Writing In late 1969, script editor Terrance Dicks contacted new writing duo Bob Baker and Dave Martin after reading a draft script they had sent around the BBC for another production, ''A Man's Life
. After offering the duo a seven-part story in November 1969 for Doctor Who''s
eighth season, Baker and Martin submitted some various storylines they had. Despite the storylines not being suitable for a serial, Dicks commissioned an opening episode from them on 1 December, but as part of a six-parter, rather than a seven-parter. The original storyline for the serial was set in central
London, with
Battersea Power Station taking the place of Nuton Power Complex. However, the serial would have been too expensive to make on the budget available, and Dicks promptly told the writing pair to scale down the story.
Filming Location shooting was planned to take place over five days in early 1971, starting on 4 January. Filming would take place in various locations around Kent, mainly
Dungeness. During the location shooting of the scenes with the tramp, an overnight snow storm necessitated the creation of a line of dialogue in the programme to explain that the variations of weather from shot to shot in these scenes (filmed on various days but supposedly taking place within minutes of each other) are "freak weather conditions" as a result of Axos' arrival. In some of the car interior scenes the
colour-separation overlay (CSO) backgrounds were omitted, leaving the blue screen behind the characters. As Paul Vanezis of the
Doctor Who Restoration Team explained in an interview, "they didn't put a background in there [as] it wasn't lit properly. There wasn't enough blue in it to key it, or yellow or green or whatever it was. It was shot wrong. It shouldn't have been shot in the studio and it shouldn't have been shot on xchrome. These days with modern technology you could easily key it... easily, but it wouldn't look right." The story includes interior scenes inside the TARDIS for the first time in the Pertwee era of the show. The configuration of the TARDIS set-up is unique for this adventure. The TARDIS monitor appears to be a circular screen embedded in one of the 'roundels' in the console room wall, rather than the traditional rectangular screen (this feature is seen again once, a year later, on the unique set built for
The Time Monster). The doors of the console room do not open directly into the exterior as in all other adventures; instead they open into a corridor that features the 'roundel' motif. When the TARDIS interior reappears, in the next production (
Colony in Space), both these features have been eliminated.
Cast notes Bernard Holley had been last seen in
The Tomb of the Cybermen (1967). He reprised his role of Axos in the 2011 audio play
The Feast of Axos. Peter Bathurst had previously played Hensell in
The Power of the Daleks (1966). Tim Pigott-Smith would later play Marco in
The Masque of Mandragora (1976). ==Broadcast and reception==