Working titles for this story included
The Trap and
The Space Trap. Holmes had originally submitted
The Trap to the BBC as a stand-alone science-fiction serial in 1965. Head of Serials
Shaun Sutton rejected the serial as being not the kind of thing the BBC was interested in making at the time, but suggested the writer pitch it to the
Doctor Who production office as an idea for that series. Holmes did so, and although story editor
Donald Tosh was interested, the scripts went no further at the time. Some years later, assistant script editor
Terrance Dicks found the story in the production office files when clearing a backlog, and decided to develop it with Holmes as a personal project, in case other scripts fell through. When the latter event occurred (Dick Sharples script
Prison in Space, a comedic dystopian tale where females rule with
dollybird guards, proved unworkable), Dicks was able to present the serial to his superiors as a ready production. Director
David Maloney agreed the serial was viable, and it went before the cameras very quickly as an emergency replacement. Robert La'Bassiere is actually a pseudonym for Robert Grant, who requested that he be credited under this name for his appearance as one of the Krotons. Scenes set on the planet's surface were filmed at the Tank Quarry and West of England Quarry on the
Malvern Hills.
Cast notes One of the guest actors for The Krotons is
Philip Madoc, who appeared in a different role later in the season in
The War Games (1969) as well as in other roles with
Tom Baker's
Fourth Doctor. The actor James Cairncross, who plays Beta, previously appeared as Lemaitre in
The Reign of Terror with
William Hartnell's First Doctor. ==Broadcast and reception==