Bill Potts (Pearl Mackie) and five students, looking for cheap lodging, rent a large mansion for peanuts. Bill talks the Doctor (Peter Capaldi) into helping her move. At first, she is troubled by the Doctor being a little too friendly with her buddies, and then she is disturbed by the strange noises in the house. The landlord (David Suchet) turns up, and he is decidedly strange. Highly suspicious, the Doctor quizzes him on Earth politics and he evades the questions. That night, there is a loud knocking in the walls, and Bill’s friends begin to disappear. All the exits from the house are sealed tight and no-one can leave. Bill and her friend Shireen (Mandeep Dhillon) see Pavel (Bart Suavek) half absorbed into the wall, and the landlord arrives. He strikes a tuning fork and Pavel disappears completely. The Doctor discovers the woodwork infested with insectoid Dryads, which consume the victims. It seems every twenty years a new set of students are brought in to feed the Dryads. The landlord admits that he needs the Dryads to keep his daughter Eliza alive in the tower.
The Doctor and Bill ascend the tower and find Eliza (Mariah Gale) entirely made of wood. The Doctor discovers that the landlord is actually Eliza’s son. As a child, he brought his mother some interesting bugs he found. When the creatures heard the sound of a music box, they began to turn Eliza into wood to protect her from her terminal illness. He has been providing students as food for Dryads ever since. Eliza is horrified to learn that she has lived so long at such a cost. Eliza hugs the landlord, and the Dryads consume them both.
Bill’s friends are restored, and they all escape the house as it collapses on itself, as haunted houses tend to do in movies. Back at the University, the Doctor takes over the watch of the vault from Nardole (Matt Lucas). Piano music is heard from within, and the Doctor enters to have dinner with the prisoner inside.
The Fields House in Newport was used as the haunted mansion. David Suchet was disturbed to learn that he and his family had rented the place the previous Christmas. David Suchet has appeared in many British movies and programmes, including Oppenheimer, Greystoke, Freud, Moses, Dracula, and His Dark Materials, but is best-known, of course, for playing Hercule Poirot on TV for 25 years. The house was used in the Blink episode as well. Peter Capaldi and David Suchet appeared together in an episode of Poirot. Suchet is quite brilliant here, creepy and yet somehow sympathetic and the Doctor and Bill are wonderful together.