When Bill (Pearl Mackie) and her friends get a screaming deal on a rental house in “Knock Knock,” the latest episode of Doctor Who, the Doctor (Peter Capaldi) is sure something is amiss. As usual, he’s right.
The episode opens with Bill’s friend Shireen (Mandeep Dhillon) introducing Bill to four other people, Felicity (Alice Hewkin), Paul (Ben Presley), Harry (Colin Ryan) and Pavel (Bart Suavek), as their new housemate. The six are moving in together, and after having no luck finding a suitable place with their estate agent, they encounter a stranger (David Suchet, a.k.a. Hercule Poirot in all the Agatha Christie movies you’ve ever seen on PBS) who offers them an estate at a literally too-good-to-be-true rate.
The Doctor helps Bill move her things to the new place with the TARDIS, which she allows him to land in her bedroom at her foster mother’s to collect her things but makes him park just outside the estate’s grounds on the other end for the dual reasons of not wanting to make a weird impression on her new housemates and preventing the TARDIS from giving them a shortcut out of the inevitable danger they’ll find inside.
Housemate Pavel is the only one who has already arrived before Bill and the others. He came the night before, and just after turning on his turntable in his new room, we heard him screaming in terror. Now his bedroom door is closed, his turntable is playing one snippet of music on infinite repeat and the housemates who know him best brush off his failure to appear to greet anyone as typical behavior for him. (Him or anyone else who succumbs early in a horror movie.)
From the minute he steps onto the estate’s grounds with Bill, the Doctor senses something’s off. Bill insists that the house is just a great deal because it’s shabby and he doesn’t need to come inside to embarrass her. He pushes his way in with some of her belongings anyway, and she introduces him to everyone as her grandfather. (Remember in the first episode of this season where he had a photo of his granddaughter on his desk at the university *and* appeared in an old photo of Bill’s mom? Maybe he IS her grandfather– or great grandfather– somehow!)
When Bill finally gets him to go away, she and her new friends start settling in. The house is unusually creaky, and everyone is a smidge on edge. Nevertheless, they put their things away and congregate in the parlor to eat takeout Chinese together and enjoy their first night in the new place.
While they’re eating, though, they start hearing weird noises from the kitchen. Bill volunteers to check it out, and the rest of the crew follows behind. The noises are coming from a cupboard, and when they open it, they find… the Doctor! Of course.
He emerges with an ancient oil-burning heater and informs them that their new home is missing nearly every modern convenience. Its electric system hasn’t been updated since the 1930s, there’s no central heating, no cell reception, etc. He tells them to get a new house, but they’re insistent that although they acknowledge its flaws, student housing options are rarely glamorous and this one has big bedrooms and a low rent.
When they return to the parlor, they’re surprised to find their new landlord sort of lurking about in there. He claims to be looking in on them, but he is weirdly affectionate with the walls, caressing them and pinging them with a tuning fork, and when he leaves, he seems to disappear into thin air.
Bill tries to kick the Doctor out again, but he refuses and says he’ll hang downstairs with Harry and Felicity while Bill, Paul and Shireen head up to bed.
As soon as they split up, things start getting weirder. Bill and Shireen say goodnight to Paul (with Bill first needing to let him down easy because she mostly goes for girls), and as soon as he closes his bedroom door, they hear him screaming. They’re frightened, but he’d been trying to wig them out all the way upstairs, so at first they’re willing to write it off as a prank– until they get a responding knock from his door that quickly escalates from a reassuring sound saying their friend is fine to a mocking knock that begins coming from every wooden surface in every direction. They make a run for it, heading upstairs as all the doors and shutters in the house begin sealing themselves.
Downstairs, the Doctor is the first to become aware of this sealing-in. Felicity is so freaked out by being trapped that she pushes her way out of a window before the shutters have completely closed… only to find herself consumed by a tree outside. Hearing her screams from where they’ve become trapped in the kitchen, Harry begins to panic a bit while the Doctor starts puzzling out what’s happening. He quickly lands on some kind of wood spirit, and he begins pestering a cupboard door in an effort to provoke whatever they’re facing into showing itself. He’s successful in getting one beetle-like creature to emerge from the wood itself.
