[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/babel_virus.jpg]]
[[caption-width-right:350:"I'm sorry, Chief, what's this about hovercrafts and eels again?"]]

O'Brien has been run ragged all across [=DS9=], fixing one broken system after another. While fiddling with the main floor replicators, his day gets worse. He is infected with an aphasia virus, a disease that leaves him babbling incomprehensible gibberish. It was left in a booby trap planted by Bajoran terrorists during the early construction of [=DS9=].

To make matters worse, the virus is spreading thanks to Quark, who has been secretly using an infected replicator to take up the slack of his own malfunctioning replicator. With O'Brien suffering a heavy fever, it's become apparent this virus is fatal.

Doing a little digging, Kira traces the disease back to its creator, a Bajoran terrorist named Dekon Elig. Unfortunately, he's dead, having been killed trying to escape Cardassian confinement. With that lead a dead-end, Kira seeks out Surmak Ren, the doctor who signed Dekon's death certificate. At the first mention of the virus, he terminates connection.

Almost all of [=DS9=] is infected, with only Sisko, Odo, and Quark unaffected. Kira leaves to "persuade" doctor Surmak to assist her, while Sisko and Odo deal with another problem: A panicking cargo captain named Jaheel attempts to leave the station. Sisko insists he can't risk spreading the virus, but Jaheel persist and fries his ship trying to tear loose from the docking ring with the clamps still locked. Now his ship is a ticking time bomb, about to take the docking ring with it.

Meanwhile, Kira has located Surmak. Beaming him straight from his office to a Runabout, Kira reveals to the good doctor that she was already infected, and so now he is infected as well. This more than convinces him to get working an an antidote.

Sisko finally gives in to the virus, leaving Odo alone at Ops. Enter Quark, who uses his experience working on a Ferengi freighter to man the transporter for Odo so he can rescue Jaheel and jettison his ship before it explodes.

With that, the virus is cured and life aboard [=DS9=] returns to normal -- and O'Brien goes back to being overworked.
----
!!Tropes:

