In this eerie tale beginning deep within the African wilderness, a group of explorers seeks refuge in a secluded cave. Among them is a pregnant woman who, in a terrifying encounter, is bitten by a vampire bat. As the story leaps forward in time, it transports us to a quiet European village plagued by a string of unusual and sinister murders. The villagers, fearing the worst, band together in a mob with flaming torches, gathering at the house of Professor Ralph Morgan after each new killing. Their suspicion quickly points to a monstrous, giant bat as the culprit behind these deadly attacks.
Professor Kristan offers guidance, reassuring the villagers that a rational, scientific explanation for the murders exists, and urges them to stay calm and safe. Despite his calm demeanor, a dark secret lurks beneath his composed exterior. As the story unfolds, it becomes apparent that Kristan is not just an innocent scientist—he is the source of the terror. He begins to suffer from mysterious attacks, especially at night or in darkness, which induce a trance-like state. During these blackouts, Kristan becomes a remorseless killer, attacking and murdering villagers without any memory of his actions when he regains consciousness, believing himself to have simply fainted or passed out.
The only person aware of Kristan's condition is his loyal companion, Zan (played by Mischa Auer), a hunchback who closely follows his master's movements, ensuring that Kristan does not reveal his dark secret. Zan's unwavering loyalty is vital, as he witnesses Kristan succumb to the murderous trance time and again, but he keeps this knowledge hidden from the villagers to protect his friend.
Trouble heightens when Dr. Bizet (played by Pedro de Cordoba), a respected colleague and old friend of Kristan, arrives for a visit. During his stay, Dr. Bizet begins to suspect something is profoundly wrong with Kristan. He eventually reveals a shocking family history: Kristan's mother was bitten by a vampire bat, and due to Lamarckism—a theory suggesting that traits acquired during a lifetime can be inherited—these vampiric tendencies might have been passed down to him. This revelation clearly connects to the opening flashback, where the pregnant explorer (who was Kristan’s mother) was bitten and became a vessel for the dark curse.
The tension reaches its breaking point when Kristan’s betrothed, played by Maxine Doyle, is attacked while Kristan is entranced. The villagers, now fully convinced that something supernatural is at play, suspect Zan—the only one who seems to understand the true nature of Kristan—and chase him helplessly to the edge of a perilous cliff inside a dark cave.
In a moment of profound confession and despair, Kristan admits to the murders, desperately trying to clear Zan of suspicion. Despite Zan's protests, which are driven by his desire to save Kristan from himself, the villagers are convinced that Kristan is the villain. As the mob watch with bated breath, Kristan chooses to end the nightmare by throwing himself off the cliff, with Zan following in an act of loyalty and sorrow.
This haunting story weaves themes of inheritance, the supernatural, and tragic sacrifice, leaving viewers with a chilling reflection on the darkness that can reside within even the most seemingly benign minds.
