Written by David Whitaker
From a Story by Kit Pedler
Directed by Tristan DeVere Cole
The TARDIS materializes on board a spaceship, the Silver Carrier, where the Doctor and Jamie are attacked by a maintenance Robot. Jamie manages to contact a nearby space station known as the Wheel and they are rescued. Though viewed with suspicion by many of the crew, the Doctor and Jamie befriend Zoe Heriot, a young prodigy with total recall and broad scientific knowledge, as well as a healthy ego.
Meanwhile, the Silver Carrier discharges Cybermats, which travel to and enter the station. These pave the way for the penetration of the station by Cybermen, who intend to use its direct radio link with Earth as a beacon for their invasion fleet.
The Doctor sends Jamie and Zoe over to the Silver Carrier to fetch the TARDIS's vector generator rod. Meanwhile he manages to free the Wheel's crew from the Cybermen's hypnotic control and to destroy all the Cybermen on the station.
When Jamie and Zoe return, he installs the rod in the station's X-ray laser, making it powerful enough to destroy the Cyber-fleet. Zoe joins Jamie and the Doctor in their travels.