[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/eating_worms.jpg]]
[[caption-width-right:350:"Gagh?! Bah! Gagh is for pussies who can't handle a little crunchiness in their food!"]]

'''Original air date:''' May 9, 1988

The ''Enterprise'' is on its way to [[NamingYourColonyWorld Pacifica]], a [[SingleBiomePlanet water world]] for that much-needed R&R they mentioned last episode.

However, a priority call to Picard interrupts the mission, as it's Picard's old friend, Captain Walker Keel, on the line. He demands that the ship detour to an abandoned mining planet for a secret meeting. Picard is confused but curious, and humors him. Upon arriving at the planet and beaming down, Picard is confronted by not just Keel, but two other captains, who try to BluffTheImpostor to make sure Picard is really Picard before telling them of their concerns of a subversion in the Federation. The evidence is both vague and disturbing: mysterious disappearances and deaths in the ranks, bizarre orders and personnel shuffles, among other things. Picard doesn't buy it, but agrees to keep his eyes open for anything unusual that would corroborate their stories, assigning Data to look over Starfleet's recent activities upon returning to the ship as a precaution before heading back on course to Pacifica.

Unfortunately, the conspiracy decided to make its presence known shortly thereafter; the ''Enterprise'' comes across the destroyed wreckage of Keel's ship, and through his research, Data is able to confirm many of the odd occurrences Picard was told of, leading everyone to assume the worst: secret invasion. Picard decides to head to Starfleet Headquarters to figure out just what the hell is going on. Once there, Picard and Riker meet with a trio of admirals, all of whom seem to be acting very strangely. Things get weirder when we learn that one of them is Admiral Quinn, who, in a previous episode ("[[Recap/StarTrekTheNextGenerationS1E18ComingOfAge Coming of Age]]"), started the rumors of the conspiracy, but now insists he was only speaking metaphorically about [[TheAssimilator acquiring new members of the Federation]]. While Riker is still not convinced, Picard is, and orders him to keep an eye on this admiral while he goes on a tour of the ''Enterprise''.

Once on board, Quinn introduces Riker to a brain slug ([[Film/StarTrekIITheWrathOfKhan no, not those ones]]), batting him around like a rag doll when he refuses to become one with the thing. When Worf and Geordi fail to stop him, Quinn is eventually subdued by Dr. Crusher, and an investigation reveals a similar brain slug within him. Apparently, these are the things that are trying to subvert the Federation, and as Picard soon learns, they've made their way into the highest levels of Starfleet. Fortunately, Riker recovers enough from his beating to pull off a successful fake-out to rescue Picard from assimilation, and together, they face off against the mother alien, possessing Quinn's second-in-command, Commander Dexter Remmick, who defiantly insists they only wanted "peaceful coexistence." The episode ends on a RedHerringTwist, with a homing signal being sent out to the Delta Quadrant. TheEndOrIsIt

This episode was originally meant to be [[WhatCouldHaveBeen the prelude to the Borg]], but was ultimately left hanging as an {{cliffhanger}}, never to be followed up upon. Except, that is, in the Franchise/StarTrekExpandedUniverse, where the story got several contradictory resolutions. In the Literature/StarTrekNovelVerse the parasites are revealed to be mad, genetically engineered Trill symbionts that the Trill don't like to talk about, essentially the Trills' cultural equivalent to Romulans. In ''VideoGame/StarTrekOnline'', they're instead [[Recap/StarTrekTheNextGenerationS6E5Schisms Solanae]]-engineered infiltrators made for the [[Recap/StarTrekTheNextGenerationS2E11Contagion Iconians]] to infiltrate the [[Recap/StarTrekVoyagerS6E7DragonsTeeth Vaadwaur]].

