This is the first time the Doctor uses a sonic screwdriver.
All six episodes of this serial were wiped by the BBC. However, some short clips have survived due to the Australian censor.
The working title for this story was The Colony of Devils. This was changed, as the BBC wouldn't allow the use of the word 'devil' in a family programme.
In October 27, 2019, it was announced at the MCM Comic Con in London that this serial will be released in an animated form, which has been previously done with the missing episode The Tenth Planet: Episode 4 (1966) and the lost serials Doctor Who: The Power of the Daleks (2016), The Macra Terror: Episode 1 (1967) and The Faceless Ones: Episode 1 (1967).
Initially, the sonic screwdriver was just a regular screwdriver, until production assistant Michael E. Briant suggested that the Doctor should his own version that uses sonic waves. Patrick Troughton went to the Visual Effects department and picked a penlight, which he thought was an ideal prop for it. Unfortunately, on the first day of shooting, he accidentally dropped the penlight into the pipe. A safety whistle from Deborah Watling's life's preserver outfit was eventually used as a replacement.