Knock Knock (TV story)

 was the fourth episode of the tenth series of Doctor Who produced by BBC Wales. This was the first Doctor Who story to be made available with a binaural 360 soundscape, released on iPlayer.

The episode expands the Doctor and Bill's relationship briefly when he tells her about the Time Lords, the alien race he belongs to and quickly mentions regeneration to her, but doesn't explain what regeneration actually is to her.

It also makes a reference back to the Doctor's granddaughter Susan Foreman, as Bill passes the Doctor off as her grandfather and refers to him as such. She has also told her friends about him; although, the Doctor doesn't seem to have much of a problem with it.

The Vault is also implied to not just have the mass it appears to have, instead being dimensionally transcendental. The prisoner inside is heard playing a piano the Doctor gave them. Nardole also suggests that the prisoner is aware of when the Doctor is starting to neglect looking after them.

Synopsis
Bill and her friends rent an old house to live in, but the floorboards and the walls are creaking, and there's a creepy Landlord lurking around. Can the Twelfth Doctor save the day as creatures come crawling out of the wood?

Plot
Bill opens her door to find her friends outside. They head to the rel-estate office to find a place to rent together. However, the agent that helps them keeps finding places that are less than satisfactory. They head out to try somewhere else, only to be met by an elderly man named John, who offers to help them find a place. He shows them to an old house, which they assume will cost them a lot to rent; he assures them that rent will be cheap, telling them the tower is off limits.

Everyone explores the house, finding the rooms acceptable. Pavel asks to move that night as his host parents are kicking him out. The Landlord lets him, getting everyone to sign a contract. That night, Pavel plays music in his room, only to be surprised by something horrifying.

The next day, Bill is stacking up her belongings in boxes in her room. After everything is in on corner, she looks at her phone and counts down. The TARDIS appears over the boxes, which end up inside. The Doctor opens the door, surprised, thinking Bill had a lot more belongings than that.

Bill enters the TARDIS, suggesting that the Doctor offer his TARDIS as a moving service or package delivery. The Doctor is offended at the idea, stating that he's a Time Lord, confusing Bill; he explains that's what his species is called. Bill laughs at the name of the Doctor's species, noting how posh it sounds. The Doctor notes that's why he ran away from his people; he couldn't stand all that pompous attitude. Bill asks if Time Lords wear robes and hats. The Doctor tells her the robes are true, but Time Lords tend to wear big collars instead of hats.

When asked if he needs the address to find the house, the Doctor scoffs; however, he then relents and tells Bill to type it in so the TARDIS can land there. She asks him where he lives, telling the Doctor that everyone needs sleep. The Doctor tells her that Time Lords don't need sleep, except after big meals and regenerations. Bill is confused by his words, but the Doctor tells her that just knowing he's a Time Lord is enough for now.

The TARDIS lands outside of the house, with the Doctor confused as to how the rent can be so cheap. Bill thanks the Doctor for helping her, telling him he can leave once her boxes are out of the TARDIS. However, the Doctor has noticed something off and decides to help Bill move her stuff.

Inside, the Doctor is greeted by Shireen, who knows about him. Bill passes the Doctor off as her grandfather, despite his protests. Felicity, Paul and Harry join them, having also been told who the Doctor is. Bill tries to get rid of the Doctor, who seems to relent and leaves the house.

That night, everyone notices that they somehow do not get signals on their mobile phones. They hear noises like something running upstairs. Hearing banging from the basement, all six investigate. However, the door opens by itself, to reveal the Doctor, illuminated by his sonic screwdriver. Bill notes she thought he went home. The Doctor ignores the comment, telling the kids that there is no washer and dryer, no central heating and that the outlets will not take their devices. The entire house is suited only for the 1940s. Shireen notes the same thing, thinking it was only her room; she decides to call the landlord.

