Several men are looking at photographic slides. They are trying to work out the whereabouts of a 'Dr. Seltzman' but seem unable to locate him. In the Village, the new No.2 welcomes the "Colonel" who has just arrived. He is briefed on Dr. Seltzman, and on the 'mind-swapping machine' which he invented. The Village are in possession of some of Selzman's technology but it only works one way - they can swap the minds of two persons, but not reverse the process. They need to locate Selzman to extract the rest of the information they need. It's known that No. 6 was a close friend of Selzman and could probably find him, so the plan is to use the mind-swap technique to swap minds between No.6 and the Colonel. No. 6 (with his psyche now trapped inside the Colonel's body) would be motivated into finding Selzman in order to get the process reversed.

No.6 awakens in his London apartment, in the colonel's body, but without recollection of the experiment. Janet, his erstwhile fiance enters the scene and he learns that he has been 'away' for over a year. Janet, of course, sees only the Colonel, as does her father, Sir Charles Portland, who also just happens to be No. 6's former boss. No. 6 is unable to convince anyone of his true identity and realises he has to track down Seltzman. At Janet's birthday party, No.6 asks her to find a slip of paper 'he' gave her a year ago. This is actually a sales slip for photographs that he later collects. Back at his apartment, he superimposes the slides in a certain order and discovers the name of an Austrian town, Kandersfeld. Once there, he easily finds Seltzman who is now the local barber. Once sure about his visitor's identity, the doctor agrees to try and reverse the process. After a fight with Portland's henchman, who has followed No. 6, a Village operative arrives and gasses them all.

They are brought back to the Village where Selzman agrees to reverse the process on the understanding that he works alone. After a lot of flashing of lights and spinning of gadgetry, the process appears to have worked. The Colonel gets up and promply leaves after a short interchange with No. 2. However, Selzman recovers a little later and is obviously not himself anymore. He has tricked the Village by transferring his psyche to the Colonel's body and escaped in it, leaving the Colonel trapped in the Selzman body. Only No. 6 has been restored, and he confirms that Selzman is now free to continue his experiments elsewhere.