In the third episode of the four-part story "The Horror of Fang Rock," the Doctor (Tom Baker) and Leela (Louise Jameson) help the keepers of the lighthouse in the English coastal village of Fang Rock fend off an invasion from space by the alien Rutans. Unfortunately, these efforts are undermined by one of the keepers, who is actually a Rutan scout in human form. Written by Terrance Dicks, "The Horror of Fang Rock, Episode 3" first aired on September 17, 1977. ~ Hal Erickson, Rovi