“Knock Knock” is the only episode from this season of Doctor Who to be written by someone new to the show’s universe. Playwright Mike Bartlett, creator of the acclaimed 2015 drama series Doctor Foster, contributes an atmospheric haunted-house story which builds up the tension nicely before, unfortunately, dissipating it a little too easily at the climax. Along the way, Bartlett provides further development of the relationship between the Doctor (Peter Capaldi) and Bill (Pearl Mackie): This time, it’s as if the Doctor finds himself getting drawn into Bill’s life rather than the other way around.
As the episode opens, Bill has decided to move out of her foster mother’s house. She and her friend, Shireen (Mandeep Dhillon), are presented with the opportunity to share a dilapidated old house with four other students. They’re not put off by the strange creaks emanating from the floorboards and the wall paneling, and Bill enlists the Doctor’s help to move her belongings into the place. She soon regrets that, though, when he becomes intrigued with the building and deaf to her hints that she’d like him to leave. Capaldi and Mackie ably handle the light-hearted banter between the Doctor and Bill as the former embarrasses the latter in front of her peers over her taste in music, while in turn she pretends he’s her grandfather. This last development provides a slight frisson, as we know that the Doctor has a photo of his real granddaughter, Susan, on the desk in his office, and we saw in “The Pilot” that he finds an echo of that relationship in his mentoring of Bill.
Of course, since one of the students doesn’t even make it to the opening titles before suffering a nasty off-screen fate, we know the old house contains something more menacing than the odd creaking floorboard. As darkness falls and two more of Bill’s friends disappear, director Bill Anderson effectively uses simple devices like unexplained sounds, and doors and shutters suddenly slamming for no reason, to make this haunted building a worthy companion to the similar ones in 2007’s “Blink” and 2013’s “Hide”. An effectively spooky moment comes when Shireen and Bill tap lightly on one of the bedroom doors, only to be answered by a fusillade of loud knocks from multiple directions. There’s also a clever fake-out with Bill nervously opening a door in the kitchen behind which strange noises are coming, only to discover the Doctor hadn’t gone after all, but is poking around on his own.
The episode’s centerpiece is the terrific performance given by its high-profile guest star, David Suchet. The definitive Hercule Poirot appears here in the role of the mysterious landlord (not even given a name) who’s willing to let six students rent his old mansion on oddly generous terms. On paper, there’s nothing particularly distinctive about the character, as the eccentric stranger, who obviously knows more than he’s telling, is a stereotype in stories like this, either warning the protagonists away from the sinister location or (as in this case) drawing them in. It’s Suchet’s magnetic presence that makes the character compelling, able to switch instantly from warmth and concern to a snarled “You don’t” when asked how to get in to the tower attached to the house, and then back again to amiability.
As for the students, they’re sketched in quickly but well, making for a believable group of friends. They’re hardly complex characters, but Shireen and Harry (Colin Ryan) are substantial enough: Paired with Bill and the Doctor, respectively, they allow Bartlett to have two separate plot strands running during the middle part of the episode as they investigate and eventually discover the nature of the menace in the house. Alien creatures looking rather like large woodlice and able to phase through matter are infesting the floors and walls. Bill sees them swarm over Shireen (rather like the Vardies in “Smile”) and draw her into the floor, joining all the previous victims that the landlord has delivered to them over the decades.
In the tower, Bill and the Doctor discover what the landlord has been protecting: a woman named Eliza (Mariah Gale), supposedly his daughter, whose flesh has been transformed into wood by the creatures inside the house, and who’s being kept alive by energy taken from their victims. In a clever use of the running gag about how Capaldi’s Doctor gets confused about human ageing, he fails to notice that the landlord must have been a boy when Eliza first encountered the creatures, but Bill picks up on the discrepancy immediately. Eliza is actually the landlord’s mother; the boy who saw her horrifyingly transformed has grown old and never had a life of his own while single-mindedly keeping her preserved.
It’s good to have what seemed like a straightforward “monster” story turn into something with more emotional complexity to it, but the effectiveness of this scene is really down to Suchet’s skill. He shows perfectly the vulnerability and pathos breaking through the brittle surface as the Doctor appeals to Eliza, and the landlord essentially returns to being a scared little boy. After this, the actual ending is rushed and rather a letdown, as Eliza takes control of the creatures and, even as they destroy her and her son, somehow manages to reverse all the apparent deaths of Bill’s friends. They run outside as the house begins tumbling down, and then more or less shrug the whole incident off with a joke about losing their deposit. The Doctor notes that it’s back to the estate agent for them, and simply walks away.
As with last week’s episode, the final few minutes are devoted solely to the ongoing season-arc plot, as the Doctor brings dinner for whoever’s inside his mysterious vault—along with a story about a haunted house that eats people. It’s an intriguing scene in itself, but the way the Doctor has so quickly moved on leaves the episode feeling superficial: What could have been a disturbing experience becomes just another day at the office.
Next Week: The Doctor, Bill, and Nardole find terror in deep space, in “Oxygen.”
Classic Doctor Who Recommendation: Some even more monstrous alien woodlice can be found in 1984’s “Frontios,” starring Peter Davison, Janet Fielding, and Mark Strickson.
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