[[caption-width-right:350:Get ready, boys and girls; the Doctor's about to monologue!]]

->''Homo sapiens. What an inventive, invincible species. It's only a few million years since they crawled up out of the mud and learned to walk. Puny, defenceless bipeds. They've survived flood, famine and plague. They've survived cosmic wars and holocausts. And now, here they are, out among the stars, waiting to begin a new life. Ready to outsit eternity. They're indomitable. Indomitable.''
-->-- '''The Doctor'''

The one with killer bubble wrap.

Before ''Film/{{Alien}}'', there was "The Ark in Space". [[note]]Wait, we've [[BrickJoke made]] [[Recap/DoctorWhoS9E1DayOfTheDaleks this joke]] [[LampshadeHanging before...]][[/note]]

The TARDIS arrives on an apparently deserted space station in Earth orbit, some time in the far future. Investigating, the Doctor, Sarah and Harry discover that the remnants of the human race are in suspended animation awaiting Earth's return to habitability following solar flares. The Doctor realises that the Earth is in fact now habitable again and activates the controls to begin reviving the humans. However, there appears to be something amiss -- some controls are damaged (which is why the alarm clock didn't go off) and there are green trails around the place.

It seems that a race of giant insects -- the Wirrn -- are also aboard. Eggs have been laid in the solar stacks, and larvae are glimpsed. One of them infects the human leader, Noah, who begins turning into a Wirrn himself. The Doctor and his companions gain the trust of the other defrosted humans, now led by medical officer Vira, and together they lure the hatched Wirrn onto a shuttle craft and launch it into space. Noah, using the last vestiges of his humanity, deliberately doesn't set the shuttle's stabilisers and it explodes.

