In the conclusion of the pivotal four-part story "The Caves of Androzani," the Doctor (Peter Davison) risks his own life to save his travelling companion, Peri (Nicola Bryant), from the fatal side effects of the "miracle" drug Spectrox. In so doing, the Doctor collapses -- and as he lies in helpless dormancy, a bizarre but familiar metamorphosis takes place. Peter Davison makes his farewell appearance in this episode, which features an unbilled cameo appearance by Colin Baker. Originally telecast on March 16, 1984, "The Caves of Androzani, Episode 4" was written by Robert Holmes. ~ Hal Erickson, Rovi