You are watching a movie, or reading a book and everything is going along swimmingly. There is an A-plot and maybe a [[TwoLinesNoWaiting B-plot]] and a [[ThirdLineSomeWaiting C-]] and [[FourLinesAllWaiting D-plot]] thrown into the mix too. While the storyline isn't too obvious, it's pretty clear that the climax is going to be with the BigBad that is the focus of the A-plot. But there is also a small E-plot, it's so small you might not even notice it, but as the story goes on, it grows and grows until the main characters are forced to completely forget about all the other problems and focus completely on this growing threat. Despite its dire sounding name, this trope can be used [[TropesAreNotBad with excellent results]]. Ergo, this might even be a ''[[{{Pun}} Benign]]'' Plot Tumor.

Compare to a PlotTumor, where the growth of one aspect above all others is unintentional, and HalfwayPlotSwitch, which is somewhat like this, but more abrupt and leads to GenreShift. See also ArcWelding. Don't confuse with the BaitAndSwitchBoss, which is oftentimes entirely unrelated to plots and subplots.

'''WARNING: SPOILERS AHEAD'''

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!!Examples:

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[[folder:Anime and Manga]]
* ''Anime/YuGiOh Duel Monsters'': The Spirit of the Millennium Ring appears as a villain from season 1 but ends up being the BigBad in the last season after other more prominent antagonists are "defeated".
* The Chimera Ant arc in HunterXHunter started off as a side story, but eventually ended up ballooning to 132 chapters and lasting ''seven years'' real time because of numerous hiatuses.
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[[folder:Comicbooks]]
* ValiantComics' 1990's revival of ''MagnusRobotFighter'' initially picked up right where the SilverAge series left off, with a decadent upper class humanity becoming increasingly dependent on robots and vulnerable to antisocial ones; the robots chafing under humanity's rule and sometimes becoming extremely dangerous; the vast slums on the Earth's surface, beneath the gleaming towered cities, where life is terrible; and Magnus trying to find a way to set things right for all three factions. It had always been a cool premise with a lot of potential, and at first the Valiant title explored it in much more depth then the original GoldKeyComics version had. ''Then the Malev Robots from space invaded,'' conquering Earth and derailing all of the above-mentioned premise. All that mattered after that was everybody fighting space robots.
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[[folder:Film]]
* The later two ''[[Film/TheMatrix Matrix]]'' movies seem to be about the showdown between the machines and free humans, but while those two sides are busy fighting, Agent Smith is busy replicating, and by the end the warring factions must agree to a truce to deal with Smith.
* Cutler Beckett and the East India Trading Company in ''Franchise/PiratesOfTheCaribbean''. The company is more-or-less mentioned in passing in the first film, before becoming much more of a threat in the following two films. By the time ''At World's End'' rolls around, the combined threat of Beckett and Jones was enough to ultimately unite the world's pirate forces, who up until then were crossing and betraying each other on a regular basis.
* The first part of ''TheBirds'' is mainly about the romance between Rod Taylor and Tippi Hedren, which ends up completely drowned out by the titular bird attacks by the end of the movie. Most people only know the film for the bird attack portion, leaving them quite confused by how long it takes to actually get to it.
* The Z-List ''TheBirds'' tribute/rip-off ''{{Birdemic}}''. The first half of the movie is a rather bland romantic comedy. The second half is a laughably bad horror movie with terrible CGI birds.
* Many people forget that the first half hour of ''Film/{{Psycho}}'' is a heist plot involving [[DecoyProtagonist Marion Crane]] embezzling money from her boss and making her escape. The entire plotline is completely abandoned once she's murdered partway through the film. The emphasis then transfers over to Norman Bates and how he's eventually captured.
* ''Film/RedEye'' starts out like a romantic comedy before revealing that the male lead is a PsychoForHire here to present the heroine with a SadisticChoice.
* In Creator/MNightShyamalan's ''Film/TheVillage'' halfway through the movie from focusing on Lucius' trying to unravel the village's secrets to Ivy going on a perilous journey to find medicine before it's too late. The village's secrets are still revealed as a result of Ivy's journey, however.
