The only complete serial in Doctor Who to only feature the regular cast, with no guest actors appearing.
Producer Verity Lambert had to write a letter of apology after the children's department made it known they felt it was an unwise decision to show Susan acting out violently with a pair of scissors.
This is the first Doctor Who Story to have not needed an episode to be re-shot or remade.
The director originally assigned to this serial was Paddy Russell, one of the first female directors at the BBC. Russell was not available for the studio dates, however, and Doctor Who's associate producer, Mervyn Pinfield, was suggested as her replacement.
This episode was watched by 10.4 million viewers on its original transmission.