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!! This episode contains examples of:
* AbortedArc: The series never followed up on the final cliffhanger in this episode--at least not straight: The Borg were originally going to be the follow-up to this episode and be an insect-like race, but that was too expensive.
* AmbiguousSituation: Remmick's recollection of Picard and their [[Recap/StarTrekTheNextGenerationS1E18ComingOfAge formerly antagonistic relationship]] is initially a HopeSpot: however badly the Admiralty has been infected, at least he's still on their side. Until it turns out that not only does Remmick have a parasite, he has ''the'' parasite. Since their AchillesHeel is their inability to access their hosts' memories, this raises one of three possibilities: that the queen parasite is for whatever reason not subject to this limitation; that she did a better job of doing her homework and knew of Remmick's history with the ''Enterprise'' through his logs; or, worst of all, that she had already infected him at the time of their last meeting.
* ArtisticLicenseBiology: The parasites have control of their host's adrenal glands, which gives them superior strength and durability. In reality, even a stiff shot of adrenaline isn't going to let an old man deliver high-kicks, beat up three fit young men, or resist a stunning effect that would instantly render a normal human unconscious.
* BatmanGambit: The controlled Starfleet officers reveal they knew about the secret meeting (as one of them was there). They orchestrated events so that Picard would head to Earth and be in a position to be overtaken.
* BestFriend: Picard considers Walker Keel and Jack Crusher to be his best friends, noting that they were "inseparable" when they attended Starfleet Academy together.
* BewareTheNiceOnes: Doctor Crusher just happens to have a phaser on hand to deal with Admiral Quinn, who has already taken down Riker, Geordi, and Worf.
* BigDamnHeroes:
** Dr. Crusher comes along just in time.
** It doesn't look like it at the time, but Riker appearing at the dinner.
* BlatantLies: "You don't understand. We mean you no harm. We seek peaceful co-existence!"
* BodyHorror: The mother-alien hiding underneath Remmick. And before that, we "get" to see [[YourHeadAsplode Remmick's head explode]]. This is ''not'' your average ''TNG'' episode.
* BrainsAndBrawn: How the possessed Scott describes the "relationship" between the slugs and those they possess.
-->"It's a perfect match. We're the brains, you're the brawn."
* BrainwashedAndCrazy: Everyone affected by the slugs.
* BrickJoke: Many times during the series, the organic beings express exasperation when Data is too precise or elaborates too much. It's quite something else when ''the Enterprise's computer'' does so while he is expressing wonder at talking to himself.
* CombatMedic: Doctor Crusher, with her prescription of a phaser set to kill. [[CombatPragmatist It proves much more effective than hand-to-hand combat.]]
* CurbStompBattle: When Quinn faces Worf, the showdown between them is given the weight of an act break, implying that they're about to have an epic battle. Instead, Worf puts up less of a fight than Riker and gets tossed over a table almost immediately.
* DarkerAndEdgier: This is an unusual ''TNG'' episode. Besides the graphic violence during the climax, the tone is consistently tense, the threat quite insidious, and Starfleet officers are basically shooting at each other.
* DeadpanSnarker: When Worf asks if he's all right, Geordi replies that if he could see, he'd be seeing stars.
* DynamicEntry: During the fight scene with Quinn vs Riker, [=LaForge=], and Worf, Quinn is blasted by a phaser by an unseen assailant on the other side of a doorway. One camera cut later, and a [[TranquilFury quietly furious-looking]] Doctor Crusher is standing in the corridor with a phaser.
* EarlyInstallmentWeirdness: Picard dispenses water from a small decanter set out in his quarters. No only is this odd because the decanter is the exact same size as his glass, but it's also made more clear in later episodes that the crew receive all their food and beverages outside of 10-Forward from the replicators. There's no reason for Picard to keep a glass of water stagnating at room temperature when he could instantly order a fresh glass at whatever temperature he specifies. This is before Picard's trademark demand to the replicator for "tea, Earl Grey, hot."
* TheEndOrIsIt: The final scene is Data reporting to Picard about the beacon and viewers hearing the signal.
* FakeDefector: Riker fakes being infected by the slugs so he can get into the conference room and help Picard. It fools ''everybody,'' [[HopeSpot Picard included]].
