On the planet Fosforon, Avon and Vila sneak into Q-Base, a Federation com-station, looking for a crystal needed to decrypt new Federation pulse-codes. In space, Zen detects a 700-year-old Earth vessel on approach to the station and Cally senses something "malignant" aboard. Blake anonymously warns the station of the ship despite objections from Jenna that he is helping the enemy. On the planet, Avon blackmails Tynus, a former associate, to help Avon steal the crystal. Tynus arranges for a diversion that will allow Avon to slip past security, but it may be a ruse. Meanwhile, the base tows the derelict back to the planet whereupon Blake teleports down to warn them in person, but he is too late as the base unwittingly releases a swift-killing alien virus.

Guest Stars: Paul Daneman (as Dr. Bellfriar), Ronald Lacey (as Tynus), Colin Farrell (as Gambril), Colin Higgins (as Tak), Morris Barry (as Wiler), Michael Gaunt (as Bax)