Everyone heads into the sitting room, where the Landlord is suddenly waiting. He states he came by to check on things; the kids list of complaints, to which he states he will get to eventually. Taking note of the Doctor, the Landlord is told the cover story about him being Bill's grandfather. The Landlord guesses that he's helping with relocating Bill; the Doctor agrees. Seemingly remembering a bad memory, the Landlord states there is no worse feeling that than leaving children to fend for themselves. The Doctor thinks on these words, remembering when he did so. The Landlord states that he's lucky to have a daughter that is still under his protection; he leaves for the night. When Shireen attempts to open the door to follow him, the Landlord has seemingly disappeared.

Bill tries getting the Doctor to leave, by suggesting he sleep in "the car"; however, the Doctor instead decides to stay up with Felicity and Harry to listen to some music. Seeing she can't win, Bill decides to head to bed, followed by Shireen and Paul. Paul tries to ask Bill out, but she tells him she's gay; humbly, Paul notes he never had a chance. He heads into his room, messing with Felicity's fear of the house by making creaking noises on the wood. Once he shuts his door, Bill realizes that Felicity fancies Paul. At that moment, Paul is heard screaming in terror. After a moment, they think he's messing with them; however, when they attempt to open his door, they find it stuck.

Downstairs, Shireen and Harry ask the Doctor what he thinks of the music playing on her phone. He notes that it reminds him of Quincy Jones, whom he once filled in for. The bass player for Quincy's band turned out to be a killer Voc Robot in disguise; what's worse is that he couldn't even play. He then directs their attention to the door, which no longer has any open space between the entrance and the doors; they have been sealed in. Bill and Felicity join them, curious about the happenings in the house.

The Doctor has them go check on Pavel, while he, Felicity and Harry find a way out of the house. This leads the Doctor's group to the kitchen, where the shutters are rapidly shutting. Felicity panics, grabbing the shutters to stop it from sealing her in, and jumps out the window. Running, Felicity tries dialing 999 for assistance, but makes the mistake of resting on a tree. It absorbs her, as she screams in horror. Hearing music still playing on a loop in Pavel's room, the two girls enter to find Pavel partially absorbed into the wall. Bill goes to turn off the music, but Pavel gives off a moan that suggests not to. The Landlord suddenly appears, shutting off the record and using a tuning fork on the wall; Pavel is absorbed completely. He tells them that Pavel is now at peace, one with the house. The Landlord further states that everyone must pay their dues, and the six signed a contract.

The two race out of the room and down the hall to a bookcase; deciding it must open a way into the tower, Bill and Shireen pulls books off until they find a switch disguised as one and pull it. A way opens into the tower and they run up into what appears to be an old bedroom. Shireen finds a music box, and opens it; a haunting melody plays prompting her to shut it. A woman's voice calls out, asking if her father has come back. Bill and Shireen believe this is the voice of the Landlord's daughter, whom says she hasn't had company for some time. She comes out of hiding, revealing herself to be completely made of wood. She introduces herself as Eliza. Downstairs, Harry is panicking because the house managed to somehow get Felicity when she was outside. The Doctor tells him not to be scared, as it isn't useful in their current situation. Believing something is living in the wood, the Doctor begins knocking on the wood to get a response. He gives a hard bang on a cupboard and out pops an insect; he speculates this could be an insect no-one on Earth has seen before, or it could be alien, a wood nympth, or a dryad possibly. The Doctor tells Harry to get a box so he can examine it. However, things get worse when a whole swarm exits the wood and backs them into a corner. The Doctor pulls Harry into the cupboard, revealing that it's a lift.

The lift takes them down to the basement, where the Doctor and Harry discover the possessions of past groups of six that the Landlord lured to the house. Each group of boxes has a contract, and each goes back at least 20 years; the contracts are from the 30s, 50s, 70s, 90s and soon the 10s, when everyone that just moved in is eaten by the house. They head outside of the room, where the Landlord meets them.

