In the conclusion of the four-part story "The Macra Terror," the Doctor (Patrick Troughton) escapes the Macra salt mines in hopes of rescuing the earth colonists from being used as the principal component in a gaseous mixture. Things come to a head when the Doctor finally comes face to face with the Controller (Graham Leaman), who may be responsible for the dirty work perpetrated by the crablike Macra. Written by Ian Stuart Black, "The Macra Terror, Episode 4" first aired on April 1, 1967. This episode apparently no longer exists. ~ Hal Erickson, Rovi