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On a rainy evening in the Neustadt prison, Daniel, a hunchback, promises his cellmate, mad scientist Dr. Niemann, that when they are released, he will work for him for free if Niemann transfers his brain into a healthy body.  Soon after, a lightning storm destroys the prison, allowing Niemann and Daniel to escape and slip into the wagon of Professor Lampini's Chamber of Horrors, which carries the skeleton of Dracula.  Daniel kills Lampini, after which Niemann assumes the victim's identity and outlines his plans to find Dr. Frankenstein's records and continue his experiments, while wreaking his revenge on Ullman, Strauss and Hussman, the men who jailed him.

They travel to Reigelberg, where Hussman is the burgomaster, and set up Lampini's horror show.  The night Niemann arrives, Hussman's granddaughter-in-law Rita convinces Hussman, her husband Carl and police inspector Arnz to accompany her to the show.  There, Hussman scorns the Dracula exhibit, and after the curtain falls, Niemann restores Dracula to life by removing the stake from his heart, and sends him after Hussman.

Soon after, Dracula, calling himself Baron Latos, offers Rita, Carl and Hussman a ride home.  At their house, he kills Hussman, hypnotizes Rita with his ring and abducts her in his wagon, which is attached to Niemann's wagon.  When Carl calls the inspector and then chases after them, Niemann unhooks Dracula's wagon, stranding the vampire just as the sun rises and dooming him to return to his skeletal form.

Days later, as Niemann and Daniel enter the town of Frankenstein, Daniel falls in love with a gypsy dancer, Ilonka, and rescues her from her brutal boss.  Niemann allows her to accompany them, and although Ilonka turns away from the sight of Daniel's hump, she promises to be his friend.

That night, as Niemann and Daniel search the ruins of Frankenstein's castle for his records, they find the Wolf Man and the Monster encased in ice in a frozen cave beneath the earth.  After being thawed, the Wolf Man returns to his human form as Larry Talbot, and helps Niemann find the records, in return for which the scientist promises to find a new body for his brain.  They all travel to Niemann's laboratory in Visaria, and along the way, Daniel jealously watches Ilonka falling in love with Larry.

After a few days at the laboratory, Daniel and Larry grow impatient for Niemann, who is obsessed with regenerating the Monster, to help them.  Niemann then captures and kills Ullman and Strauss, at the same time that Daniel spitefully informs Ilonka that Larry is a werewolf.  She runs to Larry, and after he tells her that only a silver bullet shot by someone who loves him can end his misery, she fashions a bullet out of her silver bracelets just as the moon rises.

That night, the Wolf Man kills, and when the townspeople find the remains of his victims, they form a mob and descend on the castle, where Niemann is working on the Monster.  Meanwhile, Ilonka shoots the Wolf Man, but not until he fatally wounds her.  When Daniel finds them both dead, he blames Niemann and strangles him, waking the Monster, who kills Daniel to protect his master.  The mob enters the castle and pushes Niemann and his monster into the bog, where they quickly drown in the quicksand.