Surely a top ten entry on anyone's list of favorites, this episode has two enemy spies swapping identities with Steed and Mrs. Peel so as to bump off the Avengers network from the inside. Philip Levene, along with Brian Clemens, was clearly among the series' best writers (and here puts in a cameo as Daffodil), and this ingenious script allows Sir Patrick and Dame Diana to indulge in all the delightful carnage they wouldn't ordinarily do (Mrs. Peel chewing gum, Steed planting a big wet one on Emma's luscious lips!) Often overlooked is the excellent work from top billed Patricia Haines (previously seen in "The Nutshell" and "The Master Minds") and Freddie Jones (Hammer stalwart of "Frankenstein Must Be Destroyed" and "The Satanic Rites of Dracula"), the only time two different actors enacted the roles of The Avengers, having no success in convincing their superiors of what has transpired (Question-"Do you take me for a perfect idiot?" Answer-"No one's perfect!") Another favorite line concerns Steed noting that Basil bites off the ends of his cigars, remarking that such a man is capable of anything! (longtime viewers remember that Steed himself did just that in previous seasons). Things really start to heat up once the villains realize that they much prefer their new bodies over the old, ordering Steed and Mrs. Peel to be shot on sight! This was the only time during the Emma Peel era that we see one of Steed's superiors, here called Major "B" (Campbell Singer, previously seen in "Six Hands Across a Table"), running 'a bouquet of agents,' somewhat similar to Patrick Newell's Mother, who would soon arrive on the scene. Sit back and enjoy the two stars having the time of their lives, and let the narrator be confused for a change. Peter Reynolds previously did "Double Danger," Malcolm Taylor had done "Mission to Montreal," while Arnold Diamond (playing the inventor of the transmigration machine) returned for the excellent "Fog," but Patricia Haines ("The Night Caller," "The Virgin Witch"), the lovely former wife of actor Michael Caine, was making her last appearance on the show (her tragic death in 1977 at 45 was due to cancer). This gem was the only episode to be directed by veteran John Llewellyn Moxey, who did the classic "City of the Dead" (1960), before emigrating to Hollywood to become even more prolific in TV movies like 1971's "The Night Stalker," which inspired the cult series that followed in 1974.