by Hal Erickson
synopsis
In the conclusion of the four-part story "Logopolis," the Master (Anthony Ainley) is revealed to be the cause of the breakdown of the universe's entire structure. Caught in his own trap, the Master must rely upon his old enemy, the Doctor (Tom Baker), for his survival -- thereby creating one of the uneasiest alliances since the days of WWII. As the episode rushes to a close, the Doctor undergoes yet another of his periodic regenerations, obliging the series' fans to bid farewell to star Tom Baker after seven years' worth of episodes. Written by Christopher H. Bidmead, "Logopolis, Episode 4" originally aired on March 21, 1981, as the final episode of Doctor Who's 18th season.
