Serial: TT  Episode Nos. 210, 211, 212, 213, and 214  Title: The Dominators

The pacifist people of the planet Dulkis are at grave risk from hostile aliens called Dominators and their deadly robot
servants, the Quarks.  With no defenses of their own or knowledge of how to fight, only the Doctor can prevent
their planet being turned into a giant radioactive mass....

starring Patrick Troughton as Dr. Who, Frazer Hines as Jamie, and Wendy Padbury as Zoe.. Written by Norman Ashby, Produced by Peter Bryant, Directed by Morris Barry.

Originally transmitted from 10 August 1968 to 7 September 1968 on BBC1.