* {{Gorn}}: The death and destruction of Remmick and the mother parasite inside him was very controversial when it first aired. Creator/TheBBC cut several minutes of footage when first airing this episode in the UsefulNotes/UnitedKingdom, notably this part, and Canada's [[Creator/SpaceChannel Space]] network preceded the episode with a viewer discretion warning, the only episode of ''The Next Generation'' to receive one. The episode did win an Emmy Award for Outstanding Achievement in Makeup for a Series, though.
* HatesBaths: Worf's dislike of bathing extends to swimming of all sorts.
* HopeSpot: Picard has one when he's trying to escape from a room of possessed admirals and runs into Riker, only to discover that ''he'''s possessed, too. [[SubvertedTrope Subverted]], though, when Riker reveals that he was only ''acting'' possessed so he could get close enough to shoot the admirals.
* TheInfested: A man explodes, revealing himself to have been full of alien parasites.
* KeystoneArmy: The parasites are unable to survive after the mother parasite is destroyed.
* LiteralMinded: Data, as usual, regarding the experience of swimming in a real ocean vs. one on the holodeck.
-->'''Troi:''' Have you ever been for a real moonlight swim?\\
'''Data:''' One can swim in moonlight?
* MakeItLookLikeAnAccident: Shortly after Keel meets with Picard, his ship is found destroyed. When Picard asks, one of the mind-controlled Admirals says it was caused by "an implosion," and blames Keel's incompetence for the accident (after Picard has spent the whole episode talking up Captain Keel as one of Starfleet's best). In addition, several other officers have died off-screen in what were supposed to look like accidents.
* TheMainCharactersDoEverything: Riker calls for security while fighting with Quinn. Who responds? Worf and ''conn officer'' Geordi, but not a single security guard.
* MoreDeadlyThanTheMale: A CombatPragmatist (and non-lethal) version; Riker and Worf try taking on the parasite-possessed Quinn hand-to-hand, and experience total ass-whippings, while Geordi is knocked out before even realizing what's going on. Beverly then shows up and easily disables Quinn with her phaser, though it takes her a few shots.
* NiceJobFixingItVillain: The possessed Quinn initially came aboard the ''Enterprise'' in order to place Dr. Crusher under parasite control. However, he shows it off to Riker on the grounds that it likes him, which leads to the crew finding out what's really going on.
* ObviousStuntDouble: Not a lot of effort is made to conceal the fact that both Riker and Quinn are played by stunt doubles during most of their fight. It's much easier to spot in the modern, remastered edition than it probably was on a standard-def television in the 1980s, however.
* OnlyAFleshWound: Geordi is thrown ''through'' a closed door, landing in the corridor along with both halves of the door. He's on his feet again a minute later and reports back to the bridge after a quick visit to sickbay.
* OrphanedPunchline: After the opening [[CaptainsLog First Officer's Log]], we pick up the end of a humorous anecdote Geordi is telling to Data. Data responds by [[DontExplainTheJoke explaining the joke]] and giving a rather creepy laugh.
* TheParalyzer: Crusher stuns Quinn after multiple attempts. She later advises Picard to use the kill setting because the creatures are so resistant to stunning.
* ParasiticHorror: The parasites are played for various types of horror: firstly, they [[PuppeteerParasite change people's personalities]], secondly, they make people violent and [[SuperStrength super strong]], thirdly they themselves look pretty gross with their appendages sticking out of the person's neck, and fourthly, some of them breed in somebody's stomach, causing him to explode.
* ThePowerOfFriendship: Picard initially has his doubts about the conspiracy theory, but he implicitly trusts Keel--calling him a lifelong friend along with Jack Crusher.
-->'''Picard:''' Friendship must dare to risk, Counselor, or it isn't friendship.
* ThePowerOfTrust: Keel and the others warn Picard not to trust anyone, as there's no way to be sure a person is who they say they are. [[note]]This is demonstrated by Captain Scott being one of the conspirators all along.[[/note]] However, Picard trusts his crew unconditionally.
* PretendToBeBrainwashed: Riker shows up to dinner acting like he's been possessed by a parasite; he even has a phony gill on his neck that fools everyone else. (According to him, it was Beverly's idea.)
* ProperlyParanoid: Walker Keel is so certain of his belief that something is happening within the upper echelon of Starfleet Command that he's willing to breach official protocol to warn Picard, who initially brushes him off. Shortly afterwards, his ship implodes with him on board. This is enough to convince Picard that Keel was right all along.
* PunchCatch: Quinn does this successfully with Riker twice. First Riker throws a punch after Quinn painfully grabs his arm. Then as he picks himself off the ground, Riker throws another punch which Quinn catches and knocks aside, whereupon he viciously backhands Riker.
