Beryl Reid was Cast by John Nathan-Turner. The rest of the cast was chosen by Peter Grimwade.
The regular cast and Eric Saward thought Beryl Reid was miscast.
Patricia Phoenix was a possible for Captain Briggs.
Although the Cybermen refer to the events of "Tomb of the Cybermen" (1967) during the flashback sequence, the story was not extant in the archives at the time, so a clip from "Doctor Who: The Wheel in Space: Episode 6 (#5.40)" (1968) was used instead.