A plot arc that was incomplete and forgotten, and then suddenly brought back out of the blue to continue the plot arc itself. This is distinct from the ContinuityCavalcade and ContinuityPorn tropes in that it's not just a ShoutOut type situation - the plot arc is resumed, essentially where it left off.

In short, what distinguishes PlotArchaeology from similar tropes is that it's not just a one-episode reappearance as a ShoutOut. Do not confuse with [[AdventurerArchaeologist an archaeology plot.]]
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!!Examples:

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[[folder: Comic Books ]]

* ''{{Comicbook/X-Men}}'': Mystique reveals her true form to Nightcrawler, who is shocked that they look very similar. She mentions his mother's name. ''10 YEARS'' (or more) later, it's revealed that she is his mother. It hadn't been even mentioned in the comics in-between those two points.
** The Third Summers Brother. In 1993, Mr Sinister casually refer to Cyclops having "brothers", then corrects himself. This arc got aborted when Fabian Nicieza left the X-titles before he could reveal the third brother was Adam-X, the X-Treme. Over the next ten years, the concept was never referred to. (Robert Weinberg thought it was Apocalypse, but also left the book before he could say so). In 2004 Creator/ChrisClaremont suddenly brought it up again, and revealed it was Gambit, but that was in an AlternateContinuity. Then, in 2006, Scott and Alex finally meet Gabriel Summers, aka Vulcan. Unfortunately, Vulcan's backstory makes it impossible that Sinister could have known about him in order to make that casual offhand reference. Fans now wonder if there's a fourth Summers brother. Or perhaps even more than that; Sinister didn't mention a number, just that Cyclops has more than just the one brother he was aware of at the time.
* ''Franchise/SpiderMan'': The true identity of the Hobgoblin. The villain first appeared in 1983; his true identity, fashion mogul Roderick Kingsley, had first shown up three years prior. His creator Roger Stern planted a number of {{Red Herring}}s but maintains- and is corroborated by other writers- that he intended Kingsley to be the Hobgoblin all along and to reveal him after a couple of years, taking advantage of the fact that Roderick had a servile identical twin that Stern managed to sneak in without being noticed. The problem? Stern was fired not even halfway through the MythArc, and subsequent writers either disliked the Kingsley idea or didn't know about it. Doesn't help that at least two characters were framed as him- Flash Thompson, and a thug named Lefty Donovan, before Ned Leeds was KilledOffForReal and then, in an AssPull, "revealed" as the "true" Hobgoblin all along because the writers had gotten tired of the mystery and decided to introduce a ''second'' Hobgoblin, mercenary Jason Macendale (hitherto a minor villain known with the alias Jack O'Lantern), who quickly and unintentionally became a BigBadWannabe. It wasn't until 1997 that Stern was invited back and allowed to wrap up the story as he originally intended it- quite remarkably, the Kingsley idea was still internally consistent to the story and caused no real plot holes (if you pay attention, at least). For the whole story in ''painstaking'' detail, [[http://www.spideykicksbutt.com/SquanderedLegacy/SquanderedLegacyTitle.html check out these essays.]]

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[[folder: Film ]]

* ''Film/StarTrekIITheWrathOfKhan'' was all about digging up a one-episode villain from the first season of the original series and answering Kirk's question about what would happen with the "seed" that the Enterprise crew planted.

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[[folder: Literature ]]

* In the ''AnitaBlake'' series, the events of book 11 resulted in the vampire serial killing group Anita was after not actually getting caught. Fans bitched and complained when the next few books didn't mention it at all, and then in Book 17 LKH went back to it and we finally get to confront the BigBad. A few other loose threads from that were also left hanging in that book and the one right after it which are still waiting to be picked back up though.
* ''Franchise/{{Bionicle}} Adventures #10: Time Trap'', from the end of 2005 revisits several issues that were left hanging in '04, six books earlier, such as the recovery of the lost Mask of Time and the Shadowed One's reaction to the deaths of two of his servants at the hands of Makuta. The Mask of Time plot was briefly continued in an online serial three years later.