* The main plot of ''{{Stealth}}'' was about an [[AIIsACrapshoot AI fighter jet which goes rogue and attempts to start a nuclear war]] with subplots about the military contractors who wanted to figure out how it gained independence and [[TrappedByMountainLions one of the other fighter pilots being shot down over North Korea and running from the army]]. Halfway through, the AI is persuaded into giving up, making the military contractors the main plot point, before ''that'' is resolved anticlimactically so that the climax can take place in North Korea. At the very least, the way the runaway AI was [[TalkingTheMonsterToDeath talked down]] involved a big emphasis on [[ThePowerOfFriendship teamwork]], which is brought up again in the in-universe justification for the pilots breaking ranks and embarking on the rescue mission to Korea.
* ''Film/MontyPythonAndTheHolyGrail'' has a scene where a modern historian explains the setting of Arthurian-era Britain, but then has his throat cut by a passing knight on horseback. Just another absurd gag in a movie full of them, except that we see cutaways to the police investigating the crime throughout the film. They show up at the end and arrest Arthur and his retinue for it, conveniently preempting a big final battle scene that the production [[NoBudget didn't have the budget to stage.]]
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[[folder:Literature]]
* ''[[Literature/TheCulture Matter]]'' by [[Creator/IainBanks Iain M. Banks]] starts off apparently about a deposed prince gaining back his throne from the EvilChancellor on a quasi-medieval planet, while more advanced aliens manipulate things behind the scenes. Then an archaeological dig is mentioned a third of the way through the book. Then later, the heroes find something in the city. Then with maybe four chapters left, the thing they find turns out to be SealedEvilInACan, whose first act is to kill all of the characters involved in the struggle over the throne. All but one of the surviving characters die trying to prevent it from [[EarthShatteringKaboom blowing up the world]].
* Creator/TadWilliams's ''Literature/{{Otherland}}'' involves a huge number of characters, and starts off rotating between their not-immediately-connected stories. The serial killer Johnny Dread is among this cast but doesn't play a particularly prominent role in the first volume. However, he grows in power and significance to be the main antagonist that everyone is fighting at the climax, even overshadowing the creator of the virtual world they're in.
* ''Literature/PerdidoStreetStation'' by Creator/ChinaMieville starts off looking light - the A plot is going to be a scientist helping a bird man to fly again, with a B plot of his girl friend making a sculpture for a mysterious crime boss. But then one of the caterpillars the scientist was studying hatches and starts {{Mind Rap|e}}ing everybody. Everything else gets pushed to the side when it turns out that the moth is just about the deadliest thing in the world.
* ''Literature/TheNightsDawnTrilogy'' by Peter F. Hamilton (especially book 1) seems to be about smuggling, politics, and revenge. That is until, half way through the first book, out of left field, the dead come back to life.
* [[HordeOfAlienLocusts The Vord]] from the ''Literature/CodexAlera'' series are a classic example of this. They're introduced in the first book as the nasty but apparently unintelligent and unimportant guardians of the MacGuffin of a SideQuest. In the second book they prove to be ''very'' intelligent (though only collectively) and become a major threat, only to apparently be completely wiped out. In the fifth book, they're back with a vengeance, having been building up their forces massively in the background and forcing [[TheHero Tavi]], [[WorthyOpponent the Canim]] and [[MagnificentBastard Lord Aquitaine]] to team up to stop them.
* The ''entire'' ''LordOfTheRings'' trilogy essentially springs from a minor plot point (the ring) in ''Literature/TheHobbit''.
* In ''Literature/ASongOfIceAndFire'' The Night's Watch and their undermanned defence of the Wall initially seems, compared to the epic civil war in the South, like a pretty minor plot which we're only seeing because the son of a main character is up there. It gets a bit more interesting when the Others show up, but the sheer world-endangering EldritchAbomination nature of their threat is only gradually revealed to the reader, and is still unknown or unappreciated by the vast majority of the characters. It takes the reader from rooting for whichever claimant they ''like'' the most to which one seems most able to defeat the BiggerBad.
