The Spy in Black is a praiseworthy film on international espionage during World War I.
The plot [adapted by Roland Pertwee from a novel by J. Storer Clouston], while necessarily melodramatic, is always within the range of possibility. Conrad Veidt, as captain of a German submarine, receives instructions to proceed to the Orkney Islands, where he’s to meet a woman spy, from whom he’s to take orders. She instructs him to sink 15 British ships cruising off the coast of Scotland, and contacts him with a discharged traitorous lieutenant of the British Navy.
Veidt has a strong role for which he’s admirably suited. Sebastian Shaw is excellent as the English naval officer. Valerie Hobson, as the other spy, is creditable.