A young woman named Arletty (Marianna Hill) drives to the beach town of Point Dume, California, to visit her estranged father, an artist. She finds his beachfront house abandoned. He left a diary in which he addresses her specifically. In it he complains about darkness consuming the town, and horrible nightmares he is having, and implores Arletty to never, ever look for him. His letter tells her to talk to the owner of the art gallery, who sells his paintings. The gallery owner says he has none of her father's paintings, does not sell them, no one ever comes in looking to buy his works, and says he doesn't know where he went. He says Point Dume is "an artist colony" and he only vaguely remembers her father (his paintings are eerie pop art portraits of groups of people in black, white, and gray, standing; the men are always dressed in black suits, white shirts, and black ties, like dead men at a funeral). It is never clear if these are townspeople, or figures from his visions, or both.
Arletty meets a visiting Portuguese-American aristocrat Thom (Michael Greer) and his two extremely provocative, groupie-like female companions, Toni (Joy Bang) and Laura (Anitra Ford). Back at his motel, Thom interviews Charlie, (Elisha Cook, Jr.) the local town eccentric. Charlie speaks at length about "the blood moon" and "the dark stranger" and how he has lived through both. He says very soon it will be the 100 year anniversary of the first appearance of the "dark stranger." He will return, the moon will turn red, and the town will be overrun with evil. Charlie warns Arletty about her father, he says he is "one of them" now. Moments later he is murdered off screen.
Thom, Toni, and Laura are kicked out of their hotel after interviewing Charlie, and stay at Arletty's father's house. Arletty reads through her father's bizarre journal entries, in which he reveals his body temperature is 85 degrees, and he mentions fighting his "condition." Meanwhile, each night, creatures gather on the beach in front of bonfires, staring straight up at the moon. The locals call it "The Waiting."
Late one evening before making a trip to San Francisco, Laura goes into the local Ralphs supermarket, and is devoured by a hoard of vampires who are feasting on raw meat; the following day, Toni goes to see a movie, and is also eaten by the other theater patrons, who are the same creatures. That evening, the "blood moon" rises, and the town's residents turn into vampires, and the titular "Messiah of Evil" returns. Through voice-over of Charlie's taped interviews, we learn that this "Messiah" was a former minister and a Donner Party survivor from the late 19th century turned vampire/cannibal, who has come to spread his new "religion" and lead his people up the coast and inland. While Thom hides, two policemen in riot gear drive up and fire their guns into a swarm of vampires; however, one of the cops suddenly begins to bleed, causing his now-former partner to shoot him and flee. Undaunted, the undead cop shoots his former ally, and he and the other vampires go to feast on his flesh.
Thom returns to the house, where he finds Arletty half-crazed; she is cold, cannot feel pain, and thinks she may be dead or undead. She even finds a bug crawling around in her mouth and immediately vomits up various beetles, mealworms and an anole. While Thom was gone, Arletty was visited by her father, who had warned her not to follow him and begs her to leave to tell the world about Point Dume. He then attacks her, reluctantly giving in to his "vampire" urges, and after she stabs him with garden shears before burning him alive. Startled by Thom, she stabs him in the arm with the shears. The two of them flee to the beach, but the ersatz vampires follow them, even in broad daylight. They swim out to the breakers, but Thom drowns. Arletty survives and is captured by the townspeople. Instead of killing her, she is let free under the condition that she spread word of the religious movement throughout California and the world. This causes her to be locked up in an insane asylum. Each day, all day, she sits in the sun painting, dreading the day the Messiah and his followers come to take her away.