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[[folder: Live Action TV ]]

* In the first season of ''Series/{{Heroes}}'', Hiro falls in love with a waitress named Charlie. It turns out she has a brain tumor and is going to die. Hiro [[spoiler:accepts that he can't save her, gets some CharacterDevelopment, and the plot moves on. Several seasons later, Hiro regrets that he didn't save her, and the arc focuses on her again as Hiro goes back in time to try and save her, but she gets kidnapped and held hostage by the BigBad.]]
* ''NewsRadio'' had a storyline where Lisa decided she wanted to have a baby with Dave. This went on for a few episodes, then was quietly dropped. In a later episode the same season, there is a brief conversation about how the moment had passed. The writers hated continuing story lines, which the network continually tried to force on the show.
* The First Evil from ''Series/BuffyTheVampireSlayer'' makes a one-off appearance in season 3. It shows up four seasons later as the BigBad. A script involving the First that they didn't use for Season 5 became the basis of one of the XBox games.
* ''Series/StargateAtlantis'': Stardrives were mentioned very briefly in an early episode and didn't become massively important until the finale three seasons later.
* ''Series/DoctorWho'' introduced River Song in "Silence of the Library" but was otherwise quickly dropped, then brought back with the Eleventh Doctor.
** It's a habit. ArcWords sometimes get planted before they're even used in a this-is-leading-up-to-something fashion. We get a briefly-seen newspaper mention of "Saxon" being ahead in the polls midway through new series season two. Nothing is said of it until "Mister Saxon" becomes a mystery figure of season three.
* In ''Series/StarTrekTheNextGeneration'', Wesley Crusher is built up as being a very special person, and it is suggested that he would do something remarkable, eventually. Then he was phased out of the show, and was gone for something like three seasons. Come the final season, the CreatorsPet returns, and the plot arc completes itself.
* At one point, ''UglyBetty'' had a plot arc about Amanda trying to discover the identity of her biological father. After a few episode, the plot disappeared with no resolution. In the show's GrandFinale, Amanda finds her father, out of the blue and completely by accident.
* In ''{{Sliders}},'' the Kromaggs were a season two MonsterOfTheWeek who got one mention in season three. Then comes a ChannelHop... and their return as the franchise BigBad.
* On ''TheWire'', [=McNulty's=] FBI buddy gives him the results of an unfinished investigation that showed Lt. Daniels was dirty when he was on the Narcotics task force. [=McNulty=] doesn't trust him for most of the first season, but eventually the men grow to respect each other. This is not mentioned again until the series finale, when now-Commissioner Daniels is forced to resign rather than be manipulated by the threat of revealing that very same investigation.
* On ''Series/BabylonFive'', much of Captain Sheridan's character arc in Season 2 centers on [[DeathByOriginStory the death of his wife]] and how he needs to let it go and move on with his life. Fast forward to the end of Season 3, and [[spoiler: Anna Sheridan shows up on B5, with a message for her husband from the Shadows.]]

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[[folder: Manga & Anime ]]

* In ''{{Durarara}}'', the slasher is mentioned early on a couple times but not addressed until much later.

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[[folder: Video Games ]]

* Quite a few minor plots in the earlier ''Franchise/MassEffect'' games come back in ''VideoGame/MassEffect3'', sometimes in unexpected ways. An entire DLC of the third game, with profound revelations about the entire setting, is a CallBack to a throwaway bit of WorldBuilding fluff text in the first game. A villain from one of the first game's DLCs can end up being recruited as an ally in the third game, and so on.

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[[folder: Western Animation ]]

* ''WesternAnimation/AvatarTheLastAirbender'': one episode introduces Bato from Katara and Sokka's father Hakoda's fleet, and suggests the kids can meet up with the fleet. When this fails, no further attempts are made to meet up with Hakoda or the fleet until the third season.
* At one point in ''WesternAnimation/SupermanTheAnimatedSeries,'' {{Brainiac}} blasts former partner SelfDemonstrating/LexLuthor with a ray that (like many instances of FamilyFriendlyFirearms) doesn't seem to hurt him much for what appeared to be intended as a killshot. Much much much later in ''WesternAnimation/JusticeLeagueUnlimited,'' we find that [[spoiler: ''that's because it actually wasn't.'' Brainy put his data inside Lex in case he was destroyed, and this backup of himself was now needed. Enter... [[FanNickname Brainithor!]]]] ThePowersThatBe have said that they'd actually planned it the day they wrote the zapping scene, they just didn't have the right opportunity to use it for a long, long time. Lucky for them the DCAU lasted long enough to do it.
* In ''WesternAnimation/TransformersAnimated,'' Porter C. Powell makes a single not-terribly-memorable appearance in the first season and it doesn't look like he's intended to return. In season two, he does... with a vengeance.
* Unicron in ''WesternAnimation/TransformersPrime'' first appears and is dealt with at the end of season 1. After being mostly forgotten for the following two seasons, he reappears to follow up on his plans in the series finale movie ''Predacons Rising''.
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