In the third episode of the four-part story "Earthshock," the Doctor (Peter Davison) has materialized on earth in the 26th century, where a huge super-bomb of alien origin is sequestered in a cave, guarded by a pair of murderous robots. To his chagrin, the Doctor learns that the bomb is the handiwork of his old nemeses, the Cybermen, who are (again) scheming to destroy the world -- beginning with a conference where the delegates are discussing the destruction of the Cybermen. Written by Eric Saward, "Earthshock, Episode 3" originally aired on March 15, 1982. ~ Hal Erickson, All Movie Guide