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[[folder:Live-Action TV]]
* While fans will [[FanWank debate]] endlessly about whether Creator/JossWhedon was winging it or not, most ''Series/{{Buffy|the Vampire Slayer}}'' seasons are good examples, particularly season 6. The BigBad [[NotSoHarmlessVillain looks like]] it's three fairly {{Harmless Villain}}s. But there's a subplot about Willow being addicted to magic, which is fairly minor at first, but by the end of the season, one member of the trio has been flayed alive, and everybody is too busy trying to prevent Willow from destroying the world to care about the two others.
** Seasons 2, 3 and 4 also show this pattern: a bunch of threats at the beginning of the season that end up being eclipsed by some bigger one.
*** Season 2 had the most rational explanation that there wasn't really a singular Big Bad throughout the season until [[spoiler:Angel [[MagnificentBastard went evil]]]], and once he did, everything else paled in comparison for the rest of the season...and maybe even for the rest of the series.
*** Season 2 also had to switch gears near the start because over the summer between seasons 1 and 2, the actor who played The Anointed One had grown too much to believably have him as the same unaging child vampire. The Anointed One was going to be the Big Bad of season 2.
* The 2000-era ''Series/{{Battlestar Galactica|Reimagined}}'' drew most of its plots from conflicts between humans and Cylons, infighting within the fleet, and the overarching MythArc of finding a way to Earth. Along the way, however, seemingly minor details come up about the titular [[TheBattlestar warship]]:
** The miniseries establishes that she's old and about to be decommissioned.
** Battle damage accumulates on the hull as the series goes on.
** A third-season episode involves a malfunctioning airlock threatening lives, along with remarks on how ''Galactica'' would be in need of a major overhaul under normal conditions.
** A similar remark about equipment malfunctions occurs the next season.
** Finally, it is revealed that ''Galactica'' has started to fall apart from all the wear and tear over her many years in service, and the last few episodes of the series see many plots put on hold as the ship's critical condition begins to dominate the series.
* In Season 4 of ''[[Series/TwentyFour 24]]'', the raid on the Chinese embassy doesn't seem like a big deal at first, but wait until the end of season 5.
* The Kromaggs from ''{{Sliders}}'' grew from a a semi-recurring menace into the series' BigBad. It had little to do with the original premise and was relatively poor-received.
* Kirsten Cohen of ''TheOC'' drank on-screen enough for TelevisionWithoutPity to have started a "Kirsten Cohen drink watch '03." But at the end of season 2, she immediately switched from frequent wine drinker to inst-alkie complete with {{Wangst}}.
* In the last half of season two of ''Series/BlakesSeven'' Travis has been court-martialed by the Federation and is just as much a wanted man as Blake. Initially he cooperates with Servalan covertly, but by the penultimate episode he hints he's got a new agenda, which is fully revealed in the season finale and forces Blake to abandon the goal he's been attempting to achieve all season.
* The second season of ''TrueBlood'' is mostly about Sookie helping Eric and the Dallas vampires find the missing sheriff, Godric. Meanwhile, there's a subplot going that has Tara moving in with a social worker who is secretly a maenad. For most of the season, the maenad, Maryann, isn't really much of a threat; she mostly just prances around holding sex parties and trolling Sam, committing a couple of murders while she's at it. However, after the Dallas plot is wrapped up, Maryann becomes the BigBad and the main cast must team up to [[spoiler:save the townspeople's souls from her control and stop her from killing Sam in a ritual sacrifice.]]
** In the book season two was based on, the Maryann character shows up in one scene near the beginning, then Sookie (being the first-person narrator) takes the story with her to Dallas. When she comes back to deal with the maenad in the climax of the novel, readers might be forgiven for forgetting she was ever there in the first place. It's especially aggravating because in the book version the problem is resolved when [[spoiler:the maenad kills the people she came to kill, then moves on to menace some other town.]]
* In ''Series/DoctorWho'''s third (revived) series, the entire plot of Utopia and the plight of humanity becomes negligible when a certain tenacious character makes a surprise return. [[spoiler: Or so you think. In the next couple of episodes, just when you've gotten used to the idea that the certain tenacious character is the big threat, it turns out that we aren't quite done with the far-future plight of humanity -- and they aren't quite done with us...]]
