When a neutral Danish merchant ship is forced to put into port after trying to evade British wartime contraband control, its captain becomes involved in a beautiful British Naval Intelligent agent's efforts to capture a group of German spies operating from a London cinema.
When Conrad Veidt's Danish freighter is routinely stopped by the Royal Navy in search of contraband; he is held over for 24 hours. He manages to get hold of two shore passes for himself and his first mate, but they are stolen and as he investigates, he encounters Valerie Hobson, the mysterious "Mrs. Sorensen" and soon is embroiled in a top secret Nazi espionage conspiracy. Just as with "the Spy in Black" (1939) the two stars gel well, Weidt has a sort of suave, debonair style about him that complements his stylish co-star well and the writing gives ample opportunity for some humour as the gently suspenseful, if maybe just a tad too contrived, mystery moves along. Set at the start of WWII, the storyline lacks some of the more sinister aspects of later British-made war films, and much of the style and pace of the story still depicts an optimism that the conflict would be short-lived.