This fast-moving episode, the second from the concluding (seventh) series of THE AVENGERS, was prepared in September 1968 for its United States viewing, and during the following month was first seen in the United Kingdom. It is The Avengers directing debut of John Hough and also marks the second appearance of Tara King (Linda Thorson) as successor to Mrs. Peel (Diana Rigg), the companion of John Steed (Patrick Macnee) in the very popular set wherein the secret agent duo face often outlandish challenges while protecting the Crown. This pleasurable sequence, one of five that Tony Williamson wrote after Tara became an Avenger, depicts a threat pointed against the M.O.T.C. (Ministry Of Top-Secret Codes), and is distinguished by a good deal of witty dialogue, in addition to a clever storyline that features Tara working undercover as a file clerk in the office of Cypher Headquarters (filmed at the Brookmans Park Transmitting Station, located north of London), owing to M12's operatives having fatally failed, the Forces of Evil plainly being a specially tough foe here, possibly masquerading as a glass cleaning enterprise. "Mother" (Patrick Newell), a seventh season addition to the series as wheelchair bound supervisor of the dauntless agent pair, determines their assignment here and interestingly rails in opposition to agents who are dependent upon "gadgets", a gibe at the contemporaneous James Bond films. He need not concern himself, however, with the workaday methods of Steed and Tara that are comprised of cunning rather than gimmickry. Steed and his beautiful workmate change apparel frequently throughout the piece, adding interest for costume conscious devotees of the programme. Additionally, there are some ingenious and well-designed sets, although over half of the scenes are filmed on location, rather than within a studio. Director Hough ably takes advantage of all of this to effectively deploy his camera. There is a goodly number of interesting players on board, with acting laurels being shared by ever engaging Ivor Dean, as an agent working with Steed and Tara, and Nicholas Smith, the episode's chief evildoer.