The Doctor, Jamie and Zoe only appear in pre-filmed inserts, as Patrick Troughton, Frazer Hines and Wendy Padbury were filming The War Games. A common criticism of this serial is how little the regulars affect the main plot.
This episode was wiped by the BBC and no copy of it is known to exist. It is chronologically the last episode of Doctor Who (1963) that does not exist either on film or videotape.
This episode was watched by 5.3 million viewers on its original transmission.