-->''"I know I'm human. And if you were all these Things, then you'd all just attack me now, so some of you are still human."''
--->-- '''R.J. [=MacReady=]''', ''TheThing''

-->''"Listen Jim, we've got to have codenames for them. D'you remember the nursery rhyme "Tinker, tailor, soldier, sailor"? ... All I want from you, Jim is one... one word. Just ONE codename. If you have to scrawl it on the front door of the Embassy in Prague or phone our resident hood and shout it in his ear before you go underground... if there's some kind of fumble and that's necessary... just give me that one word."''
--->-- '''Control''', ''[[JohnLeCarre Tinker, Tailor, Soldier, Spy]]''

Our heroes are sent to a conference, retreat, or some other gathering with a group of colleagues they don't know personally. Only... one of these "colleagues" is not what they seem.

Our heroes soon learn that one of their party has been replaced by some manner of villain (typically TheMole, though a random escaped criminal is not unheard of), but, for various contrived reasons, that's all the information they're going to get. So it's up to them to work out which of their supposed colleagues is really TheMole before he can kill them all. And [[HangingSeparately you can't trust anyone until you do.]]

Often results in everyone being LockedInARoom. This can be self-imposed, as our heroes can't chance TheMole reporting back to headquarters. Circumstances will always contrive to prevent our heroes from getting in touch with the outside world to find out who TheMole is.

Non-recurring characters are subject to being killed off one-by-one by TheMole. The heroes are sometimes exempt, as TheMole needs them to get out of the Locked Room.

In a well-done example, the audience will work out who TheMole is only seconds before the heroes do, though they'll typically be led to an [[RedHerringMole incorrect guess]] from early on.

Strictly speaking, no one is above suspicion, even our heroes, and at least one member of the group will panic, accuse the heroes, and run off to a certain demise. Of course, the audience (usually) knows better.

However, there are some rules to guide you in making your short-list of suspects:
* One person will seem to actively hinder the investigation. He'll drop the radio, breaking it just before a description of TheMole is broadcast. He'll have a panic attack at a critical moment endangering the group. He'll be suspiciously uninformed about whatever his job is supposed to be. This person is ''never'' TheMole. [[RedHerringMole He's just an idiot.]] (See HanlonsRazor.)
* One person knows his job well, but he's a little high-strung. He accuses a lot of people of being TheMole on shaky grounds. If it doesn't turn out that ''he's'' the Mole (which is a little too obvious, and therefore rare), odds are the real Mole's going to kill him.
* One person is very competent and helpful. He'll even have some extra skills that are handy for just the room in which they are locked. He might even find clues as to TheMole's identity. At some point, he'll save the hero's life. He's TheMole, and he's really very good at it.

Common twists:
* The idiotic RedHerringMole turns out to be a spy for the good guys. He's been keeping it a secret since, like everyone else, [[HangingSeparately he's not entirely sure that TheMole isn't one of the heroes]]. His apparent incompetence is really ObfuscatingStupidity, and he's trying to goad the ''real'' Mole into tipping his hand.
* There's a ''second'' mole -- perhaps even one that the first mole doesn't know about.

Uncommon twists:
* ''None'' of them are TheMole: the initial message was a fabrication by the bad guys to make [[HangingSeparately the heroes turn on each other]].
* None of ''them'' are TheMole: the hero has been hypnotized to act as mole [[ManchurianAgent without even his own knowledge]], or is simply an UnreliableNarrator.
* TheMole sucessfully frames someone else.

Compare SpotTheImposter, ZombieInfectee, AndThenThereWereNone, WitchHunt, and RedHerringMole.
----
!!Examples:

[[foldercontrol]]