Now he posits that there’s some kind of alien wood lice infesting the house, and that they’re literally absorbing the occupants into the wood. While he’s reveling in his cleverness and trying to catch the one wood louse he’s seen, Harry notices a swarm of the creatures emerging from a wall. Fortunately, the cupboard the Doctor popped out of earlier is actually an elevator, and they’re able to escape to the basement in it.
In the basement, the Doctor and Harry discover boxes of belongings stored along with the rental contracts of previous tenants– six at a time, every 20 years for 70 years. As they explore the archive, the landlord appears. The Doctor gets him to admit that he uses the wood lice to help keep his daughter alive, and that giving them humans to eat every 20 years is what allows him and his daughter to survive there with the creatures’ help. The Doctor figures out that the man’s daughter is in the house somewhere– in the tower that the landlord has forbidden anyone from entering.
While the Doctor and the landlord talk, Harry tries to make a run for it, but his foot disappears into a stair step and the creatures swarm up from it and apparently devour him. The Doctor convinces the landlord not to feed him to the lice, too, asserting that he might be able to help the man’s daughter if he can see her.
Bill and Shireen have already found her, though. After discovering Pavel half-way consumed by his bedroom wall and watching the landlord finish him off, the girls run for their lives.
Bill guesses correctly that a bookcase positioned in a hallway where a door to the tower would logically be is actually a concealed door, and when she tugs on the correct book, the bookcase swings open to reveal a spiral staircase. Bill and Shireen run up it and find a wooden screen, from behind which the landlord’s daughter, Eliza (Mariah Gale), steps. She is a wooden woman.
While processing what they’re looking at and trying to decide whether Eliza is more terrifying than the things they’re running from, Shireen steps on one of the bugs. It doesn’t take long for her mistake to become clear, as she, too, is swarmed and disappears into the wood.
At this moment, the Doctor and the landlord enter, and a shaken Bill tells the Doctor about Shireen before the Doctor gives her the extreme Cliff’s Notes version of everything he’s figured out. Then he begins asking Eliza and the landlord questions about the origin of her condition and their situation. He learns that the landlord found some insects in the garden and brought them to his ailing daughter to cheer her up. The next morning, he discovered that her health had improved and one of her arms had turned to living wood. When he understood that the mysterious beetles were responsible, he began training and caring for them, and in exchange they’d kept Eliza alive for 70 years.
Bill notices a flaw in this story: What grown man would think to bring insects in from the garden to amuse a dying adult daughter? The Doctor makes the leap that over all the years of being isolated and living in secret, Eliza has forgotten that the landlord is not her father– he’s her son.
When she remembers this, Eliza is heartbroken over all the young people she and the house have consumed. She’d been doing as the landlord said because she believed that her father would know best, but when their roles are reversed she realizes that instead she’s allowed them both to become monsters in order to artificially prolong her life.
The landlord is irate. He summons the creatures to destroy the Doctor and Bill, but the Doctor appeals to Eliza and convinces her that as the parent, she’s in control. She attempts to manipulate the swarming beetles and discovers that this is indeed the case. Then she embraces her son, tells him that their time is over and allows the beetles and the house to consume them both.
In a refreshing twist on the horror movie ending, Eliza/the house then regurgitates all of Bill’s housemates, and the lot of them escape with the Doctor before the house is consumed altogether by the alien wood lice. (Along with all of their possessions, I guess.)
Later, safely returned from this Earth-bound adventure, the Doctor joins Nardole (Matt Lucas) at the vault beneath the university. Nardole tells him that the guest within has been restless, and then a piano begins to play. Nardole is incensed that the Doctor has put a piano in with their prisoner. The Doctor dismisses him and then cordially offers the being in the vault a Mexican food dinner and a story about a haunted house that eats young people.
Notable in this episode: The Doctor describes himself to Bill as a Timelord for the first time while he’s moving her belongings to the house. She doesn’t get a lot of detail out of him, but he does mention regeneration. After doing so, he immediately looks as though he regrets it and Bill wants to know what it is. He deftly changes the subject, but that’s the first on-screen evidence that the end for Capaldi’s Doctor is nigh…
Theory: I bet it’s the Master in the vault.