The original script had newly-regenerated Doctor wondering where he'd left Susan.
All six episodes of this serial were wiped by the BBC.
Only the audio track and some stills survived from this serial, which had been recorded by fans. Those served as a basis for an animated reconstruction, which was released in 2016.
As Patrick Troughton was fond of practical jokes, Michael Craze and Anneke Wills once greeted him wearing t-shirts reading "Come back Bill Hartnell - all is forgiven". Apparently, Patrick Troughton believed them and was upset by this.