Because of illness, William Hartnell was unable to work on this part. His lines were given to Anneke Wills, Michael Craze and David Dodimead.
This episode takes place in Antarctica in December 1986.
Because of rewrites The Newsreader's appearance in this part was cut.
The Doctor spends this episode "recuperating," after the script was re-written to accommodate William Hartnell's absence.
This episode was watched by 7.6 million viewers on its original transmission.