"Based on fact, this carefully reconstructed story of espionage in Belgium during World War One was one of the biggest British films of its year, and from the peak period of its director, Victor Saville. Though more concerned with characterization and suspense than with spectacular action, it holds interest throughout and is an unusually handsome production. Very rarely shown these days, this will be its first West Coast revival in many years. An unusually strong cast is headed by Madeleine Carroll, Conrad Veidt and Herbert Marshall" (William K. Everson). Madeleine Carroll portrays the Belgian nurse Marthe Cnockhaert, who spied for the Allies and attempted to blow up an arms dump to prevent a German gas attack.