* AdmiringTheAbomination: Bashir calls the virus a work of genius.
* BadToTheLastDrop: The plot kicks off because the replicators can't produce [[MustHaveCaffeine a decent cup of coffee]], and it's O'Brien's repairs that sets off the booby trap. At the end of the episode, with the device removed, the replicators ''still'' won't put out good coffee, forcing Miles to have to fix them again.
* BaitAndSwitch: Quark is in the emergency sickbay apparently affected by the virus, but he's actually trying to talk a sick customer into paying their bar bill.
-->'''Quark:''' Food, dabo, drinks, money, hand mine...Give!\\
'''Sisko:''' Well, Quark, I see even you couldn't weasel your way clear of this one.\\
'''Quark:''' You underestimate the Ferengi immune system, Commander. I'm merely here visiting my less fortunate customers to make sure they're not faking the illness to avoid paying their bills.\\
'''Sisko:''' No one's that devious.\\
'''Quark:''' I am.
* BlatantLies: After illegally hacking the replicators on the command deck, Quark tries claiming Rom fixed the bar's replicator. Odo doesn't buy it because "Rom is an idiot."
* ButtMonkey: Starting his long tradition of being [=DS9=]'s punching bag, O'Brien is the first infected with the virus after being worked to the bone repairing malfunctioning system after malfunctioning system. He also comes closest to dying of the virus.
* ClosestThingWeGot:
** With most of the Starfleet and Bajoran personnel incapacitated by the virus, Sisko recruits Odo to fill in, despite his protestations that he's trained for security, not station operations. Odo is, in turn, forced to rely on ''[[SitcomArchNemesis Quark]]'' when he is the only one able to come to Ops and help Odo get Jaheel's ship free of the station before it explodes.
** Surmak protests that he was just a medical assistant to the Underground scientist who created the virus. But as that makes him the only person alive who knows anything at all about it, Kira kidnaps him. Fortunately he's able to use the work Dr. Bashir has already done to work out a cure.
* CorruptedContingency: The device that reprograms the replicator to produce the virus was originally planted by the Bajoran Resistance as a BoobyTrap against the Cardassians, and not removed when they withdrew from Bajor mainly because its creator had later been arrested and then killed in a failed prison break. It is triggered accidentally when the malfunctioning replicator is repaired.
* CurseOfBabel: The bioweapon causes aphasia, a real-world condition where the neural connections between words and the concepts they represent become scrambled, causing victims to speak the wrong words. In real life it sometimes happens in stroke or head injury victims.
* DeadpanSnarker:
--> '''Jaheel:''' Dog! Fellow! Distance!\\
'''Odo:''' Tell me about it.
* DwindlingParty: A non-fatal example. One by one people on [=DS9=] are affected by the virus and rendered unable to help, with Sisko and Kira holding out the longest until only Odo and Quark (and the only recently infected Surmak) remain to save the day.
* EarlyInstallmentWeirdness:
** Quark quotes an "old Ferengi saying" instead of a Rule of Acquisition.
** Odo figures out that Quark was lying because Quark claimed that Rom fixed a replicator, and Odo states, "Rom is an idiot." Rom would later be characterized as an idiot savant with technology.
** Early episodes of the show seemed not to have nailed down how the symbiont worked yet (almost certainly compounded by the fact that the TNG incarnation of the Trills were very much of the PuppeteerParasite type). Jadzia's comment that she has forgotten what it was like to be a woman after eighty years of being a man implies that the symbiont is talking ''through'' her rather than it just being a reservoir of memories and emotions as was established later on.
* EverybodyLives: This is the first major station-wide crisis episode of the show, with a potentially deadly disease running rampant throughout [=DS9=], as well as a terrified freighter captain risking destroying his ship and half the docking ring in his desperation to escape. Despite this, the situation is resolved with no reported casualties; the virus is cured before it can kill anyone, while the freighter is exploded harmlessly in space, Odo having rescued the captain before it was ejected.
* {{Foreshadowing}}: Bashir makes an offhand comment about having studied genetic engineering.
* FromBadToWorse: Bashir reports that the virus has become airborne, meaning that nobody on [=DS9=] is safe. Then O'Brien develops more serious, life-threatening symptoms, showing that the virus is much more serious than it initially seemed.
* GotVolunteered: Played straight with Surmak, and averted with Quark who insists on being paid if he's going to help out Odo in Ops.
* HeadTurningBeauty: Jadzia is strolling the promenade with Kira and enjoying the greetings of passing men, saying she's forgotten how different being a woman was.
* HereWeGoAgain: After all the trouble they went through, [[LastSecondJokeProblem the replicators in Ops are still broken and Sisko barks at O'Brien to fix it]].
* IdealIllnessImmunity: Odo and the various Ferengi on-board end up being the only ones immune to the virus, Odo because he lacks a humanoid structure for the virus to attach to, and the Ferengi because their immune systems are just that damn good.
* IResembleThatRemark: When Sisko says that no-one would be devious enough to fake being sick just to avoid paying their bar tab, Quark casually replies, "I am."
* IronicEcho: Sisko admits that Odo is probably right about being unqualified for station operations, but it's necessary anyway because [[ClosestThingWeGot "you're all I've got"]]. When Kira presents her plan to kidnap Surmak Ren, Odo suggests that Sisko go along with the idea because "she's all you've got".
* KarmaHoudini: Kira kidnaps Surmak Ren and deliberately exposes him to a deadly virus. She says she’s willing to go to prison for what she’s done, but in the end there are zero consequences for her actions.
* LockDown: Sisko locks down the station the moment he realises a virus is responsible. Captain Jaheel isn't happy and tries to break free of the docking clamps, at the risk of destroying his ship and the station for a CommercialBreakCliffhanger.
* LoopholeAbuse: Sisko doesn't want Kira going to look for Surmak out of fear she will spread the virus. Kira promises that she won't leave her runabout, and gets around the risk of spreading the virus by kidnapping Surmak via transporter.
* MilkingTheGiantCow: Quark trying to communicate with the aphasia victims.
-->'''Quark:''' You, gold owe MEEEEE!
* NeverGiveTheCaptainAStraightAnswer: Bashir summons Sisko to the Infirmary with the usual "I think you'd better get down here as soon as possible" line. When Sisko gets there, he sees that Jake is infected.
* NotMeThisTime: Kira blames the sabotage on a Cardassian plot, but ironically it's her former comrades in the [[LaResistance Bajoran underground]] who were responsible. The BoobyTrap was set up when the station was first built eighteen years ago, but never triggered because the terrorist cell was rounded up before they could put their plan into action.
* NoSocialSkills: Quark is getting bored in his empty bar and invites Odo to join him in a game of dabo. Odo curtly refuses, then reluctantly admits that he never learned how to play.
* NotSoStoic: When Sisko goes down, Odo is on the verge of panic handling the unfamiliar duties of station ops, as Quark gleefully notes.
* PlotDemandedManualMode: Odo has to release the docking clamps manually after Captain Jaheel damages them trying to break his ship free.
* ShoutOut: To ''WesternAnimation/TheRenAndStimpyShow''.
** Surmak Ren is the most obvious one, supported by the fact that Ren is the son of Hoek (Ren's last name) and Stimson (Stimpy's real name).
** Gul Spumco is named after the production company that produced the animation.
* ShownTheirWork: In real life, aphasia affects a person's ability to understand both written and spoken language, not just their ability to speak coherently. Not only are the affected clearly unable to understand the unaffected, but a moment after Bashir starts addressing the sickbay computer in gibberish, a WhamShot shows the screen from his perspective - a jumble of random words.
* SomeoneElsesProblem: Surmak never told anyone about the BoobyTrap the Underground left on the station eighteen years ago, and refuses to help until Kira forces the issue by [[GotVolunteered exposing him to the virus as well]].
* TakingYouWithMe: Kira convinces Surmak to work on curing the virus by abducting him and revealing that he is now infected.
* TalkingWithSigns: Attempted with a padd, but the written words turn out to be gibberish as well.
* TamperingWithFoodAndDrink: The sabotage device modifies the replicator so it will create the bioweapon in the food and drink it produces.
* TemptingFate:
** O'Brien fixes the ear-splitting whine from Dax's replicator.
--->'''O'Brien:''' That should do it! ''(Cue BigBlackout)'' [[SarcasmMode Anything else I can do for you?]]
** O'Brien just wants five minutes peace. Sisko then complains about him not fixing the replicators.
** O'Brien gets the replicators working perfectly, only to end up triggering a BoobyTrap that distributes a bioweapon into them.
* TranslationByVolume: Quark tries this on several patients who owe him money. Obviously, it doesn't help.
* {{Troll}}: Quark offers to beam Odo to Jaheel's ship, citing his service aboard a Ferengi freighter. He then says "I must have ''witnessed'' the procedure a hundred times," right before energizing.
* UnwittingInstigatorOfDoom: Thanks to Quark secretly using the working replicators on the command deck to supply his bar, the virus spreads that much more quickly through the station.
* WhatHappenedToTheMouse: Quark is seemingly immune to the virus due to his Ferengi biology, and yet Rom, Nog, and the other Ferengi aboard the station are nowhere to be seen even after Sisko sent out a request for every able-bodied person to come to ops.
* WordSalad: How everyone infected with the virus talks.