[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/gelth_8934.jpg]]
->[[Recap/DoctorWhoS3E3TheMythMakers I saw the Fall of Troy!]] World War Five! I was pushing boxes at the Boston Tea Party! Now I'm gonna die in a dungeon.... in ''Cardiff!''
--> --'''The Doctor'''

The first episode MarkGatiss wrote for the TV series, based loosely on his AudioPlay/BigFinishDoctorWho episode [[Recap/BigFinishDoctorWho002Phantasmagoria "Phantasmagoria"]].

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The Doctor tries to take Rose to Naples, 1860. The TARDIS disagrees, and instead takes them to Cardiff, Christmas 1869.

Creator/CharlesDickens is in town, prompting an outbreak of earnest [[FanBoy fanboyishness]] from the usually sardonic Ninth Doctor. The squee doesn't last -- the dead are walking, so the Doctor springs into action. It turns out that there's a ''massive'' space/time rift right in the middle of Cardiff. This will [[Series/{{Torchwood}} become important later]]. A young psychic maid named Gwyneth ([[Recap/DoctorWhoNSS4E13JourneysEnd identical relative]] of one [[{{Characters/Torchwood}} Gwen Cooper]]) can guide things through the rift.

Dragging the very skeptical Dickens along, he organises a seance and negotiates with the aliens. If he helps them through the Cardiff Rift, they can temporarily occupy some corpses until he finds them a better home. Rose is {{Squick}}ed, but the Doctor [[CantArgueWithElves isn't in the mood to listen to some silly little human and coddle her delicate sensibilities.]]

The Gelth (as they call themselves) prove to be a bunch of lying promise-breakers, being "a few billion" in number and not being almost-dead. They were bent on wiping out humanity and taking over their corpses. The Doctor shows his raging SurvivorGuilt over having previously killed a few species, most recently his own, and hesitates to jump into action. Gwyneth takes the decision out of his hands by sacrificing herself. Charles Dickens learns an important lesson about Christmas, and merrily bids the Doctor farewell, planning to include all sorts of ghosts and blue lights and aliens in police boxes in his novels from now on. The Doctor gloomily notes that nothing will actually change, though, because Dickens will be dead of natural causes within a year.

The Cardiff rift remains open, and becomes a major feature of the {{Whoniverse}} from this point on.

!Tropes
* AliensInCardiff: TropeNamer, together with ''{{Torchwood}}'' (which this episode is a direct prequel to).
* ArcWords
-->'''Gwyneth''' (to Rose): The things you've seen. The darkness. The big bad wolf.
* BottleEpisode: The previous episode "[[DoctorWhoNSS1E2TheEndOfTheWorld The End of the World]]" spared no expense as it was to snag viewers after the has seen the premiere. This episode was filmed in the same block as "End of the World", and while there are special effects, note how this episode is a PeriodPiece to save money by using the BBC's already existing sets and costumes without having to create any.
* CantArgueWithElves: Or, in this case, with the Doctor.
* CastingGag: Simon Callow is a Dickensian scholar and has played Creator/CharlesDickens on several other programs.
** He later reprises the role in a cameo during Series 6, set in an alternate timeline where all history happens at once.
* ChangedMyJumper: TropeNamer. Nobody but Dickens remarks on the Doctor's attire anyway.
* ChristmasEpisode
* DevelopmentGag: The RunningGag about Cardiff apparently being a FateWorseThanDeath is probably an affectionate little jab, since they film in Cardiff.
* FalseInnocenceTrick: The Gelth claim to be refugees from the Great Time War who have lost their bodies and only want to use dead humans as Meat Suits. It turns out that there are many more of them than they claimed, and they want to take over all humanity, not just the dead ones.
** Granted, they're not actually lying--the key here is that they just need dead bodies. A few billion. Which means a majority (if not all) of the human population of Earth at the time.
* {{Foreshadowing}}: The Doctor and Dickens talking about ''The Signal-man'' and ''A Christmas Carol''.
* GhostlyChill: The morgue cools down when the Gelth appear.
* TheGreatestStoryNeverTold: Rose laments that no one will ever know what Gwyneth did.
* HeroicSacrifice: By Gwyneth to sabotage the Gelth.
* HistoricalDomainCharacter: Creator/CharlesDickens
* HistoricalInJoke: Dickens declares his intention to incorporate the Gelth into the climax of ''The Mystery of Edwin Drood'', a novel that famously went uncompleted due to AuthorExistenceFailure.
* IWasJustPassingThrough: The Doctor claims this when Dickens inquires as to his true identity.
* TheKnightsWhoSaySquee: The Doctor squees at learning he's sitting next to ''Charles Dickens''.
* LamePunReaction
--> '''Doctor:''' Don't antagonise her. I love a happy medium.
--> '''Rose:''' I can't believe you just said that.
* NewspaperDating
* OminousFog
* PsychicPowers: Gwyneth.
* PuppeteerParasite: The Gelth.
* RebelRelaxation: The Doctor, while watching Dickens check out a corpse.
* SpookySeance
* TemporalParadox: Rose ''thinks'' that this means the Gelth can't kill her in 1869, since she's still living in 2005. As the Doctor explains, however, time travel doesn't work that way -- her travel from 2005 to 1869 doesn't affect her ability to die.
* VictorianBritain: Cardiff, 1869.
* WhiteMansBurden: Subverted. In a temporal socio-economic version of the trope, Rose takes pity on Gwenyth and tries to stop the Doctor from 'using' her to et the Geth through. Gwenyth does not appreciate this, accusing Rose of thinking that she's stupid and unable to understand what is going on just because she didn't have an education.