Patrick McGoohan was not available for this episode since he was finishing up his role on the movie Ice Station Zebra (1968). In this episode his mind was transferred to another body and another actor played Number 6.
This is the only Prisoner episode to begin with a pre-credits teaser sequence (not counting the recap which opens "Fall Out"). It shows several men, including one who will be identified later in the episode as the former superior of Number 6, trying to find clues to the whereabouts of Professor Seltzman in a group of seemingly innocuous photographic slides. According to "The Prisoner" by Robert Fairclough, had the series been renewed for a second season, the format would have followed that presented in this episode, with Number 6 being sent out on missions on behalf of The Village.
In the scene where Seltzman produces the letter that Number 6 had sent him previously, Seltzman's Scottish address starts "Portmeirion road", which is the name of the actual hotel in Wales where "The Prisoner"'s exterior scenes were filmed.
This is also the only The Prisoner (1967) episode to show Number 6 kissing a woman (although he is in another man's body, hence the scene did not involve the devout Catholic and very moral Patrick McGoohan). It is also the only time that it is mentioned that No 6 has a fiancée: Janet Portland, his boss' daughter.
Number Six's internal monologue while in the Colonel's body and the final scene in which his mind is returned to his own body were the only sequences which Patrick McGoohan recorded for this episode. All of Number Six's other appearances (in his own body) were either footage from the opening sequence, Arrival (1967), Free for All (1967) and the not yet broadcast Once Upon a Time (1968) or involved the use of a stand-in.