This episode underran by four minutes. As a result, material involving Peri being taken to the Morlox cave was added. Eric Saward also extended the two TARDIS scenes.
The script gave an explanation for the destruction of the Bandril (originally "Gurdel") missile - that the bendalypse was neutralised via contact with the TARDIS's time field - to replace it only with The Doctor's vague assurance that he will explain it to Peri later (and off-screen).
The original script had the Borad reject his earlier inclination of mating with Peri because he can now make as many clones of himself as he desires.
During the 'gunfight', a piece of the wall is damaged, exposing a likeness of the Jon Pertwee version of The Doctor.
This episode was watched by 7.4 million viewers on its original transmission.