Lady entomologist Lockwood is sent on a mission behind the Iron Curtain to gather information on possible biological warfare tests being conducted by the Enemy.

Well-done early Cold War thriller, partly comic, partly harrowing, helped by an excellent cast. Lockwood and Clark make a fun pairing, and Goring is excellent as a toad-like apparatchik. The comic ending isn’t as perfect an ending as it could be, but in the context of the period, the rationing jokes work well. Overall an excellent film, and makes an interesting triptych with Lockwood's other, better known, spying adventures, The Lady Vanishes and Night Train to Munich. Indeed, there is a sublime moment in this film, when Lockwood arrives in Zovgorod. She sees an old lady patiently waiting, and thinks it is her contact before realizing it isn't. Lockwood gives a wistful little smile, as if remembering a certain Miss Froy. A charming and subtle little in-joke, in a film that has many such nods.