* ''Series/{{Lost}}'' is naturally a big offender here. Just a small spoiler-free [[spoiler:(not)]] hint: The Final Season [[spoiler:and the two that preceded it]] is not really about castaways trying to survive after the crash and to get off the Island anymore.
* ''Series/{{Dexter}}'' Season 7: For the majority of the season, the focus is on Hannah [=McKay=] and Isaak Sirko, both jostling for position as Dexter's main antagonist. Meanwhile, in the background, Maria [=LaGuerta=] investigates the accusations levelled at her late friend and former lover, James Doakes. Come the final episode, [[spoiler: Isaak's dead, Hannah's in jail, and Maria's figured out who the REAL Bay Harbor Butcher is.]]
* In ''[[Television/BabylonFive Babylon 5]]'', mysterious alien vessels are introduced about halfway through the first season. Their first appearance is in the appropriately named episode ''Signs and Portents''. We don't even learn the name of the race that uses these strange-looking ships until after a few appearances. As the series progresses, we slowly learn more about them, until by the time Season 3 rolls around, the Shadows have become the series main antagonist, and the show's MythArc is in full swing.
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[[folder:Music]]
* Played for laughs in "Jack Sparrow" by TheLonelyIsland. The song was supposed to be a generic club rap with a hook by Michael Bolton. Turns out said hook was Michael Bolton singing a chorus about [[Franchise/PiratesOfTheCaribbean Captain Jack Sparrow]] which more or less takes over the song. He switches it to ''Film/ForrestGump, Film/ErinBrockovich'' and finally ''Film/{{Scarface 1983}}'' by the song's end.
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[[folder:Toys]]
* ''{{Bionicle}}'' web serials tend to choose this route. More often than not, they set up a basic plot-setting, and either shove it aside or wrap it up within the first couple of chapters, to concentrate on something barely related. Sometimes, these plot threads connect, other times, they just sort of get forgotten.
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[[folder:Videogames]]
* A subplot about Alchemiss' power increasing in ''[[FreedomForce Freedom Force vs. The Third Reich]]'' takes over the third act of the game, as Alchemiss [[WithGreatPowerComesGreatInsanity goes insane]] and nearly destroys the universe.
* In the ''VideoGame/{{Marathon}}'' trilogy, an evil [[SealedEvilInACan trapped inside the sun]] since forever is briefly mentioned once in a short piece of religious text of an alien planet in the second game, for the purpose of fleshing out a cultural {{backstory}} for the game's real plot. [[spoiler:Or so you think until it turns out that the "religious texts" were actually [[OhCrap accurate historical recordings]], and the enemy's eventual attempt to destroy the sun (with a likewise briefly mentioned WMD) releases the chaos god. The entire third game revolves around putting it back.]]
* The evil organizations in all of the ''{{Pokemon}}'' games come into play as extremely minor obstacles in the way of the player's true quest (which is ToBeAMaster and GottaCatchEmAll), but swell in importance, numbers, and ferocity as the player progresses, and eventually eclipse the original quest in importance (at least for a little while).
** The fifth generation games, as some feel, was the first generation to avert this, by basically having the plot involving the evil organization introduced in the first town you visit and remain important throughout the entire game.
*** Well, only if you believe that ''Colosseum'' didn't try for it first - you don't even get far from Pyrite before you realize Cipher is SeriousBusiness.
* In ''UltimaIII'' the Great Earth Serpent was just an obstacle guarding the entrance to the Big Bad's castle, which you needed a password to get by. In ''Ultima VII Part Two: Serpent Isle'' you learn that the serpent in question was a cosmic force of balance, and removing it from its proper place threatens to destroy the entire universe as the serpents of Chaos and Order struggle unchecked.
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[[folder:Webcomics]]
* ''Webcomic/SluggyFreelance'' Dr. Schlock's evasion of Heretti-Corp dated back to when he was forced to work for them, and even when hC became the main plot, Schlock was still a minor supporting character. His fugitive flight from them took over more and more panels until "broken" [[spoiler: when he took over Heretti-Corp.]]
* Initially, ''Webcomic/CollegeRoomiesFromHell'' focused on three very different losers trying to live together while occasionally dealing with wacky supernatural baddies. At one point, TheDevil showed up, grabbed a character's soul and then was quickly dispatched. The devil is mentioned another couple of times, but doesn't appear again for a while. Then, it turns out one of the characters is a pawn in his plan to destroy the world, and all the other characters join forces to stop him.
