Much like the First Doctor serial "The Massacre of St Bartholomew's Eve" (1966), this serial was influenced by the lead actor's desire to play roles other than the Doctor. Initially, it was planned that Troughton's two characters would meet more than once, but due to the technical complexity, there was eventually only the one confrontation scene, at the story's climax (utilising editing and a split-screen technique). Barry Letts planned six split-screen shots. He called for a matte box to mask half of the camera lens, having read about the technique used for old Hollywood films. The film was rewound after the first take and Troughton was then filmed in his other costume. However, after the first such shot, the camera jammed, and no more split-screen takes were filmed. Later, Letts mentioned this to Derek Martinus, director of the preceding story, who brought Letts up to date with the contemporary technology of filming normally then using an optical printer to combine the material.