Let me just say that two adventures in, this is a pretty good season.
Ark in Space picks up where Robot left off, with the Tardis landing after abandoning the poor Brigadier without so much as a goodbye. And they land on a space station.
By walking through three rooms and a really neat hallway, they surmise that they're on a station meant to hold the remains of humanity after some global disaster-- they're all in cryo, waiting to be revived 5,000 years after they went under. Only it's been at least 10,000 years, and there's something weird and green and slimy lurking about the place. So, as the designated Ankle-Twister, Sarah-Jane gets herself in trouble and spends most of the first episode or two unconscious, first from oxygen deprivation, which almost gets Harry, too, but doesn't do much against the Doctor (I love when he doesn't act human)-- then gets transmatted away and put in cryo by a computer glitch that assumes she's one of the ones that are supposed to have already been there. So they have to find her, and then find out what to do about her.
Looking for a revival kit of some sort, they find the mummified husk of a giant bug, and then Vira, cheif medical officer, is awakened by the computer and tells them what's going on-- and they tell her what's gone wrong.
So Sarah's saved, and wearing something other than that horrible purple dress in the previous episode, and they have to go up against the bug-slugs, which are the larval stage of the big husk they found-- and which reach the adult stage by taking over human bodies, and who plan to use the sleeping remains of humanity to do just that. The Doctor has to save the few people who've already awoken, himself and his companions, and do it in such a way that the rest of humanity is safe, too. Luckily, the commander of the mission, though taken over by the bugs and fully transformed, remembers that his human self was in love with Vira, and leads the bugs atray when he realizes he can't get her to come across and stay with him, eating the people they were supposed to protect.
A great story, The sum-ups at the beginning of each episode only went back a few seconds instead of whole minutes, and action happened right after getting off the tardis-- good signs of a solid plot with alot to say. The Doctor widgets with the wiring, Sarah Jane travels through very small conduits because she's the only one who can, Harry gets to learn a little of futuristic medicine, and all the conversations are dense and engaging and useful to the plot. And, again, the Doctor shines in caring about the fate of his companions as much as he cares about the fate of humanity, and his fondness for Ms Smith makes him utterly charming, while his disregard for Harry so far makes him amusing.
At the end, Sarah Jane puts on the first of what I know will be a long succession of ugly raincoats, and they head down to the surface to check things out before the colonists come back down.