Doctor Who: Knock Knock

"Landline??? What is this- Scotland?"

So that's four good episodes in a row for this quietly impressive season; we get a solid bit of teatime horror from Mike Bartlett, a writer new to Who but not to telly, more top chemistry from Bill and a bizarrely Tom-like Doctor, Hercule Poirot being splendidly sinister, and a satisfying and emotional conclusion. It's a story-of-the-week, yes, but that's what Doctor Who should be.

As with Clara, Bill maintains her life when not travelling in the TARDIS- a bit of a Moffat-era trope- and we're introduced to her uni housemates; it's interesting to ponder whether we'll be seeing any of them. It's too soon to get to know any of them yet, though, even if one of them is supposed to be Harry Sullivan's grandson. We know, of course, that this spacious luxury house offered as a student house at a knock-down price is going to come with a catch, but the fun is in the finding out, and fun it is. We get a kind of slasher narrative with the big alien woodlice (Are they alien or not? For the second episode in a row it's left deliberately ambiguous whether or not the monster is in fact just an undiscovered terrestrial beast. Is this an arc thing?) picking off flatmates one by one, but the fact they are all restored keeps things nicely kid-friendly. And the resolution is genuinely excellent. The episode as a whole is a subtle masterclass in how to write and structure an episode of television.

I like the obvious throwback to Susan early on, with Bill pretending the Doctor is her "grandfather", and her embarrassment at his hanging around in her fourth-wall breaking way ("Basically this is the bit of my life that you're not in"), and I love Bill's characteristic skewering of Time Lord pomposity as soon as she hears them mentioned. It's a good opportunity to seed the idea of regeneration early in the season though.

The end contains a half-revelation: the Vault appears to contain a person, or at any rate something both able to play Beethoven on the piano and with an interest in gory stories. I think I may have an idea of who it might be...