In the film's prologue, Anna Müller takes a little girl in her care into woods to a castle, leaving behind her husband, the schoolmaster. At the castle, Count Mitterhaus, who is a vampire, feeds upon the child while Anna watches. She is aroused by that sight and afterwards the count makes love to her.
The villagers, led by Müller and the mayor, attack the castle and break in. Müller drives a stake through the Count's heart, who with his dying breath curses the villagers, vowing that their children will die to give him back his life. The villagers punish Anna by having her run the gauntlet until Müller stops it. Anna runs back to the castle and drags the Count's staked body to a crypt. Blood dropping from her wounds revive the Count for a short while and he tells her to find his cousin Emil. Meanwhile the villagers set the castle on fire.
Fifteen years Later, the village is ravaged by the plague and the leading citizens are debating whether this is merely a disease, as Dr. Kersch and Prof. Müller suggest, or due to the Count's curse, as Schilt and Hauser believe. Dr. Kersch suggests breaking through the quarantine blockade to get help and medical supplies and with the help of his young son Anton, he succeeds. Just before he leaves, a travelling circus, led by a dwarf and a gypsy woman, arrives in the village and the villagers appreciate the distraction from their troubles.
After the show, one of the artists, Emil, seduces the mayor's daughter Rosa and, revealing himself a vampire, barely restrains himself from biting her. Emil and the gypsy woman go to the castle, where they find the Count's staked body still lying in the crypt. The gypsy asks whether all must die, and Emil replies that all who led the attack on his cousin and all their children must die.
During the next performance, the circus features a Hall of Mirrors. During his visit, the mayor has a vision of a revived Count Mitterhaus and collapses. Frightened by this event, Schilt and his family try to flee the blocked town but the dwarf, who promised to help them, leaves them in the woods to be devoured by the circus panther to deter others from leaving.
Later that day, Müller's daughter Dora, who had been safely out of town, races through the woods and breaks the blockade to be with her father and her sweetheart Anton. In the woods, she comes across the dismembered bodies of the Schilt family. As she arrives at the village, her father, already suspicious of the circus, considers the circus animals the culprits, while Anton defends the circus, as he thinks it the only distraction from the plague, and takes Dora to the circus to show her that the circus animals are safe.
The same night, the twin acrobats lure Hauser's two boys into the Hall of Mirrors, where they bite them. After the boys' dead bodies are found, Hauser and the mayor begin to shoot the circus animals. The mayor also shoots at Emil, who however remains unharmed. The mayor collapses, dead by heart failure, while his daughter runs off with Emil. At the Count's tomb he bites and kills her.
Dora and Anton also visit the Hall of Mirrors. The twin acrobats try to bite Dora as well, but the cross she is wearing saves her. Later, the vampires enter the school house; Emil kills the students, while the gypsy (now revealed as Anna, the twins' mother) tears off the cross from Dora's neck, enabling the twins to attack her. Dora, however, escapes into the school chapel. She tosses a wooden cross unto the female twin, piercing her heart. This kills both twins simultaneously through their sibling's link, while the gypsy and Emil flee.
Meanwhile, Dr. Kersch has returned from the capital with an imperial escort and medicines for the plague. He also brings news of vampire killings in various other villages, all of them toured by the Circus of Night, and that Emil is Mitterhaus's kinsman. The men attack the circus, and Hauser sets fire to the Hall of Mirrors but is himself caught between a vision and the fire, burning along with the tent.
Dora is kidnapped and taken to the crypt, where Emil wants to resurrect the Count. Emil approaches Dora to drain her, but then the gypsy pushes her away to save her and he ends up biting the gypsy and kills her. As she falls down dead, her face is rejuvenated, revealing her to be Anna Müller. Anton, Müller and the soldiers enter the crypt, and Müller pierces Emil with the stake taken from the Count's chest before he himself dies. But then the Count, freed from the stake and fed on enough blood, rises from the sarcophagus. Anton fends him off, with his crossbow serving as a provisory cross, and decapitates the vampire with the drawstring. As Anton and Dora exit the tomb, the villagers set the ruins alight with torches.