This episode was wiped by the BBC. It is still missing from the BBC archives and is listed as one of the top ten missing British television programs, alongside the BBC news studio commentary from the Apollo 11 mission. However, footage of the regeneration from William Hartnell to Patrick Troughton does exist due to a clip used in Blue Peter (1958).
In the original script, The First Doctor's last words were, "No. No, I simply will not give in".
This episode was the last to feature William Hartnell as The First Doctor and also features the first re-generation.
The setting of this episode was returned to in 2017's Doctor Who (2005) Christmas special, Twice Upon a Time, over 51 years after its original airing.
This episode takes place in Antarctica in December 1986.