Follow TV Tropes


Recap / Doctor Who S36 E4 "Knock Knock"

Go To

Doctor Who recap index
Twelfth Doctor Era
Series 10: CS | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | CS
<<< Series 9 | Series 11 >>>

Knock Knock
"Forgive me, but are you looking for somewhere to live?"note 
Click here to see the Magazine/Radio Times magazine poster for this episode:
Written by Mike Bartlett
Directed by Bill Andersonnote 
Air date: 6 May 2017

Shireen: So this house is eating people?
The Landlord: We must all pay our dues.
Bill: But not you?
The Landlord: Correct. I am the exception. For I am your landlord. You came here, you signed the contract. And now, it's time to pay.

The One With… the monster house... made of monsters.note 

Also, the one with Poirot.

Back in her own time and place, Bill Potts wants to move out of the flat she shares with her adoptive mother Moira and strike out on her own, but she and her five friends, all being students of little means, can't seem to find a decent place to live in a tight housing market. One day, the sextet is emerging from the student housing council in disappointment once again when a kindly older gentleman approaches with an irresistible offer...

The Doctor uses the TARDIS to help Bill move her belongings to the beautiful old house where she and her friends will each have a space of their own for dirt-cheap rent. But standing outside the house, listening to the wind blowing through the trees... the Doctor hears something that he realizes is not the wind.

To Bill's mortification, that night she and her friends (four of them, anyway — the other's been keeping to himself upstairs) discover the Doctor sneaking about the house, trying to figure out what it is that is making the place so noisy. The floors, the walls, they squeak all the time; it's an old house after all. Bill wishes her tutor (or, as she claims to her friends, "grandfather") would leave her be, let her have her own life. But she may not have it for much longer. Nor may her friends. What makes the house and its environs noisy is not the wind, or its age. It's something within the walls — within the wood, to be precise. Something that needs to feed, something the Landlord knows about, something that he can control for a purpose that will only be revealed if the Doctor and the others can make their way into the tower at the heart of the building...

David Suchet guest stars as the Landlord. Official trailer here.