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[[folder:Western Animation]]
* The ''FamilyGuy'' episode ''Da Boom'' features half-octopus Stewies multiplying out of control and eating most of the characters.
** "[[SuspiciouslySpecificDenial We don't know that they ate them!]]"
* The first episode of Season 14's "Coon & Friends" trilogy in ''WesternAnimation/SouthPark'' was about Cartman trying to get Captain Hindsight to join his superhero team, with BP's recurring drilling accidents being the B-plot. Then BP unleashes Cthulhu and the last two episodes focus mostly on him, tying up Captain Hindsight's story in the second.
* ''TheSimpsons'' loves this trope, a good example is ''A Tale of Two Springfields''. It starts off being about a badger infesting a dog house, but when Homer tries calling animal control, he gets distracted by the fact that the area codes have changed. The badger looks through a window growling menacingly, but Homer shrugs it off, saying there are more important things to deal with now. At the end, when all of Springfield is focused on the resolution of the episode's major plot, and an army of badgers seize the opportunity to take the town by surprise.
* In ''WesternAnimation/{{Futurama}}: Bender's Game'' the titular game starts as Bender tries playing an RPG and his imagination goes overboard. However, this is but a loosely connected sidestory to the main plot about dark matter (fuel). Then, right as that plot is reaching its climax, the messing with quantum physics caused the dark matter Bender had on his person to suddenly get sucked into his fantasy.
* ''FairlyOddParents'': For most of the "Wishology", the [[TheDragon head]] of the MechaMooks was simply a recurring opponent. However, after seemingly falling into the background, he suddenly goes [[EnemyCivilWar rogue]] and [[YouWillBeAssimilated absorbs the entire planet]]. With the revelation that [[spoiler:DarkIsNotEvil]] he proves the trilogy's true BigBad. Considering all the parodies in said films, he is likely a direct ShoutOut to [[Film/TheMatrix Smith]].
* ''{{Spider-Man the Animated Series}}'': we get a double whammy, First with the portal machine that a [[MonsteroftheWeek Villain of the Week]] built, and the Carnage Symbiote, who is really only fought once or twice in the series. Not only is it used to [[spoiler: "Kill" Mary Jane]] but the final battle of the show involves [[spoiler: Carnage coming out of nowhere and trying to use the machine to destroy the entire multiverse.]] The WordOfGod supposedly says that a reason the show ended with an unresolved plot was that after [[spoiler: Saving all existence]] they couldn't think of anymore compelling plots for the webhead.
* In the first season of ''WesternAnimation/AvatarTheLastAirbender'', [[AntiVillain Prince Zuko]] is initially the main villain, while the other major recurring villain, [[SmugSnake Commander Zhao]], is mostly just his far less sympathetic rival. Midway through the season, however, Zuko has started to get CharacterDevelopment shifting him towards AntiHero territory (though he doesn't fully get there until the second season) while Zhao gets promoted to Admiral, letting him take over as the main villain in time for the SeasonFinale.
** Also, while [[BigBad Fire Lord Ozai]] is identified as the other half of [[TheHero Aang's]] inevitable UltimateShowdownOfUltimateDestiny pretty much from the start (albeit in a BiggerBad OrcusOnHisThrone sort of way,) the first season contains one brief shot of a rather sinister looking girl, who is then identified in TheStinger as Zuko's sister. She is not named, doesn't speak until Season 2, and seems to serve no purpose beyond looking a bit creepy. The girl is [[MagnificentBitch Princess Azula]], who may technically be TheDragon to Ozai, [[HeroKiller but is so competent in that role]] that they sometimes appear more like a BigBadDuumvirate, and she remains a very serious threat even after Ozai himself takes an active role.
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[[folder:Other]]
* In the ''MarsAttacks'' bubblegum cards series, the Martians invade! And they release [[BigCreepyCrawlies giant bugs]] to mop up humanity! And then ''disappear'' for most of the cards, as all but ''two'' deal with the giant insects until humanity suddenly decides to attack Mars for the last five.
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