19 April 1975
Jeremy Wilkin (Kellman), Ronald Leigh-Hunt (Commander Stevenson), William Marlowe (Lester), Alec Wallis (Warner), David Collings (Vorus), Michael Wisher (Magrik), Christopher Robbie (Cyberleader), Kevin Stoney (Tyrum), Brian Grellis (Sheprah), Melville Jones (First Cyberman).
Following on from Genesis of the Daleks, The Doctor, Harry and Sarah use theTime Ring, spinning their way through time and space back to Space Station Nerva. They land back in the control room they left when they last beamed down to Earth, but Sarah notices the TARDIS is not there. The Doctor tells Sarah that the time ship is drifting back in time towards them and they just need to wait for her to catch up. A door slides open, revealing a dead body, and many more beyond, littering the outer ring of the station.
In a communications room, crewman Warner warns off an approaching spaceship away from Nerva Beacon, which is under quarantine due to a plague. Professor Kellman, a planetary surveyor, asks Commander Stevenson how long they can run a 50-man station with three men, but the other young officer, Lester, thinks they can continue to manage. Nerva is on a 30-year assignment to warn ships away from Voga, the new asteroid it is orbiting, until its presence is updated on all the starcharts of inbound ships.