"Doctor Who: The Invisible Enemy": While answering a mayday from a refuelling station on Saturn's largest moon, the TARDIS passes through a mysterious cloud that carries a space virus. The Doctor is soon infected and fighting for control of his mind. Leela's only hope lies on a nearby medical satellite, where she seeks help from eccentric scientist Professor Marius and his dog-shaped computer, K-9. "K9 And Company: A Girl's Best Friend": Sarah is looking forward to spending a quiet Christmas with her Aunt Lavinia in the sleepy village of Morton Harewood. But when she arrives, she finds her aunt missing, and a surprise present from an old friend waiting to be opened. Sarah and her aunt's ward, Brendan, are soon caught up in the affairs of a mysterious cult who practice the black arts, and are preparing for a human sacrifice. But Sarah has the Doctor's gift to help them - a robot dog who answers to the name of K-9.