A conniving trapeze artist named Cleopatra seduces a carnival sideshow dwarf named Hans after learning of his large inheritance, much to the chagrin of Frieda, his dwarf girlfriend. Cleopatra conspires with circus strongman Hercules to kill Hans and inherit his wealth. Meanwhile, other romances flourish among the sideshow performers: the Bearded Lady, who is in love with the Human Skeleton, gives birth to their daughter. The news is spread among the friends by the Stork Woman. Additionally, Violet, a conjoined twin whose sister Daisy is married to Roscoe, the stuttering circus clown, becomes engaged to the circus’s owner.
Hans, enamored of Cleopatra, ultimately marries her. At their wedding, Cleopatra begins poisoning Hans’ wine but drunkenly kisses Hercules in front of Hans, revealing her affair. Oblivious, the other “freaks” announce that they accept Cleopatra in spite of her being a “normal” outsider: they hold an initiation ceremony in which they pass a loving cup around the table while chanting, “We accept her, we accept her. One of us, one of us. Gooble-gobble, gooble-gobble.” Cleopatra’s mean-spirited amusement at this ceremony turns to fear and anger after Hercules jokes that the rest of the entertainers plan to turn her into one of them. She mocks them, tosses the wine in their faces and drives them away before berating Hans and drunkenly parading him around on her shoulders like a child. The humiliated Hans realizes that he has been played for a fool and rejects Cleopatra’s attempts to apologize, but then he falls ill from the poison.
While bedridden, Hans pretends to apologize to Cleopatra and also pretends to take the poisoned medicine that she is giving him, but he secretly plots with the other entertainers to strike back at Cleopatra and Hercules. In the film’s climax, Hans confronts Cleopatra with three of the entertainers as backup thugs. However, Hans’ circus wagon is overturned in a storm, giving Cleopatra the chance to escape into the forest, closely pursued by them. At the same time Hercules goes to kill seal trainer Venus for knowing about the plot. Venus’s boyfriend, Phroso, attempts to stop Hercules but is nearly killed before the rest of them intervene and injure Hercules, saving Phroso. They all pursue an injured Hercules.
Some time later, Cleopatra has been made into a grotesque, squawking “human duck” on display for carnival patrons; her tongue has been removed, one eye has been gouged out, the flesh of her hands has been melted and deformed to look like duck feet, her legs have been cut off, and what is left of her torso has been permanently tarred and feathered. In the original version of the film, it is revealed that after the freaks caught Hercules, they turn him into a castrato. Meanwhile, Hans, now living in a mansion off his inheritance, is visited by several of his sideshow peers, and reunited with Frieda.