Katie arrives for a one-night job at a gothic mansion. She is greeted by Tabitha, an aging woman who lives in the mansion with her brothers Hector and Andras. Tabitha explains that the mansion is kept permanently at three degrees below zero because of Andras's medical condition. She and Hector never leave the house, but tonight they have an appointment they cannot miss, and Katie was recommended to them by a friend from church. Katie is officially there to look after Andras, but Tabitha explains that Katie will almost certainly not see him: she is really there to look after the house. There are milk and rusks in the kitchen, which are the only things Andras can eat: he has no mouth. As she and Hector leave, Tabitha adds that Andras has a bell by his bed, but he never rings it.
Once they are gone, Katie explores the house, finding a stuffed cat. Her friend Shell arrives to see her, and finds the cat alive and mobile. Katie is increasingly disturbed and wants to leave, but Shell insists that she should stay in case Andras needs her. The bell rings, and a reluctant Katie goes upstairs to Andras's room to find out why.
Andras turns out to be an old man tied to a bed. He has a mouth as well, but is gagged, although his feet seem badly deformed. Katie removes the gag, and Andras begs to be free. Katie concludes that he is just an old man being held against his will, and starts trying to untie his bonds until Shell points out a problem: if Andras's hands were tied down, how could he ring the bell?
The bell rings again and Tabitha reappears, holding it. Hector is with her. They explain that, at the age of ten, Andras was possessed by a demon, and has been kept in the attic room ever since to contain it. Now, however, his mortal body is dying and his death will set the demon free unless a new host can be found. This is where Katie comes in: she was recommended by Shell, who is also a regular at Tabitha and Hector's church because she has the strength of will to contain the demon for another fifty years.
Katie refuses to accept this, even as Hector produces a taser. She hits him with his guitar, causing the taser to strike Tabitha, and runs downstairs. All the doors are locked, and she is cornered by Shell, who insists that she has been chosen for a great honour, before injecting her with a sedative. Katie awakes in her bra and knickers, cleave-gagged and tied to a chair in Andras's room. She watches in terror as he climbs out of bed and advances towards her.
This episode contains examples of:
- Affably Evil: Shell seems to genuinely think that Katie has been selected for a great honour and should be happier about it.
- Bound and Gagged: Both Andras and, at the end, Katie.
- Brother–Sister Team: Tabitha and Hector are a villainous example.
- Cat Scare: Several, including real cats and one stuffed cat corpse.
- Cell Phones Are Useless: They don't work at Hector and Tabitha's house.
- Cruel Twist Ending: Katie really doesn't deserve any of this.
- Demonic Possession: The intention.
- Evil Is Deathly Cold: Tabitha and Hector's mansion is constantly kept below freezing because as described in The Divine Comedy, hell is cold; so the demon within Andras needs a refrigerated environment.
- Fate Worse than Death: Spending fifty years tied to a bed in a freezing room, possessed by a demon and being fed nothing but milk and rusks is certainly this for Katie. Andras's impending death is probably the best thing ever to happen to him.
- Gothic Horror: The genre.
- Hammer Horror: The other main thing that the episode is inspired by.
- Mood Whiplash: The horrific ending is followed by the episode's choice of theme music: The Dubliners' jaunty rendition of "Lord of the Dance".
- Perky Goth: Shell. She even remains as such after The Reveal.
- Sealed Evil in a Can: Played with; Tabitha and Hector did this with Andras, but the secret is that they want it like this, rather than the usual implication of protecting others.
- White Hair, Black Heart: Both Helen McCrory and Reece Shearsmith both have gray-white hair to indicate their extreme age.
- Whole-Plot Reference: To The House of the Devil.
