Bloodsucking winged creatures who may take human shape appear to have returned after centuries of dormancy to the middle-European municipality of Kleinschloss in this atmospheric, low-budget thriller from small-scale Majestic Pictures, and the burgomaster (Lionel Belmore) demands answers. With victims scattered everywhere, all bearing the distinctive puncture marks, police detective Karl Brettschneider (Melvyn Douglas) finds himself completely stymied. Brettschneider, who refuses to accept what he considers mere superstition, is not pleased when that eminent physician Dr. Otto Von Niemann (Lionel Atwill) hints that there may indeed be such things as murderous human bats. Herman Gleib (Dwight Frye), the village idiot, meanwhile, just happens to have a fondness for the nocturnal creatures -- "They're so soft!" -- and the villagers, as they are wont to do, grab their torches and commence a manhunt. Poor Herman is destroyed, but there is another killing. And this time the victim is Georgiana (Stella Adams), Dr. Von Niemann's housekeeper, who failed to serve the physician his late-night coffee.