This episode was Roger Delgado's final appearance as The Master. Due to time constraints in the studio his final scripted scene was not taped. Delgado was due to reappear as The Master in Series 11, but was killed in a car accident while in Turkey for a film called "Bell of Tibet.".
Jon Pertwee was sentimental towards this episode, stating that he loved the Cavalcade of monsters (The story featured 7 different monsters) and because it was the last time he was able to work with his dear friend Roger Delgardo before the latter's untimely death.
One of Peter Capaldi's favourite Doctor Who (1963) episodes.
The final sequence in the Master's headquarters was intended to contain the giant Ogron-eating monster, but director Paul Bernard did not like the costume and omitted it, leaving the scene with just frightened Ogrons running away from something unseen. Barry Letts and Terrance Dicks felt the sequence lacked impact and a new ending was filmed in the TARDIS as part of the first production block of the following story, Planet of the Daleks.
This episode was watched by 8.9 million viewers on its original transmission.