Kindly old doctor "Prof. Kristen" (Ralph Morgan) finds himself amidst a spate of brutal murders - but it's only when he is told that his pregnant mother was bitten by a bat before he was born, that he considers that he might be the man responsible - especially as he has become prone to blackouts when it gets truly dark. It's a wee bit predictable, but there is enough to keep it interesting with a ver mais...