Professor Paul Kristan [Ralph Morgan] doesn't know that his mother was bitten by a vampire bat just before he was born. The doctor who delivered the baby some 40 years ago in a bat-infested cave within earshot of angry native drums in the darkest reaches of Africa, handed the bundle of joy to his colleague, Doctor Anders Bizet [Pedro de Cordoba], who raised the boy as his own son. Paul is now a grown man, beloved by everyone in the village because of his "goodness", and engaged to be married to the flower of the village, the beautiful Marguerite Mane [Maxine Doyle].

Then the murders start. Three victims have been found lying in the caves, their throats torn open and the blood drained from their bodies. The cry goes up that this the work of a huge and loathsome vampire bat that kills during the dark of night and then carries the bodies into the caves. Only young David [Russell Gleason] cannot accept that there is a bat large enough to carry a human body. The good Professor isn't certain that it's a bat, but he is sure of one thing...the creature strikes only in the dark. Therefore, he suggests that everyone stay home after dusk and keep their lights burning.