The Sixth Doctor takes Peri to a lexicographer's convention, where his old friend Professor Osefa is about to unveil the Lexicon, the most comprehensive dictionary of the English language ever written. The Doctor is immediately welcomed as an honored guest, while Peri sneaks off to go get drunk about two seconds in.

While Peri hits it off with a charming young logophile named Warren, the Doctor discovers something far less pleasant -- Osefa has seemingly committed suicide in a locked room, but a suicide note riddled with misspellings and errors raises the Doctor's suspicions. Since calling the police would be pointless ([[HandWave jurisdiction troubles, you see]]), the Doctor and Symposiarch Bob Cawdrey decide to investigate.

The last person who talked to Osefa was the Book, a sentient computer program designed to collect and index ''all'' English words ever written or spoken. Warren, however, is convinced that Book is miserable in its neverending task, and destined for greater things. In fact, Warren is against a lot of things -- he takes exception to Cawdrey as well, and curiously enough, he has something against dictionaries.

The Doctor uses Osefa's BizarreAlienBiology to create a makeshift VirtualGhost out of her memories. It turns out that Osefa and Book recently visited an ancient tribal culture, whose people believed that all of language was created by a single word. Osefa turns out to have used grant money to investigate a very non-scientific field called transcendental linguistics (which greatly offends Cawdrey). She was convinced that the amount of possible meanings a word can have reflects its lexical status. For example, a word like "as" or "so" can have dozens of meanings, whereas longer words are less frequently used, therefore more rare, therefore the longest word in the universe -- the Omniverbum -- will only have a single meaning and thus have maximum lexicographical weight. Everyone's all very skeptical about this until the conference's guests get stuck on a MadnessMantra of "...ish". And all the written text around them spontaneously develops errors.

The Doctor gives Peri and Cawdrey devices that bleep out the MindVirus when it's spoken by them, and discovers that the ''...ish'' is a sentient affix of the so-called Omniverbum. Warren, meanwhile, turns out to be a sentient computer program much like Book, but isn't aware of it. All he knows is that his job is to index things where even Book couldn't reach: the words of the rival lexicographers themselves. It turns out that Cawdrey created him and linked him to Book in order to sabotage rival lexicography projects. But Warren rebelled, believing that the indexing of language destroys spelling variations and, thus, creativity. He plans to instead erase language as a whole, allowing for a completely free flow of thought and creativity without set meanings, and bring the Omniverbum into this world properly... starting with the ''...ish.''

While Osefa's virtual ghost stages a distraction, the Doctor, Peri and Book end up defeating Warren by very literally TalkingTheMonsterToDeath. The ''...ish'' just wants to go home in the end, and Osefa's copy and Book decide to work together on decidedly more traditional linguistics from now on.