The Doctor guesses the Landlord's daughter was dying, so he used the insects to keep her alive, but the cost was to feed them six humans every 20 years. The Landlord tells the Doctor that even though an older being (as the Doctor appears to be) will have less matter and energy, the insects will take what they can. Harry tries running upstairs, but has his foot trapped and is dissolved by the insects. The Doctor states that he is a doctor, and can help the Landlord with his daughter's ailment if it's not too late. In the tower, Eliza tries reaching out to shake Shireen's hand. However, Shireen backs away in fear. She asks what's the matter. Shireen tries to cover her fear, but is soon consumed by the insects; her energy is then absorbed by the daughter. Moments later, the Doctor is lead into the room by the Landlord, who explains that he has brought a doctor to help her. Bill explains Shireen was taken, to which the Doctor explains was the case with Felicity and Harry.

The Doctor examines the daughter, coming to the conclusion that the Landlord brought the odd insects to her when she was sick to amuse her. However, the insects respond to music and awaken, such as the sound of her music box; when he checked on her the next morning, he found her wooden transformation was beginning, but her illness was cured. Bill then notes the oddity of it; why would a father spend time in the garden?

Realizing what Bill has, the Doctor remembers that humans don't live long, and if the father preserved his daughter 70 years ago, he shouldn't have been alive now as he didn't share in this immortality. Eliza becomes confused, as the Doctor explains that her memories have decayed due to the isolation and passage of time. The Landlord is actually her son, who did whatever he could to keep his mother alive. Prompted by the Doctor, Eliza realizes that her son has committed atrocities through his life just to keep her alive, in this inhuman state. She asks her son to let her die, but he refuses; taking command of the insects, Eliza thanks the Doctor for helping and has the insects devour her and the Landlord.

Without Eliza to act as the linchpin, the house begins crumbling. However, as a bonus, and the recent victims are revived and released. Everyone runs outside, just in time to watch the house crumble.

Cast

 * The Doctor - Peter Capaldi
 * Bill - Pearl Mackie
 * Nardole - Matt Lucas
 * The Landlord - David Suchet
 * Eliza - Mariah Gale
 * Shireen - Mandeep Dhillon
 * Felicity - Alice Hewkin
 * Paul - Ben Presley
 * Harry - Colin Ryan
 * Pavel - Bart Suakvek
 * Estate Agent - Sam Benjamin
 * Young Landlord - Tate Pitchie-Cooper

Culture

 * Bill makes reference to Indiana Jones.
 * Shireen says "I'm a celebrity, get me out of here", a reference to the reality TV series. She also refers to the building as a "freaky Scooby Doo house".
 * Paul says that a freshers' party is being held in the park.
 * Fireworks are used at the party.

Music

 * The figure behind the Vault can play the piano.
 * Pavel has a vinyl record, DVD players and speakers.
 * Bill has a whole playlist on Spotify with Little Mix on her phone. The playlist includes the song Black Magic.
 * One of the tenants from 1977 owned the David Bowie album Heroes.
 * Pavel has Bach: Sonata #1 by Itzhak Perlman playing in G Minor for Solo Violin, BWV 1001 - 1. Adagio.
 * The figure behind the Vault plays Für Elise by Beethoven and Pop Goes The Weasel, a famous nursery rhyme, on a piano.
 * The song heard at the start when Bill and her friends are looking for a house is Weird People by Little Mix.

Locations

 * When Felicity bemoans the lack of phone reception, Shireen says she needed a landline and Felicity jokingly asks "What is this, Scotland?".
 * A house on Mill Lane, Bristol, is shown on the estate agent's computer.
 * The park is the location of a freshers' party.
 * Shireen has once been to Morocco.

Businesses

 * A shop named The Fabric Mill is seen.
 * A cement factory can be found next to one of the houses that the students check out.

Technology

 * The house has no washing machines.
 * The plugs can't take the students' phones.
 * The house has an old-fashioned television set.
 * The hob is from the 30s.
 * Pavel plays a vinyl record using a USB turntable.
 * The Doctor uses the sonic screwdriver as a light source.
 * Eliza has a music box.
 * There's a typewriter in the basement.

Science

 * The Doctor finds an oil burning heater.

