Doctor Who/Recap/S12/E02 The Ark in Space

"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."

- The Doctor

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 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.

Tropes
""It may be irrational of me, but humans are quite my favorite species.""
 * Air Vent Passageway: Sarah Jane is the only one thin enough to get through the vent.
 * Apocalypse How: Solar flares toasted the Earth; probably rating around a Class 4 (biosphere extinction).
 * The Ark
 * Big Creepy Crawlies
 * Body Horror: Noah's transformation.
 * Break Her Heart to Save Her: The Doctor intentionally insults Sarah Jane and hurts her feelings in order to help her achieve the Air Vent Passageway escape. Needless to say, he doesn't mean it.
 * Butt Monkey: 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?"
 * Deadpan Snarker: Rogin
 * Decontamination Chamber
 * Earth That Was: 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.
 * Executive Meddling: In the orignal script The Wirrn were simply ejected from the Ark in the shuttle. However the BBC feared that the possiblity of them surviving would frighten younger viewers, forcing Holmes to kill them off at the end.
 * Heroic Sacrifice:
 * Humans Are Bastards: 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 largescale misery for another species.
 * Humans Are Special: See the page quote.


 * I Know You're in There Somewhere Fight: 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.
 * More Expendable Than You:
 * Not Now Kiddo: Done to Sarah Jane. Twice.
 * Not That Kind of Doctor: The Doctor claims that his is honorary, and Sullivan can only treat sailors.
 * Peek a Boo Corpse: Done as a Cliff Hanger with a Wirrn corpse rather than a human one.
 * Special Effect Failure: The larvae form of the Wirrn is done with green-painted bubblewrap (which was new at the time, so less well-known to audiences).
 * The Virus