'''Season 2, Episode 17''':
!Proteus

The Machine gives Finch and Reese the numbers of six individuals who have all vanished without a trace from various cities throughout the country, and who may have all been victims of a serial killer who likes to take over the lives of the people he kills. Their investigation leads them to Owen Island, where they are forced to [[BigStormEpisode wait out a severe storm]] with a group of locals and unknowns... one of whom may be the killer they're searching for.

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!!Tropes present in this episode include:
* BigDamnHeroes: Carter and Cal play this at the end.
* BlindWithoutThem: Finch can't tell for a moment who saved him, as the killer removed his glasses. Or at least that's what he wants Carter to think; given that the killer wore his glasses without squinting and he didn't seem to have any trouble seeing until she showed up, there's a decent chance he's faking.
* BrickJoke: Reese knocks out the fisherman, drags him off for disposal while grumbling about his lot, then gets hit on the head. Then the whole process repeats, with Reese and the fisherman in swapped roles.
* BulletProofVest: Saves the murderers life the first time he's shot. [[BoomHeadshot The second time... not so much.]]
* CantKillYouStillNeedYou: The killer needs Finch to fly him off the island first. But when Finch gives his TheReasonYouSuckSpeech, he decides to kill him then and there.
* ClosedCircle
* ConvenientlyTimedAttackFromBehind: As noted by Finch when Carter saves his life. Moments later, Carter and Finch have their lives saved by Cal.
* ConvictionByCounterfactualClue: Reese says the K-Bar the deputy was stabbed with isn't something you can get in a bait and tackle store, as it's a Marine Corps knife. He might have mentioned that any military surplus store would have one, not to mention they're readily available online. It does however scare the man into admitting he's a Marine deserter and the knife is his, but he denies using it to murder anyone.
* DangerousDeserter: Apparently the first suspect, but averted.
* DetectiveMole: The SerialKiller killed the FBI agent tracking him down and took his place.
* DisposingOfABody: Finch (with the help of Bear) finds the charred teeth of a previous victim in a furnace. The killer later complains of the difficulty of disposing of the teeth.
* DramaticThunder: A more subtle version.
* DrivesLikeCrazy: Cal loses his temper when Carter suggests he might be a DirtyCop, and puts his foot down while driving through a storm. When he realises what's happening and stops, Carter has her hand on her gun.
* EveryoneIsASuspect: Well considering they have no idea who they're looking for, yeah.
* ExplainExplainOhCrap
-->'''Finch:''' He was posing as an FBI agent. He was really quite good at it; he had a badge and a gun and... [[NotQuiteDead body armor...]]
* {{Foreshadowing}}: Finch and Reese both know something is wrong with The Machine because it went three days without giving them a new number. There were also a large number of blue-screens visible during the shots where the Machine pans from one scene to the next.
** At the start of the episode, Finch and Reese come out of a theatre showing ''Film/{{Rashomon}}'' and ''Rain People''.
* FourEyesZeroSoul
* FrameUp: The marine deserter's knife is used to kill the deputy.
* HiddenDepths: Finch can fly a plane. Also doubles as an OffscreenMomentOfAwesome because he quite successfully landed his seaplane in the middle of the town.
* HostileWeather: The storm that traps them on the island with the SerialKiller.
* INeedAFreakingDrink: Finch doesn't turn down a QuickNip when it's offered. After the crisis is over, Cal shares a drink with Carter, noting that any police station has a bottle of booze somewhere.
* IfIDoNotReturn: Reese tells the FBI guy to get the others to safety if he doesn't come back from chasing the fisherman.
* KillAndReplace: Not only the killer's M.O., but something he's compelled to do. When he says he'll stop doing it when he finds the perfect identity that fits him, Finch knows he never will.
* TheKillerWasLeftHanded: Cal spots the person on a video tape isn't the same man who came back the next day because he used his left hand to unlock the door.
* LieDetector: Finch rigs up an improvised version with seimograph equipment, measuring the micro-tremors from the interviewees hands resting on the table.
* LightningReveal: Well that was freaky.
** Note: You can see the guy behind Finch near the start of the scene, nearly invisible in the darkness -- it's just that if you're not looking for him, the lightning is the first time you know he's there.
* LightsOffSomebodyDies: The power goes out just as Carter is getting through on the radio. Reese goes to reconnect the generator, only to find the radio trashed and the deputy murdered.
* NoodleIncident: Reese noted that this was not the first time someone shot at him with a spear gun.
* NotSoDifferentRemark: The murderer points out that he and Finch are a lot alike in their approach to assuming a false identity and hiding who they really are.
* OhCrap: When Finch realized that the Killer had a BulletProofVest. And earlier when Finch studies the lie detector printouts and realises he'd ignored the reactions of the FBI agent.
* OOCIsSeriousBusiness: The Machine is visibly slowing down, and Finch worries that whatever virus Stanton uploaded may be the cause.
* OohMeAccentsSlipping: In-Universe example. The serial killer's accent is all over the place during his climatic scene with Finch, including a truly chilling moment when he reveals that he plans to assume Harold's identity and then he repeats Finch's previous question [[BrokenRecord multiple times]] so that he can [[NightmareFuel adopt his speech pattern]].
* PunkInTheTrunk: Reese is about to do his usual thing with the fisherman, only to find someone already in the trunk, the FBI agent he's supposedly working with.
* TheRadioDiesFirst / CellPhonesAreUseless: The bad weather first interferes with Reese and Finch's cell phone connection, and then later the murderer destroys the radio at the police station after Carter tries to contact them with information about his identity.
* ReasonableAuthorityFigure: The local sheriff is pretty accommodating to Reese and the FBI agent, while providing some theories of her own.
* RedHerring: Several. The killer disposes of the people he replaces by burning their bodies after pulling out their teeth, two of the suspects are dental hygienists. One man owns a military grade knife that is used in a killing. A third is a fisherman who keeps trying to get to his boat in the middle of a storm. A fourth is a developer checking on his project who the townspeople explicitly note that they haven't met in person yet. The dental hygienists are just dental hygienists. The man with the knife is a deserter from the Marine Corps. The fisherman is a drug smuggler. The developer is the real developer. None of them are the killer.
** StealthPun: the fisherman is a RedHerring.
* SerialKiller: The bad guy of the week.
* ShutUpHannibal: Finch delivers a nice one while talking with the murderer.
* ShoutOut: Harold Finch was totally channeling [[{{Series/Lost}} Benjamin Linus]] during his confrontation with the murderer.
-->''"You'll never get off the island."''
* SpoilerOpening: [[RewatchBonus You probably won't notice it on the first time]], but usual CouchGag shows two different scenes - one with today's number, other with Reese entering the garage. This is his scene with today's killer, but we don't know it yet.
* AStormIsComing : At the end of the episode they have this conversation.
-->'''Reese''': At least the storm is passing.
-->'''Finch''': No, Mr. Reese, I have a feeling that [[ItHasOnlyJustBegun it's just beginning]].
* ThatsWhatIWouldDo: Finch notes that the killer would erase his previous identity after he'd finished using it, because that's what he does.
* UmbrellaOfTogetherness: [[HoYay Finch and Reese]] going out of the cinema.
* WholePlotReference[=/=]ShoutOut: ''Literature/AndThenThereWereNone'' -- the name of the island, Owen Island to the character that invited the guests in the Agatha Christie story, UN Owen(Unknown). The nature of the storm causing everyone to be trapped is also similar. It also takes the idea of a serial killer taking over victims' identities from ''Film/TakingLives''.