British Captain Terence Stevenson (Robert Donat), skilled in Romanian, German, and chemical engineering, embarks on a perilous undercover mission during World War II. Parachuted into Romania, he assumes the identity of Captain Jan Tartu, a fascist Iron Guard member, with orders to infiltrate a Nazi poison gas factory in Czechoslovakia and sabotage its operations. After his intended contact is arrested, Tartu secures a foreman position at a munitions plant. He lodges with landlady Anna Palacek (Phyllis Morris) and her daughter Paula (Glynis Johns), and encounters the likes of German Inspector Otto Vogel (Walter Rilla) and the enigmatic Maruschka Lanova (Valerie Hobson), who mingles favorably with the German occupiers but is revealed as a Czech resistance member. Gaining Paula's confidence by protecting her after she shoots a German officer, Tartu seeks help from the resistance, led by Dr. Novotny (Martin Miller). When Paula is caught trying to sabotage the factory, she urges Tartu to denounce her to protect his cover—she is executed, leaving the resistance suspicious of Tartu's loyalty. Maruschka plots to have Tartu eliminated, but an assignment to the gas plant gives him a final chance to complete his mission. Working under Dr. Willendorf (Percy Walsh), Tartu learns the gas's first shipment is imminent. In a desperate move, he pretends to betray resistance members in a bar, ensuring the underground abducts him. He ultimately convinces them he is an ally and devises a plan to destroy the plant. Despite his cover being blown, Tartu successfully rigs the plant with bombs and escapes with Maruschka and a pilot, flying off in a stolen German bomber as the plant explodes. Cast: - Robert Donat as Captain Terence Stevenson - Valerie Hobson as Maruschka Lanova - Walter Rilla as Inspector Otto Vogel - Glynis Johns as Paula Palacek - Phyllis Morris as Anna Palacek - Martin Miller as Dr. Novotny - Anthony Eustrel as German Officer - Percy Walsh as Dr. Willendorf - David Ward as Bronte - Mabel Terry-Lewis as Mrs. Stevenson - Frederic Richter as General Weymouth - John Penrose as Lieutenant in gas factory - Hubert Leslie as Peter Valek - Miki Iveria as Female worker at Skoda - Lawrence O'Madden as Col. Perry - Josephine Wilson as Nurse - Maurice Rhodes as Boy patient Runtime: 90 minutes.