  • Admiring the Abomination: When the first dryad crawls through the wood, the Doctor is quite taken with it. Not so much by The Swarm that follows.
  • Absent-Minded Professor: The Doctor doesn't realize immediately that the Landlord, a regular human, can't be the father of a woman whose life has been artificially extended for 70 years, and it takes Bill to point it out to him. He explains afterward that the brevity of human lifespans (compared to his own) had slipped his mind.
  • Action Insurance Gag: One of Bill's housemates laments "Bang goes the deposit!" as they watch the house collapse.
  • Amazingly Embarrassing Parents: Bill acts mortified when the Doctor is around her housemates. Her mates think he's a pretty cool dude.
  • And I Must Scream: Pavel's fate is being half absorbed into the house because his violin record is repeating. The Landlord considers releasing him to be fully absorbed a mercy.
  • Armor-Piercing Question: The Landlord snaps at the Doctor asking wouldn't he do whatever it takes to preserve the lives of his loved ones. The Doctor doesn't answer, and he takes that as an answer.
  • Bait-and-Switch:
    • The Doctor asks for Bill's phone after she complains that she has no reception, but rather than giving it the standard companion upgrade to "Universal Roaming", he just uses it to play music.
    • The students hear strange thumping and banging noises and nervously go to investigate, only to find the Doctor stumbling about in a cupboard.
  • Big Bad: The Landlord, AKA John.
  • Big Creepy-Crawlies: The "Dryads" (or woodlice) seem to be roughly the size of a fist. note 
  • Bittersweet Ending: Eliza finally ends her existence, taking her son with her, and manages to restore Bill's friends but she can't restore those who her son sacrificed before them. Also, the students lose all their stuff as well as their security deposit and still don't have a place to live.
  • Blessed with Suck: Eliza keeps living but is trapped as a wooden being and can't leave.
  • Bookcase Passage: The door to the tower is behind a bookcase. Paul knew that something like that would be in a spooky old house like this one.
  • Breather Episode: Set between the short-form arcs of Bill getting to know the Doctor and the Doctor's blindness/Monks Trilogy. While this story is a spooky one, all of Bill's friends make it out alive, the villain has a sympathetic motivation for his actions, its first half is heavy on comedy, and the Vault scene at the end just foreshadows the identity of its occupant rather than advances the arc.
  • Brick Joke: The Doctor smells the takeout Bill and her housemates are eating, and says he's in the mood for Chinese. At the end, he brings takeout to the Vault and offers to share it with the prisoner.
  • Cell Phones Are Useless: There's no cell phone reception in the house. Shireen makes note of this and says that it gives her a feeling of impending doom.
  • Chekhov's Gun:
    • A freshers' party in the park is mentioned near the start of the episode. Near the end, the Doctor uses a fireworks display from the party to remind Eliza of the joy of being alive.
    • The Landlord tells Bill that the house will preserve those it absorbs forever. When Eliza kills herself and her son at the end, she is able to restore Bill's dead roommates to how they were.
  • Claustrophobia: Felicity may be a sufferer, given how badly she freaks out about being trapped.
  • Continuity Nod:
  • Contrived Coincidence: The Landlord only rents out rooms once in every 20 years, yet in city of half a million residents, one of the new tenants just happens to be the Doctor's current companion.
  • Creepy Basement: The Doctor and Harry end up in the house's basement via an old lift. It gives the Doctor the clues he needed to figure out what's going on.
  • The Dead Have Names: The Doctor finds the personal effects, and written contracts, of people who came to live in the house. He throws some of their names at the Landlord the next time he encounters him.
  • Disposable Vagrant: In a deleted scene, the Landlord explains that he discovered the Dryads needed human sustenance when they devoured a vagrant who broke in.
  • Dramatic Thunder: There's a thunderstorm on the night that Bill and her housemates move in.
  • Driven to Suicide: Eliza, on finding out how she is being kept alive and realizing how her life will keep her trapped in the house, commands the Dryads to consume her and her son.
  • Even Bad Men Love Their Mamas: The Landlord is motivated out of a desire to keep his mother alive.
  • Everybody Lives: Eliza restores all of the students to life when she sacrifices herself and her son.
  • Family Relationship Switcheroo: Eliza is actually the Landlord's mother, not his daughter.
  • The Fog of Ages: The insects have been keeping Eliza alive, but they're not so good at preserving memories, so she doesn't even remember her actual relation to the Landlord. He takes advantage of this to pass himself off as her father, when he's actually her son.
  • Forbidden Chekhov's Gun: The Landlord tells the tenants that they're not to enter the tower, which they of course try to anyway.
  • Foreshadowing:
    • The Doctor mentions regeneration to Bill, but doesn't explain what it is. He seems particularly haunted by the subject, as he tends to be when he's nearing the end of one of his lives.
    • One of the students mentions it's the sort of house where you'd expect to find a Bookcase Passage. Sure enough, there is one.
  • Genre Blindness: Despite Bill's noted Genre Savviness, she steadfastly refuses to believe that there's anything wrong with the house until after her friends start getting eaten.
  • Ghost Butler: Doors start slamming shut and shutters close over the windows once the dying starts.
  • Gothic Horror: The episode has strong elements of this, given the creepy old house with built-in secrets, and the screwed-up family relationship that turns out to be at the root of it.