!!...ish contains examples of:
* AddedAlliterativeAppeal: The Doctor throws a few in there in this adventure.
* AIIsACrapshoot
* AndIMustScream: [[spoiler: Cawdrey, a linguist, is left "without language... forever" by the end of the story. Given all the various things that the Doctor described as "language" earlier in the audio, this can be ''very harsh indeed''.]]
* AndThenWhat
* ApologisesALot: Cawdrey.
* ArtificialIntelligence: Book [[spoiler:and Warren.]]
* ArsonMurderAndJaywalking:
--> "Pages of text books are spilling out on the floor! Covered in nonsense verse! The translation systems are speaking in tongues! And the attendee listings for the conference, which I've personally checked three times has... has...! ''[[WhatDoYouMeanItsNotHeinous TYPOS]]''!"
* AscendedMeme: In-universe. "A fully sentient meme, and all you care about is 'me'!"
* BattleInTheCentreOfTheMind
* BrownNote: The ''...ish'' causes anyone who hears it to become mentally "stuck" on it and repeat it over and over.
* CensoredForComedy: At one point the Doctor equips himself, Peri and Cawdrey with linguistic devices that bleep out ***.
* ContemplateOurNavels
* ContinuityNod: When the Doctor and Peri trade English and American terms to confuse the Ish, they pair off different pronunciations of lieutenant (“loo-tenant” versus “lef-tenant”), referring to a similar joke in "The Twin Dilemma". Peri also mentions her abusive stepfather again, gets a nice ScienceHero moment with her knowledge of botany terms, and briefly ponders whether or not she's technically still a student. Oh, and the Doctor [[Recap/DoctorWhoS7E1SpearheadFromSpace speaks a bit of Delphon]].
* CreationMyth: The natives of Xenocubis believe that the echoes of the Big Bang created the "first great Word," which gave rise to language. All languages are thus a corruption or fragment of the original Word.
* CreepyMonotone: [[spoiler: When the guests start saying "ish" at the end of episode two. Except the Sixth Doctor, as per usual, who seems to be in a [[NoIndoorVoice shouting match]] with one of the guests.]]
* DepartmentOfRedundancyDepartment: Cawdrey apologizes. ''A Lot''.
* EldritchAbomination: The ''...ish'' is a living, sentient word which literally eats meaning and can reduce humans to babbling zombies just by being spoken in their vicinity. [[spoiler:In the end, though, it just wants to go home, which makes it one of the milder examples of this trope.]]
* EternalEnglish: Played straight.
* FascinatingEyebrow: The Doctor claims the language of Delphon is done entirely by raising one's eyebrows. And that [[{{Omniglot}} he speaks it]].
* FinishingEachOthersSentences: Warren and Peri hit it off so quickly that they do this.
* FunnyBackgroundEvent: [[spoiler: When the Ish makes its presence known at the end of episode 2, The Doctor can be heard in the background emphatically arguing with someone while only saying "ish".]]
* GettingCrapPastTheRadar: At one point during CensoredForComedy Peri utters "We're ***ed."
* GrammarNazi: The Doctor describes tenses and variants in gusto of how the English language SHOULD be spoken.
* GreatBigBookOfEverything: Book is trying to become one.
* InherentlyFunnyWords: Sausage.
* MythologyGag: There are some amusing in-jokes amidst the wordplay in ...ish. One of Warren’s acts of sabotage apparently resulted in the creation of an impossibly thick encyclopedia volume starting with DAL, referring to Terry Nation’s apocryphal claim to have named his creations from the spine of an encyclopedia volume covering DAL to LEK. The Adjective of Noun is used to describe the structure of many classic episode titles (especially those of Season 14).
* InsufferableGenius: The Doctor LOVES being described as the master of English.
* ItsPronouncedTroPAY
* LongList: The diction, different spellings, capitalizations, alternate alphabetical arrangements, synonyms, homonyms, hyphenations, etc. etc. etc. etc. that Book knows. Even describing what the LongList entails is an [[OverlyLongGag Overly Long List]].
* MindVirus
* OrphanedPunchline: [[InherentlyFunnyWords Sausage]]. Again.
* SayMyName
* SeparatedByACommonLanguage: The Doctor and Peri argue over Americanisms, which the Doctor considers a corruption of the English language. [[spoiler:[[ChekhovsGun Later,]] they use equivalent terms in American and British English to confuse the ''...ish'' and send it into retreat.]]
* SesquipedalianLoquaciousness: Inevitable in a story about word-lovers. Six takes particular pleasure in showing off his vocabulary.
* ShouldntWeBeInSchoolRightNow: Peri isn't ''entirely'' sure whether or not she's still a student.
* ShoutOut: The AAH-AAH!! sound effect from ''Series/FamilyFeud'' gets used.
** The "Beginning" of the Dictionary being Aardvark could very well be one to Series/BlackAdder the third.
** "[[Film/{{Alien}} Even in space, you could hear it scream]]."
** "[[Literature/MobyDick Call me Ishmael...!]]"
* SoundEffectBleep: Used in-story as a means to keep Peri and Bob from hearing or saying ''...ish''.
* SpiritualSequel: To [[Recap/BigFinishDoctorWho003WhispersOfTerror "Whispers Of Terror"]].
* TalkingTheMonsterToDeath: Perhaps the most literal use of the trope ever.
* TomatoInTheMirror: [[spoiler:Warren]].
* VerbThis: The Doctor himself. "Oh, circumlocute ''this!''", to [[spoiler: Warren.]]
* VirtualGhost: The Doctor brings Osefa back as one of these to investigate her alleged suicide. In a rare variation of the trope, [[spoiler: she continues to live, without drama.]]
* TheVirus: ...Ish.