by dunking them in a vat of acid, they kept screaming that they weren't superheroes, they'd just played them on TV.
- Emperor Joker: The comic starts with Superman as a dangerous criminal locked up in Arkham Asylum and trying to escape Bizarro's clutches every day, Lois Lane as a bald Corrupt Corporate Executive, the Justice League as a bunch of supervillains and the actual DC supervillains as a rag-tag bunch of heroes, all treated as if this is the natural state of things. It's only revealed halfway through that all of reality has been perverted by The Joker after he acquired the powers of Mr. Mxyzptlk, which only those two characters are initially aware of.
- In Robert Sheckley's Mindswap, the ending is the protagonist getting his body back in a parallel dimension, and then doubting whether he's back in his own universe, or still in a parallel one. He checks carefully, but... no. Same three red suns, same egglaying mother.
- Ursula K. Le Guin's The Lathe of Heaven. When Reality Warper George Orr has an "effective dream" and changes the world, no one remembers what the original world was like except him and anyone who was present when he had the dream.
- Animorphs: Megamorphs #3's first chapter ends with the Wham Line about people owning slaves, with nobody seeing a problem. It gets worse from there, with Rachel nowhere to be seen, Jake being a egomaniac asshole considering selling out Cassie to the government for disapproving of American imperialism, and writing off entire chunks of humanity called Primitives. When the Drode restores their memory to the real timeline, they retain the branch timeline's memories and feel sick to their stomachs. For the rest of the book they have Ripple Effect-Proof Memory, but retain the memory of what will happen if they fail.
- Isaac Asimov's "Gimmicks Three": After Welby goes back in time, his contract disappears, and Shapur, the demon, doesn't understand why. To get an explanation, they restore his memory of the original timeline and Welby happily brags about the escape clause he discovered in the contract.
- William Tenn's "Brooklyn Project" ends with an official demonstrating that the time travel experiment had changed absolutely nothing... except that the reader is fairly certain that neither him not the audience were Blob Monsters when the demonstration started.
- Buffy the Vampire Slayer:
- In the episode "Superstar" even the credits are changed to show the change of a spell that makes Jonathan into a Black Hole Sue.
- The first episode of season 5 introduces Dawn, Buffy's younger sister who didn't exist before this episode. Everyone (including Buffy) remembers Buffy as always having a younger sister.
- Stargate SG-1: "The Fifth Man" starts with the team in a crisis situation, with only 3 of the team's members able to escape, and the other two trapped on the other side of the gate. Except that the team only has four members.
- "My Heart Will Go On" features a fallen angel going back in time and changing the timeline, preventing the Titanic from sinking, and causing all sorts of ripple effects. Sam and Dean are blissfully unaware that they're living in an altered timeline until they discover it over the course of the episode.
- Another episode has Sam & Dean Winchester leading completely different lives as unrelated people Dean Smith and Sam Wesson, an executive and an IT guy working at the same firm who get sucked into a supernatural mystery. Turns out it's a ploy by some angels.
- The episode "Nihilism" opens with Dean owning a bar alongside Pamela Barnes, despite her being dead for a decade at that point (and for that matter, she can see, despite having been blinded some time before her death). When a quick sequence of events involving the two of them play out repeatedly, it quickly becomes apparent that Dean's stuck in a Lotus-Eater Machine, placed there by Michael after being possessed by him at the end of the previous episode.
- One episode of the Weird Science sitcom (based on the movie) starts with Gary and Wyatt getting bullied which they're used to, but they seemingly have no knowledge of Lisa. They then discover evidence of her existence and look into her. It's later discovered they told a classmate about Lisa and the classmate made Lisa her slave. One of the first things she did was wish Gary and Wyatt forgot about Lisa.
- Star Trek: The Next Generation:
- The episode "Yesterday's Enterprise" opens with the Enterprise-D coming upon a time rip with the Enterprise-C (lost decades earlier) emerging. Suddenly, reality is changed and the Federation is now involved in a war with the Klingons. On top of that, Tasha Yar (killed in season one) is still on the bridge crew. No one notices anything is different, although Guinan suspects something is wrong.
- The episode "Conundrum" has an unknown alien ship cause a bit of Laser-Guided Amnesia on the crew and alter the computer records of the ship to make the crew think they are at war with another alien race called the Lysians, who are enemies of the race that screwed with their minds. For good measure, they also have a member of their race infiltrate the crew and pretend to be the Number Two. Everyone is initially caught in the ripple, but Picard eventually does some Spotting the Thread.
- In Torchwood, the episode "Adam" starts off with with a new (to the viewers) team member Adam in the opening credits who's supposedly been with the team for the last three years. Turns out he's an alien who's infiltrated them by inserting years of fake memories into the Torchwood teams' minds.
- BlazBlue: Central Fiction: from the beginning of the game, the game somehow seems to revert the timeline and events to that of the first game, i.e. 2199. Most people act like they would during that part of history. There are a few people, however, who notices something's wrong. It's revealed later that the world they're in aren't the same world they (or the audience) know, but rather a Pocket Dimension called "Embryo", and most people's memories are reverted to the events of the first game. They do, at least, regain their memories around the end of the second act.
- In Dishonored 2, if you somehow manage to restore Aramis Stilton's sanity by manipulating the past, he will join you on the Dreadful Wale in the next mission, acting like he's been your ally all along — which he has, in this new timeline. What's more, Meagan Foster also suddenly has a right arm, which she had lost in your original timeline while trying to discover what happened to Stilton. Nobody except the protagonist (Emily or Corvo) notices the changes, however, since only the protagonist (and the Outsider) have Ripple-Proof Memory.