  • Haunted House: The mansion gives off this vibe, with unexplained scratching noises, doors that seal themselves shut, and shutters closing by themselves.
  • Hell Is That Noise: The constant creaking in the house.
  • Hope Spot: Felicity manages to escape from the house as it seals itself, but then gets eaten in the garden.
  • Human Architecture Horror: Pavel is discovered halfway through the process of being absorbed into a wall.
  • Immortality Immorality: The Landlord feeds six students to the Dryads every 20 years in exchange for the eternal life of his mother.
  • Incompatible Orientation: Paul tries to flirt with Bill, and receives a truthful Sorry, I'm Gay. He's relieved that it's this and not that she's rejecting him because she doesn't like him.
  • Internal Homage: The establishing shots of a thunderstorm over a creepy Victorian mansion (with a tower added by CGI) are similar to those in "Ghost Light". One of Bill's mates also says "Wicked!"
  • Life Drinker: The Dryads consume people, which enables Eliza to keep living.
  • Liquid Assets: Once every twenty years, the Landlord lures six students to the house, so their life force can be drained and used to keep Eliza alive.
  • Load-Bearing Boss: With Eliza's death (and presumably the insects') the house starts to come apart and collapse.
  • Love Makes You Evil: The Landlord has done everything out of love for his mother.
  • Luxury Prison Suite: Nardole is shocked on realising the Doctor has allowed the prisoner inside the Vault to have a piano. And he's bringing Chinese food as well.
  • Lyrical Dissonance: The prisoner inside the Vault is playing "Für Elise" on a piano, but stops on a discordant note on realising the Doctor is outside. The Doctor says he's come with food and another story to tell, but there's no response until he adds that the story involves a lot of young people getting eaten. The piano then starts up again with "Pop Goes the Weasel".
  • Madwoman in the Attic: The Landlord is keeping his alien-converted and amnesiac mother trapped in the tower. There's also the suggestion that the prisoner of the Vault is one of these, given that it reacts enthusiastically to the prospect of hearing about people being eaten.
  • Mind-Control Music: Various sounds can control the Dryads.
  • Momma's Boy: The Landlord, who seems to be psychologically stuck on keeping his mother Eliza alive (possibly because he was only a child when she was dying and the insects saved her). She's horrified when she finds out what's happening.
  • More Expendable Than You: Played for laughs when Paul Got Volunteered to investigate the creepy noises, because he's the biggest and most expendable. Bill then volunteers for real, and everyone else immediately follows behind her.
  • Motifs: Several specific to Series 10:
    • Mothers: Bill puts a photo of her mum on the wall of her room and talks to it, and The Reveal is that the Landlord has done his dirty deeds all to keep his mother alive.
    • Imprisonment/Release: Victims of the Dryads are absorbed and trapped in the walls on the way to their lifeforce being completely drained, while Eliza has been locked away in the tower all this time. When she realizes what's really been going on, she tasks the Dryads to not only let her die, but to free Bill's friends as well. In the final scene, the Doctor visits the resident of the Vault and notes that they're both prisoners.
    • Exploitation: The Landlord realized the Dryads could keep Eliza alive, figured out how it worked and how to control them, and then started luring victims (specifically youths with little means desperate for homes) to the house.
    • "Villains" who aren't evil: The Dryads, who are just a tool of the Landlord.
    • Swarming creatures: The Dryads.
    • Hidden threats: The Dryads hiding within the walls of the house.
    • Truth: The climax of the episode comes when Bill and the Doctor (in that order) figure out and reveal to Eliza the truth about her and her "father".
    • The value of each individual life: The Landlord is so desperate to keep Eliza alive that he willingly lures and sacrifices innocent youths to the Dryads.
  • Mundane Utility: The Doctor uses the TARDIS to move Bill's possessions to her new house.
  • My God, What Have I Done?: When Eliza's mind gets more clarity, she changes her stance from always listening to her "father" to coming to terms with the fact she's been taking lives for decades.
  • Mythology Gag: When the students first hear the strange noises, they jokingly suggest it's a massive spider or a doll come to life.
  • The Nameless:
    • Bill points out that "Time Lord" is not the name of a species. In fact, we've seen on Gallifrey that the Time Lords are only the ruling hierarchy. So what is the Doctor's species?
    • The Doctor hasn't encountered the crawly creatures before, so as usual he just makes up a name.
  • Nature Spirit: The Doctor surmises the insects are the source of legends such as dryads and tree nymphs. As they can control wood, turned a woman into wood with a prolonged life, and bound her existence to it, it's plausible.
  • Non-Answer: The Doctor sidesteps Bill's question of what "regenerated" means when he brings it up.
  • Noodle Incident: The Doctor mentions that he once met musician Quincy Jones... and that Jones' bassist during that meeting turned out to be an alien in human disguise. He doesn't seem to elaborate beyond that.
  • No Ontological Inertia: Eliza commands the Dryads to release Bill's housemates, which causes them to be restored to life despite being sucked on for a little while.
  • Offing the Offspring: Eliza is tragically forced to do this to her own son, as well as ending her own life, to keep him from killing Bill and the Doctor.
  • Ominous Music Box Tune: Shireen finds a music box in Eliza's room. The tune and Eliza's movements quickly startle her into closing it. The Landlord has used it 70 years prior as a trigger for the dryads to preserve his mother.
