Sarah and K9 have joined Mike Yates' psychical investigation group. Sarah intends to do a story on their investigations of an old ballroom. She meets the members of the group and helps them set up for their investigations. While they are separated, someone approaches K9 and shuts him down.
That night they break up into groups and check the equipment. In the main hall, Peter notices that K9 isn't working and offers to fix him.
Bob and Shirley investigate the attic, which is unexpectedly locked. Mike investigates a bedroom, then a kitchen. In the kitchen, he notices that a faucet is dripping, but the water is falling up, not down. Shaun checks out the library, then hears music coming from the next room. He assumes it's a radio, but when he goes to the next room, there is no radio. The floorboards of the room bounce as if several pairs of feet were dancing on the floor. Sarah, on an upper floor, hears music below and heads off in that direction. She sees Shaun run out of a room and enters the room herself.
Mike goes to the main hall, but there is no sign of Peter or K9, and the room appears run down. His foot goes through a floorboard. When the group's patron, Count Marius Castillo, approaches him from behind, Mike turns, noticing that the room has resumed its normal appearance, and Peter and K9 are back.
Sarah enters the room with the music and finds several Victorian era couples dancing, only they are moving backwards.
Mike and the Count pull up a floorboard and find several pipes, which the Count says can conduct several types of energy. They hear a radio, and the Count sends Mike to investigate.
As Sarah approaches a radiator in the ballroom, the dancing becomes slower and slower until it practically stops, then it starts up again, this time moving forward. The people notice Sarah, and one of them screams, but as she backs up against the radiator, they all disappear. Mike joins her.
In another room, Shaun, terrified, huddles near a radiator and drinks from his flask.
In the main hall, Peter has nearly finished working on K9 when someone approaches him.
The Count joins Sarah and Mike, and they tell him about the ballroom. He heads back downstairs. They follow, but when they reach the main hall, only K9 is there. Mike pulls up another floorboard, and they find the tiny corpse of Peter.
The Count, actually the Master, confronts them and explains that this house is owned by the Doctor and is built over a time fissure. The strange phenomena that they encountered were caused by the imminent arrival of a TARDIS, and the Master intends to use the energy to cause a time ram, destroying the Doctor's TARDIS and this house. Sarah shouts for K9, who has been repaired by Peter, to shoot the Master, but the Master dodges it.
Sarah sends K9 to take care of the impending time ram, and she and Mike duel the Master with swords. The Master escapes, his plan foiled.
- Sarah mentions a UNIT reunion party where she and Mike saw Brigadier Lethbridge-Stewart.
- Brendan Richards is studying at the University of Cambridge.
- K9 destroys the Master's time vector filter.
- K9 claims that is shaped like a dog because "the human ego requires a familiar reference point to aid in adjusting to new concepts. Animal forms are comforting to the majority of humans."
- K9 runs on an electron-fusion nuclear battery.
- "The Count" drives a Mercedes.
- The Master mentions Jo Grant.
- David A. McIntee's description of Count Marius Castillo matches his description of the Master in the novel First Frontier.
- The stories in Decalog 2 have a common theme of homes owned or acquired by the Doctor. The home in this story is the house which Sarah and Mike are investigating.
- The Master mentions his encounter with Sarah in the Death Zone (TV: The Five Doctors) and his encounter with the Doctor in Atlantis. (TV: The Time Monster)
- Mike recalls plastic mannequins coming to life (TV: Terror of the Autons) and dinosaurs appearing out of nowhere. (TV: Invasion of the Dinosaurs)