In a mental institution, a patient named Arletty Lange remembers the following story: Upon receiving a letter from her artist father, Joseph Lang, who fears someone is coming after him, she drives through the night and stops at a gas station. A pickup truck, driven by a tall albino man, arrives and the station attendant notices three dead bodies under a blanket in the truck bed. After the attendant orders Arletty away from the station, the Albino also leaves, but as the attendant later works on a car, another man attacks and rips him apart with his bare hands. Meanwhile, Arletty finds her father’s beach house abandoned and discovers a diary that details his descent into madness. The next day, an art dealer informs Arletty that three strangers are looking for Joseph Lang, and reveals their hotel room number. There, Arletty finds a well-dressed couple, Thom and Laura, talking with a homeless man named Charlie, who explains that for over a hundred years, the townspeople descend into cannibalism when the moon turns red. When the third stranger, a young woman named Toni, enters, Charlie leaves in fear. Thom then tells Arletty that he wanted to interview her father, Joseph, but could not find him. As she leaves the hotel, Arletty is confronted by Charlie, who insists that she not bury Joseph, but burn him instead—insinuating that her father is dead. The next morning, Arletty is awakened by sounds coming from the bathroom and finds Thom, Laura, and Toni in various stages of undress. Thom explains they were evicted from their motel after Charlie’s body was found in an alley, apparently torn to pieces by dogs. Arletty agrees to let them stay and learns that Thom is gathering legends about the red moon. That night, Thom spots a group of people dressed in black standing around bonfires on the beach. He later flirts with Arletty, unaware that Laura is watching. Tired of sharing Thom with other women, Laura plans to leave. Hitchhiking, Laura is picked up by the Albino, who has four people, mesmerized by the full moon, sitting in the truck bed. Laura gets out of the truck when she sees the Albino eat a live rat. She walks to town and finds it deserted, except for a pale man she sees walk into a grocery store. She follows and sees the townspeople devouring raw meat in the butcher section. As Laura tries to flee, the townspeople eat her alive. The next day, Arletty is alerted by police that Joseph’s body was found on the beach, crushed under the large metal sculpture he was assembling. She goes to the beach, but only sees the hand of a corpse sticking out from under collapsed metal. Later, Arletty reads in Joseph’s diary that her father’s body temperature dropped to eighty-five degrees, and he feared he was possessed. She looks in the mirror and sees a trickle of blood coming from her ear. Just then, Thom walks in, and the startled Arletty burns her hand on the stove, but does not feel pain. As Thom washes the burn, he looks outside and sees a red moon. Arletty tells Thom that she did not recognize the dead man’s hand on the beach, and that the corpse is not her father. Meanwhile, Toni goes to see a Western movie, but after she enters the theater, the box-office closes. Engrossed in the film, she fails to realize that behind her the theater is filling up with the people from the grocery store. When the movie ends, Toni is devoured by the zombie-like audience. As Thom searches for Toni, a woman bites him, but he escapes, only to be followed by a crowd of townspeople. Two officers arrive in a police cruiser and start shooting at the crowd, but one cop notices his partner crying tears of blood and shoots him in the face. However, the gunshot has no effect, and the wounded cop rebounds to kill his partner. Forgetting Thom, the crowd devours the downed policeman. Meanwhile, Arletty looks in the mirror and sees a bloody tear on her cheek, then regurgitates lizards, cockroaches and maggots into the sink. When she regains consciousness, she sees Joseph in the shadows. He explains that one hundred years ago, a hunter met a member of the Donner party who claimed to have sold his soul to a “dark master” and become a cannibal, chosen to spread the dark master’s religion. Later, a search party discovered the dying hunter had been bitten by the cannibal. The hunter, in turn, bit one of his rescuers. The dark stranger watched from the shadows, then walked into the sea, announcing he would return in one hundred years. Joseph explains that Arletty must get the authorities to quarantine the town before the “black messiah” returns. Then, overcome with hunger, he steps from the shadows, revealing his half-eaten face, and attacks his daughter, who stabs him with scissors and sets him on fire. When Thom arrives, Arletty stabs him with a butcher knife, but she soon realizes that Thom is not a cannibal. As she binds his wound, the townspeople smash the windows. Thom kills one with a fireplace poker and escapes with Arletty while the crowd devours one of their own. On the beach, Thom and Arletty spot a small boat and try to swim out to it, but Thom drowns. The townsfolk capture Arletty, dress her in a robe, and place her on the beach as an offering to the “black messiah,” who emerges from the ocean and lets Arletty go, knowing no one will believe her story of cannibalism. When Arletty escapes, authorities think she has lost her mind and commit her to an insane asylum.