‘There’s a haunted house and woodlice from space. And lots of young people get eaten.’ After the obligatory trips in time and space, like Rose and Donna before her it’s Bill’s moment to come back down to Earth in time for her fourth episode. This leans into Bill’s backstory, as she moves out of her step-mother’s house and in with university friends – and has to confront an enemy with his own mother issues.

I love the set-up of this, the relative normality of Bill’s life compared to Clara or Amy’s. I’m not sure we ever saw either of them interacting with their friends (Danny and Rory don’t count). Again, kudos for Moffat for doing something different even though he’s on his lap of honour. The first half of is brilliant: Bill getting the Doctor to give her ‘a lift’ to move her stuff into her suspiciously-cheap new accommodation, and her increasingly sour-faced attempts to keep the Doctor away from her new housemates – who all think he’s cooler than she is. In the background, one of the housemates is missing, and something seems to be living in the walls. The reveal of Pavel being absorbed into the wood panelling is strikingly grisly.

The pay-off isn’t quite as good, though there are still things to enjoy. Eliza, looking like a wooden Weeping Angel, is creepy, and it needed a performer of David Suchet’s abilities to mostly sell the pivot from ultra-sinister landlord to tantrumming child. Even so, I wasn’t totally sold on woodlice that turn people into wood (though I massively enjoyed the Doctor’s bafflement that not everyone shared his fascination with bugs) or eat then reconstitute the housemates. Alien plants that absorb people into them, I could buy; alien woodlice that eat people, I could buy. The two together is like finding a robot Yeti in the London Underground (without The Abominable Snowmen to set it up).

I appreciate what Knock Knock is doing, particularly Mackie’s performance, and Bill’s empathy for the landlord’s love for his mother and desire to save her. The relationships between the housemates outclass Class, and Capaldi gets another script that gives him chances to be heroic and eccentric. It’s a much more convincing haunted house story than Hide.

Next Time: Oyxgen