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In the fifth episode of the seven-part story "Inferno," the Doctor (Jon Pertwee) is unable to convince the fascist government of the "alternative-universe" England to halt Project Inferno, wherein the earth's core is drilled in search of new energy sources. Just as the Doctor has feared, the project sets in motion the destruction of the earth. But though the fate of the planet is inexorable, there may still be hope for mankind -- if the Doctor acts quickly enough. Written by Don Houghton, "Inferno, Episode 5" first aired on June 6, 1970.