[[folder:Anime]]
*YuYuHakusho has one of these just after the Dark Tournament arc, but Yusuke receives no tells to help him figure it out. The Mole can perfectly copy the appearance, personality, memory, etc. of whoever he touches, and he's impersonating [[GenkiGirl Botan]], [[JerkWithAHeartOfGold Kuwabara]], [[CunningLikeAFox Kurama]] or [[NobleDemon Hiei]]. The only way to break his powers is to knock him out. Yusuke starts out by asking various questions only the real character would know, but this is subverted. He asks for Kuwabara's birthday, but Kuwabara points out that Yusuke doesn't even know when his birthday is is in the first place; Kurama "helps" by giving much more information than asked for, for example: "What's your mom's name?" nets "Shiori Minamino, she's forty years old and is set to be married again in the fall;" Hiei refuses to answer his question ("What's your sister's name?") at all, because Yusuke knows damn well, which, to his dismay, Yusuke realizes ''is'' exactly how Hiei would answer; finally, he attempts to BluffTheImpostor by asking Botan her "three sizes," reminding her about that time on the school roof, but Botan calls the bluff. [[spoiler: Yusuke eliminates Hiei and Kurama because they are too skilled to be caught (which is ironic enough for Kurama to comment on, because Hiei ''had'' been caught earlier), then eliminates Botan because there's ''no way'' these {{Mooks}} would beat on the only non-combatant--but, aware that there are flaws in his deductions, the clincher is really that Kuwabara's the only one he wouldn't feel guilty about knocking senseless!]]
** For the record, he was right.
* The anime TheyWereEleven uses this: As a test, ten students must survive on a derelict space station...so why are there eleven of them?
* Lots of cases of [[http://tvtropes.org/pmwiki/pmwiki.php/Main/DetectiveConan Detective Conan]] use this trope.
* [[http://tvtropes.org/pmwiki/pmwiki.php/Main/HayateTheCombatButler Hayate no Gotoku]] uses this sceneraio in it's parody of [[http://tvtropes.org/pmwiki/pmwiki.php/Main/DetectiveConan Detective Conan]] in the manga. In the anime it's a different setup.
[[/folder]]

[[folder:Film]]
* The '80s version of ''TheThing'', and the short story both versions were based on, ''Who Goes There?'' both combined this trope with TheVirus.
* Another alien-invasion movie example: ''[[http://www.imdb.com/title/tt0133751/ The Faculty]]''; the humans who have not (yet) been taken over by alien parasites regard each other with suspicion and must figure out who in their number has fallen under alien control... but more than that, they must determine which person has actually been an alien all along. Not really susprisingly, the one who is an alien rather than an alien-controlled human is [[spoiler:the "new girl," who has been giving the other students a backstory they've had to take on faith, rather than having a known history in their community.]]
* ''Identity'' is a variation of this. 10 strangers meet in a remote hotel, where they start getting killed one by one by a killer, who is presumably one of them. At first the trope seems to be played straight, as the helpful, authority figure cop is revealed to really be a criminal and a killer. However, at the end, it's revealed that ''the'' killer who was actually killing the guests was [[spoiler: the little boy. This makes sense because the characters are all personalities inside the mind of a serial killer with multiple personality disorder; the little boy is the murderous personality, representing the abuse the killer experienced as a child]].
* ''D-Tox'' was a film with this premise, starring Sylvester Stallone. Stallone was one of 9 cops being treated for psychological problems at a remote ranch in snowy Wyoming. However, one of the other patients was actually a serial killer who targets cops, having killed the real patient and assumed his identity. I forget the specific identity of the real killer, except that he turned out to be the character who was most apparently helpful and mature (as opposed to the cowardly guy or the violent alcoholic).
* ''{{Mindhunters}}'' was another film with this premise, about several FBI students being trained as criminal profilers at a remote training facility. One of them is actually a serial killer killing the other characters off one by one. Of course, the killer turns out to be [[spoiler: the heroic, helpful, supportive Alpha Male of the group]].
** The killer was also a [[spoiler: SelfMadeOrphan]], a backstory detail which should have really tipped them off a lot sooner.
* In the comedic Movie-Based-on-a-Board-Game ''Clue'', this is essentially the premise of the entire movie.
[[/folder]]