  • Parental Substitute: The Doctor helps Bill move house and identifies as her father.
  • Plant Person: Eliza is turned into wood by the dryads.
  • Powered by a Forsaken Child: For Eliza to live, the Dryads need to eat people.
  • Power-Upgrading Deformation: Eliza keeps living, but was turned into wood by the Dryads.
  • Psychopathic Manchild: The Landlord is a somewhat sympathetic Type C. He conducts himself to the housemates and the doctor like an adult. But his interactions with his mother show just how emotionally stunted he is at heart, and in her presence degrades into a stubborn, petulant Mood-Swinger determined to save his dying mother from the Reaper at all costs.
  • Pull the Thread: It's Bill who sees the holes in the Caretaker's story. He's not old enough to be Eliza's father, and bringing insects from the garden to show a sick person is something a boy would do, not a father.
  • Redemption Rejection: After discovering the truth of what her son did and seeing the world outside for the first time in decades, Eliza prepares to have the Dryads devour her, and tells the Landlord to make the most of his remaining years. The Landlord refuses, and tries to make them turn on the Doctor and Bill, in turn causing Eliza to have them devour her and her son.
  • Red Herring: The Doctor's conspicuous Exposition about Time Lords at the episode's beginning, followed by the villain being a distinguished actor playing an eccentric old man known only as "The [NOUN]", hints Time Lords will play a role in the plot. This turns out not to be the case.
  • Regularly Scheduled Evil: Tenants of the house have been disappearing at 20-year intervals: 2017, 1997, 1977...
  • Relatively Flimsy Excuse: Bill claims to her housemates that the Doctor is her grandfather. He prefers "father" because he is not nearly old enough to be a grandfather, obviously.
  • The Reveal: The third act contains one shocking plot twist about Eliza. She was never the Landlord's daughter, but rather, his mother. It reframes the Landlord's actions in a new light, from someone wanting to save the one he loves, to essentially killing countless tenants just to protect the person who brought him into this world.
  • Shout-Out: The Radio Times poster alludes to David Suchet starring in Poirot via its art deco style and the man's costume.
  • The Sleepless: The Doctor claims he only sleeps after he regenerates or has a big lunch.
  • Sorry, I'm Gay: Bill tells this to Paul when she notices he's interested in her. He's pretty happy to hear that he never stood a chance because it means he didn't fail.
  • Stealth Hi/Bye: The Landlord twice pulls this on Bill and her housemates. Given his control of the insects, he can probably move right through the walls if he wants.
  • Supernaturally Young Parent: The Landlord is initially thought to be Eliza's father, but is in reality her son, who has been keeping her youthful and immortal artificially through the use of the dryads. He passes himself off as Eliza's father in order to explain away the fact that he looks decades older than his mother.
  • The Symbiote: The dryads are insects capable of merging with wood on a cellular level that can extend this ability to other lifeforms, turning them into wood and prolonging their lifespan.
  • Talking the Monster to Death: The Landlord's mother Eliza has become some kind of human/wood-nymph hybrid, and the Doctor convinces her that her meager existence isn't worth having to ritually murder people for.
  • Teacher/Student Romance: Bill tells her housemates that the Doctor is her grandfather, because to have her tutor so involved in her personal life would cause suspicions of this.
  • Terrible Interviewees Montage: The episode opens with Bill and her prospective housemates trying to find somewhere to live, presented as a montage of terrible houses.
  • Too Good to Be True: Bill and her housemates, after unsuccessfully house-hunting, are suddenly offered a very roomy old house with more space than they need, amazingly cheap. Of course there's a catch...
  • Tragic Villain: The Landlord — driven to sacrifice innocent young people by his love for his mother.
  • Tranquil Fury: When the Doctor first confronts the Landlord over the disappearance of the roommates he gives an unsmile as he asks where they are.
  • Undeath Always Ends: Eliza's elongated life comes to an end when she is told the whole truth, and stops the cycle of Liquid Assets.
  • The Unreveal: The Doctor brings takeout to the prisoner in the Vault, and offers to tell them about the events of the episode (disturbingly, when he mentions that a lot of young people got eaten, the prisoner's piano playing changes from "Für Elise" to the cheerful "Pop Goes the Weasel"). The episode ends on him entering the Vault.
  • Weirdness Magnet: Nardole points out that the Doctor doesn't have to go gallivanting around time and space to look for monsters, as there are plenty that want to kill him right here on Earth.
  • Wham Line: When the Doctor and Bill confront the Landlord and Eliza, the Doctor surmises something about Eliza's real identity, after initially believing that the Landlord was her father.
    The Doctor: Your father would have had better things to do than playing with insects in the garden. But he isn't your father. When you were ill, he was sent out of the house by the doctors who are failing to save his mother!
  • What Happened to the Mouse?: Bill hung her framed picture of her mother on the wall of her bedroom. The house subsequently collapsed into a cloud of bugs. Did Bill lose what, until recently, had been her only photo of her mum?
  • When Trees Attack: Felicity gets eaten by a tree in the garden when she attempts to flee the house.
  • Who Wants to Live Forever?: As wood, at least. The Dryads are keeping Eliza safe from her illness, but they can't preserve her memories, or give her or her son the joy of being truly alive.