* PunchPunchPunchUhOh: Neither Worf nor Riker succeeds in causing any damage to the possessed Quinn.
* TheReveal: Captain Scott was under parasite control the entire time.
* RiddleForTheAges: The signal sent to a remote area of the galaxy by the parasitic aliens at the end is never brought up again in the series. Plans to pick the thread back up eventually got shifted into the Borg.
* RightHandVersusLeftHand: Data uses this analogy when describing the clandestine orders he discovered.
* RippedFromTheHeadlines: This episode was meant to be a commentary on the Iran/Contra scandal.
* RunningGag: Data is once again getting shushed by people for rambling on. This time, it's because he gives an excessive number of synonyms to explain himself. Riker first cuts him off, and then even the ship's computer does it.
* SciFiWritersHaveNoSenseOfScale: Early in the episode, Riker tells [=LaForge=] to increase speed to Warp 6, and he replies "Aye, sir. Full impulse." Errrr... the man said ''warp'', Geordi.
* SequelHook: A follow-up episode was planned, as the end seems to strongly suggest, but elements of it were instead folded into the Borg stories.
* ShoutOut:
** Someone in the scriptwriting team of the series seems to be a big fan of ''ComicBook/AlbedoErmaFelnaEDF'', a [[UsefulNotes/FurryFandom furry comic]], as two members of Starfleet (whose names appears in the Command Order) are named Itzak Arrat and Toki. In ''Albedo'', Arrat is also a spaceship captain and Toki is the main heroine's best friend (who happens to be female).
** Keel's ship is the USS ''[[Literature/HoratioHornblower Horatio]]''.
* SpottingTheThread: Picard's admiral buddy Quinn tells him and Riker that his mental fatigue was due to "[[TheAssimilator difficulty assimilating other races into the Federation]]". It's treated as a WhamLine, triggering "Something is dreadfully wrong" music and Picard telling Riker that Quinn is NotHimself. Note that this is ''before'' the Borg gave "assimilate" such an [[UnwillingRoboticisation ominous connotation]].
* {{Squick}}: Characters react with in-universe revulsion several times.
** The parasites gorge themselves on live mealworms. When Riker is expected to eat them, he can't help but look revolted and chooses this moment to break his charade.
** Commander Remmick's head explodes under continuous phaser fire, causing the mother alien to burst from his ribcage. Picard is so revulsed by the creature that he uncharacteristically starts blasting it.
* StockFootage: An establishing shot of Starfleet Command (a combination of miniatures, matte painting, and live action extras) is recycled from ''Film/StarTrekIVTheVoyageHome''.
* StoryBreakerPower: Invoked. It's why Picard has Data review six months worth of Starfleet directives. With his ability to go over information at such a fast rate, Data can see questionable patterns that anyone else would've missed. When he is done, he is absolutely certain there is a conspiracy at work.
* ThinkingOutLoud: Data discovers a new human idiosyncrasy.
--> '''Data:''' Startling. Quite extraordinary, in fact.\\
'''Computer:''' Directions unclear. Please repeat request.\\
'''Data:''' That was not a request. I was simply... talking to myself. A human idiosyncrasy, triggered by fascination with a particular set of facts. Or sometimes brought about by senility. Or used as a means of weighing information before reaching a conclusion. Or, as a--\\
'''Computer:''' [[YouTalkTooMuch Thank you, sir. I comprehend.]]
* TidallyLockedPlanet: Dytallix B was a world inhabited only by the Dytallix Mining Company. Due to the temperature extremes on either face of the planet, the company placed its facilities in the twilight region.
* TookALevelInBadass: Thanks to the aliens, an old man like Quinn has augmented strength.
* TrustPassword: Keel tests Picard about their shared history, as apparently those who are infected by the parasites can't access personal memories. Keel says that other officers he suspected were bluffing their way through talks of old times.
* ViolenceIsTheOnlyOption: While Picard always seeks to find a diplomatic solution first, he's moved by necessity and revulsion to simply kill the mother brain slug, which he laments in his final narration.
* WeirdWorldWeirdFood: The slug-controlled people eat live maggots.
* WhatHappenedToTheMouse:
** It's unclear if Captain Rixx survived or if Captain Scott killed him too, since she would've had just as much reason to have him killed as Keel.
** Other than Quinn, it's not made clear if the other people the parasites infected survived.
** We've never found out what happened with the signal Remmick sent.
* TheWorfEffect: The possessed Admiral Quinn easily hurls Worf over a table. Even Riker puts up a better fight than he does. And then moments later, ''Dr. Crusher'' effortlessly subdues Quinn, because she has the sense to just shoot him with a phaser instead of trying to have a fistfight with a superhuman.
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