[[folder:Literature]]
*Possibly the ultimate literary example; Agatha Christie's AndThenThereWereNone, a.k.a. ''10 Little Indians''. The Mole is [[spoiler:the only innocent character. And that's all you're getting. Read the book.]]
** Also the plot of Christie's ''The Mousetrap'' and the play that was made from it. The mole in this one is [[spoiler: ''one of the canonical secrets of the theater industry.'' Go see the play. It's a fun one.]]
* In the ''StarTrek'' novel ''Kobiyashi Maru'' this was a training scenario for Starfleet cadets. Several dozen cadets were dropped on an abandoned moonbase, and told that one of them was TheMole. Their teachers then sat back and watched what the cadets did. Typical behavior was to band together into small groups, and end up fighting against other groups because one of them could be TheMole. Chekhov's solution was to simply kill EVERYONE (at the end of the training, all his victims assumed he was the Mole. He thought he was the winner. The teachers explained he was simply a very skilled assassin (and a bit of an idiot)). Turns out there was no Mole, the scenario was designed to emphasize the dangers of distrust and paranoia. He was then told that his hero, a young captain named Kirk, had come up with a working solution; he invited all groups to join his, but the condition for joining was that everyone would be disarmed. The exception were two guards selected by Kirk; if one of them happened to be TheMole, the other could just shoot the guy.
* In Maurice Leblanc's first published Arsène Lupin short story, ''L'arrestation d'Arsène Lupin'', the passengers of a transatlantic liner learn by telegram that the famed GentlemanThief is travelling in first class under an assumed name. All they know is he is blond and his fake name begins with R. The story deals with the idle young nobility on board trying to unmask him from those clues while various precious objects are stolen around them ; until the ship arrives and Lupin is revealed as [[spoiler: [[TomatoSurprise the narrator]], who was not blond and whose name did not begin with R, but who planted false clues to mislead the police]].
* Used to some extent in ''{{Dune}}'', with a letter throwing transparently false suspicion on Jessica. No one in House Atreides suspects Yueh of being TheMole at all, though he's already been identified as such in the narrative.
** Maybe the fact that in the Dune universe, "Do No Harm" took the form of unbreakable psychological conditioning had something to do with it...
* A major plot thread in the second ''{{Mistborn}}'' book-it appears for much of the book that one of the main characters has been replaced by a kandra, a creature that can consume a corpse then animate it and imitate the person in question almost perfectly. Despite assistance from her own kandra, it takes Vin most of the book to figure out who it was. As was stated on the main Mistborn page, TheReveal is quite brilliant.
* Subverted in ''TheDresdenFiles'' book ''Dead Beat'', where Harry quickly and [[InTheBack decisively]] identifies the current body of [[BodySurf the Corpsetaker]] within seconds of his/her/its body-hopping.
[[/folder]]

[[folder:LiveActionTV]]
* ''MacGyver'': "The Invisible Killer". Just as Mac determines which of the Phoenix employees on his wilderness stress-relief retreat is an imposter, we find out that not one but ''two'' of them are really escaped convicts.
* ''TheTwilightZone'': "The Monsters Are Due On Maple Street". A street in a small town loses all power and use of their cars. Spurred on by a young boy's claims that this is a common comic book plot, they quickly suspect each other of being aliens. As riots break out, the audience learns that, no, none of the folks on Maple Street are aliens. The whole thing was set up by alien puppetmasters outside of town to trigger the riot, who comment on how easy conquering Earth this way is. Replace "aliens" with "terrorists" and "alien puppetmasters" with "US Army researchers", and you get the version used in the 2002 remake.
** The episode "Will the Real Martian Please Stand Up?" had a diner full of suspicious patrons who suspect each other of being a possible alien hunted by the police. The twist here is [[spoiler: after one of the patrons reveals himself to be an alien scouting for a Martian invasion, the cook at the diner turns out to be ''another'' alien, who informs him that his fellow Venusians have beaten the Martians to the punch.]]
* ''FirstWave'' did this numerous times and in every variation. They added the further complication that the hero himself was usually ''also'' an imposter in the group, and had to spend much of the episode convincing the others to trust him.
* ''[[Series.WarOfTheWorlds War of the Worlds]]'' also did a number of variations on this. The most straightforward instance was "The Last Supper", complete with the undercover spy who initially appears to be a shoo-in for TheMole.
* ''The Mole'' implemented this concept as a Reality-based GameShow. Thought the show the contestants are faced with several challenges which, if completed successfully, earn money that goes to a global pot. However, as the name indicates, one of the contestants is a Mole hired by the producers to make sure they win as little money as possible. Contestants are eliminated via a quiz at the end of each episode that asks several bits of biographical information about the Mole: the person who gets the least amount of questions right is eliminated.
* The second season of ''WhoWantsToBeASuperhero'' included such a challenge. Given that there were ''two'' actors planted amidst the first season contestants (both TheMole and a scheduled FaceHeelTurn), this was a believable threat for the heroes and the audience. [[spoiler:But it turned out to be a false one; all the contestants were for real this time, and Stan just wanted to see if they'd go into witch-hunt mode.]]
** ''StarTrek'': In the episode Allegiance, Picard found himself in a similar situation to the Star Trek novel example, where he and three strangers are left in a cell with hints that one of them is working for their captors. In this case, not only was one of them the mole, but an impostor Picard was also placed on the Enterprise to run an experiment on the crew.
**And during the "Dominion War" arc of [[StarTrekDeepSpaceNine DS9]], the Founders pull a version of the "Monsters on Maple Street" ploy; a few of them infiltrate the Federation and its allies, leak information that there are shapeshifting moles in place, and watch their enemies tear themselves apart.
* Subverted in an episode of ''Monk''. After breaking into a woman's home to find her being drowned by her identical twin, Lt. [[TheDitz Randy Disher]] asks which one the real one. [[DeadpanSnarker Captain Stottlemeyer]] suggests arresting the one that ''wasn't drowning.''
* In the season 6 opener of {{NCIS}}, we learn that [[spoiler: Agent Lee]] is TheMole, but the team thinks it is [[spoiler: Agent Langer, who Lee frames and then kills]]. Later, they figure it out and it ends in [[spoiler: RedemptionEqualsDeath]].
* On WMACMasters during a Dragon Star match between Hakim “The Machine” Alston and Ho Sung "Superstar" Pak someone wearing a ghost town ninja outfit eliminated both of them and the other masters figured out early on that one of them had to be the masked ninja. They suspected the maters who had not been seen that episode like Mike "Turbo" Bernardo and Ho Young "Star Warrior" Pak as the culprit and eventually put Star Warrior (who is the [[CainAndAble older brother]] of Superstar) on trial for it with Tiger Claw and Olympus acting as lawyers and Turbo as Judge. He was found not guilty after the glove Tracer clamed the mask ninja dropped did not fit (so they must acquit). It turns out the masked ninja was Warlock who had secretly joined the evil cult called Jukido and was trying to steal the Dragon Star
* [[http://tvtropes.org/pmwiki/pmwiki.php/Main/Sanctuary Sanctuary]] has a particularly difficult one to solve. They do figure out who it is, but only the main characters survive until then.
[[/folder]]

