The complete classic serial “The Daleks’ Master Plan” consists of 12 episodes.
Broadcast on BBC1 from 13 November 1965 to 29 January 1966, it was the fourth serial of Doctor Who’s third season and starred William Hartnell as the First Doctor. Its unusually long structure allowed the story to follow the Doctor and his companions across multiple worlds while they tried to stop the Daleks from developing a devastating ultimate weapon.
The serial was preceded by “Mission to the Unknown,” a separate one-part episode that acts as a prologue. That episode is sometimes counted informally when people discuss the wider storyline, but it is not one of the twelve episodes of “The Daleks’ Master Plan” itself. The Christmas Day episode, “The Feast of Steven,” is also part of the twelve-part serial despite its deliberately comic tone.
The story was the longest Doctor Who serial until “The Trial of a Time Lord” in 1986. Seven of its twelve episodes remain missing from the BBC archives, although audio recordings survive for the complete story.