Species

 * 11 Cardinal Road has skulls from gazelles hanging on the walls.
 * Paul and Shireen jokes to Felicity that the house possibly has a "doll, that's come to life" or a "massive, freaky spider", to which Bill says it's probably just a mouse, and Felicity indirectly says she has a fear of mice.
 * Bill asks if there's a cat in the house. The Landlord denies this.
 * Time Lords need to sleep after regeneration.
 * At first, the Doctor suggests that the walls could be infested with wood nymphs or tree spirits.
 * Upon discovering the Dryads the Doctor says he expected a gaseous creature or a microscopic one.
 * The Doctor calls the woodlice Dryads, though he later reverts to just calling them lice.
 * The bass player in Quincy Jones' band turned out to be a Klarj Neon Death Voc-Bot.
 * Shireen thinks the Dryads are cockroaches.
 * The Doctor mentions flies.

Foods and beverages

 * The house has a picture of a bowl of pears.
 * There's a book on Farmhouse Cooking in the kitchen.
 * The students eat Chinese. The Doctor loves Chinese.
 * The Doctor (noisily) eats a krupuk.
 * The Doctor brought Mexican food for himself and the prisoner in the Vault.

People

 * Bill has a teddy bear.
 * Harry's grandfather and his boyfriend once got arrested for trying to steal a bit of the Great Wall of China.
 * Bill hangs up a photo of her mum.
 * Asking the Landlord who is the Prime Minister, the Doctor lists Margaret Thatcher, Harriet Jones, Harold Wilson and Anthony Eden as candidates. (This was a test to see if he was up on current events; an alien or time travelers would likely know the wrong one.)
 * The Landlord has a tuning fork.
 * The Doctor calls Harry "Simon" and Felicity "Florence".
 * The Doctor once sat in on a recording session for Quincy Jones when the bass player (who couldn't play anyway) was revealed to be a Klarj Neon Death Voc-Bot.
 * Felicity is Musophobic and Claustrophobic.
 * Felicity tried to call the police.
 * Shireen wanted to call an ambulance.
 * A tenancy agreement from 2 September 1997 was signed by Jake Christie, Annie Wren, Jonathan Frost, Sarah Tiller, Mark Hopethorne and Carl Richards. There is a further agreement from April and signed in May 1977 and one from 1957.

Organisations

 * Bill and her friends go to Redcliffe Lettings to find a new house to live in.
 * Redcliffe Lettings' phone number is 01174 960313.

The Doctor

 * The Doctor offhandedly mentions regeneration to Bill; he avoids elaborating on it.
 * The Doctor still can't tell people's ages.
 * He shares stories with the Vault's prisoner, only if they're gruesome enough.

TARDIS

 * Bill suggests the Doctor make the TARDIS a removal service.

Story notes

 * The read-through for Knock Knock took place on 18 July 2016, and filming took place in August.
 * David Suchet said in The Fan Show: The Aftershow that he used a real life experience of being covered in woodlice for the scene where the Dryads come crawling all over the Landlord.
 * In an interview for Doctor Who Magazine #512, writer Mike Bartlett indicated that Harry was intended to be the grandson of Fourth Doctor companion Harry Sullivan, but the reference was cut. A possible remnant of this has Harry recognising the Doctor's name and calling him a "legend", despite the episode establishing that Bill is not yet closely acquainted with her new flatmates; another is the fact that Harry is partnered up with the Doctor for part of the episode. There is also a dialogue reference made to Harry's grandfather and his boyfriend stealing a piece of the Great Wall of China, however it is not clear whether this refers to Harry Sullivan or another grandparent.
 * "Weird People" by Little Mix is playing extra-diegetically in the scenes where Bill and her friends are looking for a new house.
 * Shireen refers to 11 Cardinal Road as "a freaky Scooby Doo house". The episode was partly filmed on location on the same property used for Wester Drumlins in TV: Blink - in which a character also referred to the place as "Scooby Doo's House".
 * Not really noticed by everyone, but everything that Bill and her friends brought to that house either ended up buried or destroyed when it fell apart.