[[folder:PartyGames]]
* This is the entire idea of the psychological party game [[http://en.wikipedia.org/wiki/Mafia_%28game%29 Mafia]] (also known as Werewolf, also known as Witch Hunt), although generally about a quarter of the players are TheMole.
[[/folder]]


[[folder:Theater]]
* In the play ''But Why Bump Off Barnaby?'', Barnaby claims that one of the guests isn't who he seems, and even manages to write part of the person's name before dying. Of course, most characters have those three letters in their name.
[[/folder]]

[[folder:VideoGames]]
* In [[TheElderScrolls Morrowind]], a book titled ''A Game at Dinner'' tells the story of a sadistic ruler inviting his advisors to a feast, ending it with a large stew and a message: he's poisoned those he suspects to be spies in a way that the spy protagonist did not expect, and the antidote for the poison is in the stew. Each spy has a chance to drink the antidote and reveal himself while dooming the other spies. [[spoiler:As it turns out, the ruler suspects that all the advisors are spies, they probably all are, the poison is actually in the stew, and the whole feast is just an example of what what happens to spies in the ruler's court.]]
** In ''Oblivion'', the sequel, there is actually a Dark Brotherhood mission where you are TheMole, tasked with killing a group of people alone in a house without them ever knowing who the killer is. Subverted a bit in that you can tell at least one character you are an assassin hired to kill her, and she likes you even more. The questline itself could be considered one, as later quests involve discovering who is the traitor to the Brotherhood ([[spoiler:It's Bellamont]]), and with the plot twist of The Mole framing others.
[[/folder]]

[[folder:Webcomics]]
* Webcomic example: In ''Jack'', the titular grim reaper takes the souls of 5 people killed in an explosion, and leaves it to them to find out who planted the bomb. It's never made clear precisely why he does this, although escorting souls to Judgement must get a little dull, so maybe this is how he entertains himself.
** He's apparently trying to help the "edge cases" save themselves, and maybe he feels he owes to Jatter, for he's part of the source of his crisis of faith.
[[/folder]]

[[folder:WebOriginal]]
* Used in ''{{KateModern}}'' during the "Trouble in Paris" arc, in which the situation is complicated by several characters having their own secrets, and by the fact that, with one exception [[spoiler:who ISN'T the mole]], the characters are all friends and protagonists.
*The story of the tail section survivors on ''{{Lost}}'': Nathan is the RedHerringMole. [[spoiler:Goodwin]] is TheMole. Then there's Cindy and Libby, and we ''still'' don't know what was up with either of them. Prevailing fan speculation is that Libby was TheMole, too, but for a different organization.
[[/folder]]

[[folder:WesternAnimation]]
* TransformersAnimated has this in the FlashBack filled episode "Autoboot Camp". [[spoiler: Wasp was framed, and the ''real'' mole went on to become the head of Autobot intelligence while Wasp slowly went insane. [[NiceJobBreakingItHero Way to go, Bumblebee]].]]
[[/folder]]

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