Serial: EEE  Episode Nos. 279, 280, 281, and 282..  Title: Terror of the Autons

The last surviving Nestene energy unit is stolen by the Master, a rival Time Lord and the Doctor's greatest adversary.
He acts as the Nestene's new agent on Earth to prepare the way for a second invasion attempt, once again using the
killer Auton plastic robots as well as other devices of his own design.  The question is, can the Doctor and UNIT track
him down and stop his plans in time to save the world?

This story sees the debut of the Doctor's archenemy the Master, played by Roger Delgago.  It also marks the debut of
Katy Manning as Jo Grant and Richard Franklin as Captain Yates.

starring Jon Pertwee as Doctor Who, Roger Delgado as the Master, Nicholas Courtney as Brigadier Lethbridge-Stewart, Katy Manning as Jo Grant, Richard Franklin as Captain Yates, and John Levene as Sergeant Benton.. Written by Robert Holmes, Produced and Directed by Barry Letts..

Originally transmitted from 2 January 1971 to 23 January 1971 on BBC1.