This entertaining episode completed during the fourth season of The Avengers television series, shot in black and white, was originally aired in the United Kingdom 18 December 1965, and during the subsequent May was seen upon TV screens in the United States. The title is allusive to John Steed (Patrick Macnee)'s evidently having a doppelgänger, this exact copy being particularly perplexing to Steed's Avenger partner, Mrs. Emma Peel (Diana Rigg), as well as to those viewers who will immediately wonder at what may have brought about the appearance of his ostensible duplicate. Steed has been designated by his governmental office as chief of security for a defense conference to be held at a Cold War rival nation's embassy in London (actually the Edge Grove prep school in Hertfordshire). It has been determined that a mysterious secret agent, Colonel Psev, along with four aides, will be present at the upcoming convention, and since Psev has not been visually recognizable to the West, Steed is specifically charged with the ascertainment of the Colonel's true identity. The mentioned quartet of the enigmatic Psev's deputies have anteceded the Colonel to the embassy site and, in concert with their country's ambassador Brodny (Warren Mitchell), have formulated a thoroughgoing espionage exercise there that will audit the conference. By an astounding bit of luck, the group has located an exact replica of Steed, a clothing model named Gordon Webster whose complete lack of principles makes him ideal for the purposes of the spies who have come from behind the Iron Curtain. He even gulls Mrs. Peel. When she informs Steed of the existence of his duplicate, he retorts: "If I had a twin, I'm sure mother would have mentioned it." For those interested in the technological content of Avengers series episodes, there are recording devices (bugs) of several sorts, and also a remote controlled model aeroplane (Lancaster bomber), and a model submarine, the latter filmed at Tyke's Water Lake, Elstree, also in Hertfordshire. The scenario is overly complex, and may thereby cause some viewers to focus upon obvious breaches in logic and continuity, for what is, after all, a piece from a chain of tales that rely upon acceptance of fantasy. Nonetheless, outstanding performances (as ever) by Macnee and Rigg, in addition to a top-flight turn from Mitchell, will inspire a good many who view the film to grant it a high ranking.