The TARDIS materialises on board a spaceship, the Silver Carrier, where the Second Doctor and Jamie are attacked by a servo robot. Jamie contacts a nearby space station known as the Wheel and they are rescued. Meanwhile, the Silver Carrier discharges Cybermats, which also travel to and enter the station. These pave the way for the invasion of the station by Cybermen, who intend to use its direct radio link with Earth as a beacon for their invasion fleet.