Both Creator/RussellTDavies and Creator/StevenMoffat have cited this as their favourite serial from the original run of ''Doctor Who''.
* AirVentPassageway: Unlike what's usual for this trope, Sarah Jane is the only one thin enough to get through the vent, and even she gets stuck.
* AlmostOutOfOxygen: One of the first things the Doctor needs to fix on the Ark is the oxygen supply. Later on, the Wirrn deliberately cut off the air, because they can survive for longer periods without breathing, but the humans obviously can't.
* ApocalypseHow: Solar flares toasted the Earth, likely afflicting Total Extinction on anything that hadn't evacuated.
* TheArk: The Earth is rendered temporarily uninhabitable by solar flares, and the surviving humans, as well as samples of the animal and plant life, sit it out in suspended animation on a space station. (The station commander even adopts the name "Noah"; Vira tells the Doctor that they know it's not much of a joke, but under the circumstances they were taking their laughs where they could find them.)
* BigCreepyCrawlies: The Wirrn.
* BodyHorror: Noah's transformation.
* BottleEpisode: The first episode features just the Doctor, Sarah, Harry and no other characters save for some cryogenically frozen extras. This was because the set had been extremely expensive to construct. The set [[RecycledSet reappears]], with some light modifications, later on in [[Recap/DoctorWhoS12E5RevengeOfTheCybermen "Revenge of the Cybermen"]].
* ButtMonkey: Harry Sullivan. Almost everything the Doctor says to him in this episode, even when he's complimenting him on figuring something out for himself, amounts to "See, Harry? You're not a ''total'' fucking idiot, are you?"
-->'''Doctor:''' You're improving, Harry! Your mind is beginning to work. It's entirely due to my influence, of course, you mustn't take any credit.
* ChekhovsGun: While working on the shuttle craft, the Doctor removes a piece of metal and puts it in his pocket. It's still there in the next story and saves his life when [[PocketProtector the bad guy shoots him]].
* ChromosomeCasting: Apart from Sarah, Vira is the only female character in the story.
* CryonicsFailure: Because the Wirrn sabotaged it, the waking system doesn't work. And Dune is eaten by Wirrn larvae while suspended.
* DeadpanSnarker: Rogin.
* DecontaminationChamber
* EarthThatWas: A marginal case, since the whole point of the Ark was to enable humans to repopulate the Earth when it was safe to do so. So really it's the Earth That Was And Will Be Again.
* EmotionlessGirl: Vira never shows much emotion, at least until the moment she realises the mission has succeeded..
* FightingFromTheInside: Noah manages to get a message back to Vira while the Wirrn is converting him. And at the end, he is strong enough to not save the Wirrn despite knowing how.
* FlingALightIntoTheFuture: The purpose of the Ark is to make the human race survive.
* HeroicSacrifice: Both Rogin and Noah.
* HighVoltageDeath: The Wirrn's main weakness.
* HomeworldEvacuation: Humankind have evacuated the Earth in order to being a new life when the planet is devastated by solar flares.
* HumanPopsicle: Humanity froze itself to wait out an environmental catastrophe. Ironically, the Doctor himself makes the cryogenic/cryonic mistake, while belittling poor Harry's intelligence.
* HumansAreTheRealMonsters: In spite of the Doctor's obvious faith in humanity, there is evidence that they are not so virtuous after all. The Wirrn's plan to destroy humanity and steal their knowledge is an act of revenge for the destruction of their original breeding colonies in Andromeda by the human empire. When Vira learns of this, she is delighted that the occupation of Andromeda was successful, instead of sad that it caused large scale misery for another species.
* HumansAreSpecial: See the page quote.
--->"It may be irrational of me, but humans are quite my favorite species."
* IKnowYoureInThereSomewhereFight: The Doctor appeals to what is left of Noah's humanity by reminding him of the beauty of Earth. Noah claims to have no memories of it, but considering how he stops the Wirrn at the end, it seems the Doctor got through to him.
* InspirationalInsult: The Doctor intentionally insults Sarah Jane and hurts her feelings in order to help her achieve the AirVentPassageway escape. Needless to say, he doesn't mean it.
* LawfulStupid: Every human in this time, apparently. Noah is the worst.
* LightningGun: The automatic defense system has one.
* MinimalistCast: The Doctor, Sarah Jane and Harry are the only characters on-screen in the first episode.
* MoreExpendableThanYou: Rogin to the Doctor.
* MutagenicGoo: The slime trail left by the Wirrn larva transforms Noah into a Wirrn.
* NotNowKiddo: Done to Sarah Jane. ''Twice.'' Eventually, the Doctor reveals he's doing this as a SecretTestOfCharacter, trying to make Sarah feel undervalued so she will rise to the challenge. In truth, the Doctor is very proud of her.
* NotThatKindOfDoctor: The Doctor claims that his is honorary, and that Sullivan can only treat sailors.
* ObstructiveBureaucrat: Harry isn't useful in medical emergencies despite being a Navy doctor, because he "is only qualified to work on sailors".
* OurMonstersAreWeird: The Wirrn has a truly bizarre multigenerational life-cycle that functions as The Virus and parasitism simultaneously. Wirrn larva are created through fertilising the skin of another species (non-sapient animals are used for this purpose on the Wirrn homeworld, but humans and presumably Time Lords work just as well) and converting their body and brain into that of a larva. The larva then pupates and develops into a fully-fledged Wirrn, a huge wasp-like creature, which gains all the knowledge its host knew. It then lays eggs containing larvae that hatch under its direct control, and any hosts they fertilise transfer the knowledge back to the swarm leader as well.
* PatrickStewartSpeech: See the page quote.
* PeekABooCorpse: Done as a CliffHanger with a Wirrn corpse rather than a human one.
* PeopleInRubberSuits: The larva was actually made out of green bubble wrap - but considering that bubble wrap had only just been invented (to the point where it wasn't even called 'bubble wrap' yet), the overall effect worked, if only for about five years after the episode's premiere. Supposedly the bubbles went 'pop-pop-pop' as the extras inched their way across stage reducing cast and crew to hysterics and the sound department to tears. Most of the scenes with the larva are recorded silently with incidental music over the top - if there's dialogue in the scene, a layer of smooth plastic is placed underneath the larva to reduce the likelihood of the bubbles bursting.
* TheReasonYouSuckSpeech: The Doctor gives one to Sarah Jane calculated to hit all of her {{Berserk Button}}s, in order to turn her [[ScreamingWoman screaming]] into screams of UnstoppableRage. (This was the Fourth Doctor's second story and so it serves as something of an EstablishingCharacterMoment for him - it is impossible to imagine the Third Doctor being this manipulative.)
--->'''Doctor''': Oh, stop whining, girl. You're useless.
--->'''Sarah''': Oh, Doctor..!
--->'''Doctor''': "Oh, Doctor", is that all you can say for yourself? Stupid, foolish girl. We should never have relied on you. I knew you'd let us down. That's the trouble with girls like you. You think you're tough, but when you're really up against it, you've no guts at all. Hundreds of lives at stake and you lie there, blubbing.
* SleeperStarship: Well, it's meant to be gone for 5 millennia.
* SolarFlareDisaster: Solar flares have made the Earth inhabitable, so the humans evacuated it in search of a new home.
* TransformationHorror: Noah finds himself slowly undergoing a horrifying transformation in a Wirrn after being infected by one.
* TheVirus: The Wirrn can work a lot like this.
* YouAreInCommandNow: Noah appoints Vira as the commander when he realises he's no longer able to.