In the conclusion of the four-part story "Earthshock," the leader of the Cybermen intends to destroy the earth by forcing the crash-landing of a huge, heavily armed space vessel. The Doctor (Peter Davison), Tegan (Janet Fielding), and Nyssa (Sarah Sutton), all locked in the TARDIS, are unable to prevent this catastrophe. It is up to Adric (Matthew Waterhouse) to save the day -- and without giving away the ending, it should be noted that this episode represented Adric's final Doctor Who appearance, at least until a surprise guest-shot in the 21st season adventure "The Curse of Androzani." Written by Eric Saward, "Earthshock, Episode 4" originally aired on March 16, 1982. ~ Hal Erickson, Rovi