Ratings

 * 4.32m (UK overnight figures)
 * 5.73m (UK final)

Filming locations

 * Fields Park Road, Newport, South Wales

Production errors
to be added

Continuity

 * The Doctor mentions Prime Minister Harriet Jones, who ascended after aiding his ninth incarnation in defeating the Slitheen. (TV: Aliens of London/World War Three) His tenth incarnation, however, would set in motion her deposition after she ordered the destruction of the retreating Sycorax. (TV: The Christmas Invasion) She would help save the world one final time against the Daleks. (TV: The Stolen Earth)
 * The TARDIS materialises around Bill's possessions. It had done so previously around passengers. (TV: The Parting of the Ways, Blink, The Runaway Bride, Dinosaurs on a Spaceship, Hell Bent)
 * The Doctor mentions that he ran away from his people. (TV: The Name of the Doctor)
 * The Doctor says he loves Chinese. (TV: The Power of Three)
 * Bill says there are bits of her life that the Doctor is not in. Amy Pond and Rory Williams used to have a double-life, (TV: The Power of Three) and so did Clara Oswald. (TV: The Day of the Doctor)
 * When Bill says they should get the Doctor, Shireen asks if he's gonna give a lecture. (TV: The Pilot)
 * The Doctor remarks on the Time Lords' dress sense, having done so earlier in his life. (TV: Time Crash, Journey to the Centre of the TARDIS, Nightmare in Silver, Hell Bent) He makes note of the high collars (as seen in TV: The Deadly Assassin, et al).
 * The Doctor reveals he's a Time Lord. (TV: The War Games et al., Doctor Who, The End of the World et al.) Upon learning this, Bill scoffs at the Doctor being part of the aristocracy (TV: The Caretaker).
 * Regeneration is mentioned. (TV: The Tenth Planet/The Power of the Daleks, The War Games, Planet of the Spiders/Robot, Logopolis/Castrovalva, Destiny of the Daleks, The Caves of Androzani, Time and the Rani, Doctor Who, The Night of the Doctor, The Day of the Doctor, The Parting of the Ways, Utopia, The Stolen Earth/Journey's End, The End of Time, Day of the Moon, Let's Kill Hitler, The Time of the Doctor, Hell Bent) However, the Doctor glosses over the topic, similar to how his tenth incarnation did such with Martha Jones in regards to his race. (TV: Gridlock)
 * The Doctor had previously faced creatures who absorbed people into walls. (TV: Flatline)
 * Bill introduces the Doctor as her grandfather. The Doctor once travelled with his granddaughter Susan Foreman, who called him grandfather. (TV: An Unearthly Child - The Dalek Invasion of Earth, The Five Doctors)
 * The Doctor takes offence at being described as Bill's grandfather, suggesting father be more accurate given his appearance. (TV: The Caretaker)
 * Bill's sexuality is mentioned as she informs Paul, after he makes romantic overtures, that he isn't her type and she prefers girls. (TV: The Pilot)
 * Bill puts a picture of her mother, which was taken by the Doctor, on the wall. (TV: The Pilot)
 * One of the flat mates theorise dolls could be creeping around upstairs. The Doctor encountered a house of dolls in his eleventh incarnation. (TV: Night Terrors)
 * The Doctor uses the sonic screwdriver as a light source. (TV: Thin Ice)
 * The Doctor has met people made of wood before. (TV: The End of the World, The Doctor, the Widow and the Wardrobe)
 * The Vault is tended to by Nardole once more, the Doctor revealing a piano is inside. (TV: The Pilot, Thin Ice)
 * In an attempt to convince herself that there's nothing strange about the house, Bill remarks that "There's no living puddles or weird robots, big fish..." (TV: The Pilot, Smile, Thin Ice)
 * The Doctor claims sleep is for tortoises, (TV: The Talons of Weng-Chiang) as he doesn't sleep much himself, (TV: Good Night) usually only after regeneration (TV: Spearhead from Space, Robot, Castrovalva, Time and the Rani, The Christmas Invasion, Deep Breath) or after a big lunch. (TV: The Two Doctors)
 * The Doctor refuses to "high-five" Harry. (TV: Time Crash, Under the Lake)
 * Nardole says the prisoner has gotten a little restive lately. (TV: Thin Ice)

DVD releases
to be added

Blu-ray releases
to be added

Digital releases
to be added