A constable uses a police box on a British motorway. The box suddenly shimmers and warps and his call is cut off. He is dragged inside to his demise.
The Doctor is pacing in the TARDIS cloisters, lamenting the state of old the time machine. He tells Adric he's decided to go to Earth instead of Gallifrey.
Tegan, an air hostess, leaves her Aunt Vanessa's home to catch her flight to Brisbane.
The Doctor tells Adric he plans to find a police box on Earth. Perturbed by his encounter with the Master, he plans to measure the box, take the numbers to Logopolis and have them use block transfer computation to repair the chameleon circuit and allow the TARDIS to change its shape. As they talk, the TARDIS cloister bell begins to ring an alarm.
Tegan develops a flat tire near the motorway police box. As she repairs it, the TARDIS materializes nearby. The Doctor hops the TARDIS to materialize directly around the other police box, which appears inside the console room.
Tegan and Vanessa try to repair the tire. They are watched by a strange white figure. Tegan finds that the spare tire is flat.
As the Doctor explains Logopolis to Adric, the TARDIS powers down — the effect of a gravity bubble. The Doctor steps out onto the motorway and glances at Tegan and Vanessa. But his attention is immediately drawn to the Watcher, who stares back.
Adric picks the lock of the police box. They go in and find another dimly lit console room.
Tegan sets out for the garage but stops to use the police box. As she enteres the console room, the other police box dematerializes. She calls out but is answered only by the cloister bell.
The Doctor and Adric continue to progress through police boxes into increasingly dim console rooms. They hear the vague echo of the cloister bell.
Vanessa follows Tegan into the TARDIS. But she is approached by a dark figure, who laughs evilly. A bright red light envelopes her.
The Doctor tells Adric they have materialized around another TARDIS. He steps through another police box but finds himself outside, with a detective inspector investigating the abandoned car. The inspector questions the Doctor and brings him to the car. The Doctor looks in and realizes the Master has escaped from Traken. Inside the car are the shrunken corpses of the constable and Vanessa…