Plot
Three couples meet for one last party before vacating a lakeside cabin. As the couple play cards, Holly goes to shower. A scream is heard and Holly is discovered in the shower dead, her entrails ripped open and her baby (she was pregnant) gone. Marc Denning becomes the sole survivor of a bloody massacre which claims the lives of his lover, his brother, and three friends. Another of the women is found hung upside down in the living room, her throat cut, while the last woman is dragged out the window by a tree branch, apparently to her death. Something with glowing red eyes attacks the men. After being assaulted by a zombie-like creature whose eye he rips out, Denning stumbles to the nearby highway where he is hit by a car.
He wakes up in the hospital with a broken leg and three broken ribs. The police begin to investigate the murders. Shortly after the murders, Denning also begins to look for answers that will explain the slaughter.
Meanwhile, a red-caped tarot reader named Brother Magnus reads the cards for an unidentified Southern-accented woman. He tells her she has to leave urgently. As she does so, she is attacked by something. Then a shadowy red-eyed cowled figure appears in the doorway of Magnus's house. He shoots at it, but the bullets bounce off. The cowled figure zaps Magnus with an energy ray.
Denning is investigating at the library when a woman, Reggie, a survivor of a previous massacre, introduces herself. These two then travel with the detective, Lieutenant Leo Ball, to the house of a psychic, Ben, who had assisted Leo previously. Ben is identical to Brother Magnus. He has left a box of old books for Leo to examine. These include The Necronomicon, a book called Lost Gods, one called The Gate and the Key by C. D. Ward and The Chronicles of Yog-Kothag. Denning becomes convinced that the murders are sacrifices rather than serial killings, especially when he reads a letter left by Ben that says "He's coming back." Denning takes "he" to refer to the old god, Yog-Kothag.
Reggie and Denning join forces over coffee at Denning's house, where a sinister dog who showed up before shows up again. Leo teaches Denning to use a gun, while Denning shows him a magazine article about quasars. He has a theory that the killings coincide with pulsings of certain quasars in certain years. Leo is skeptical.
Reggie and Denning go to a movie called The Jet Benny Show . Leo receives a document via mail which he opens and then remails to Denning. As goes to mail the envelope, Leo witnesses a boiling cloud and a ray that zaps a car. Shortly after, he is attacked by something and dies. Denning wakes from a dream, realizing Leo is in trouble and races to the scene. The police are taking Leo's body away.
Denning maintains contact with a professor via telephone regarding the pulsing of quasars. One is set to pulse on the coming Thursday. He also realizes, after his secretary, Lisa, plots the killings on a map, that the killings form a pentagram, which is the 'evil' symbol of Yog-Kothag as depicted in the Yog-Kothag book. At the center of the pentagram lies the Nash real estate agency. Denning explains that Yog-Kothag was an old god who was "so bad that the other gods ganged up on him and imprisoned him on a quasar."
The zombie reappears and attacks Denning and Reggie. They try to kill it multiple times, thrusting a firepoker through it, hitting it with their car and finally setting its body on fire, but it comes back to life each time. Finally, it tracks them and, after Reggie confesses she is in love with Denning, the zombie stabs Denning with a mystical dagger. Denning extracts the dagger and stabs the zombie with it.
Nash seems to witness the reappearance of Holly. She rips open her womb and takes out a baby, which falls to the ground. It appears demonic and has glowing red eyes. Slightly later Nash appears to be attacked by this baby, but then he awakes – it was only a dream.
Reggie goes to confront Nash, witnessing the sinister dog again and soon learns Nash has superhuman powers. He is resistant to bullets and is able to prevent a paperweight that she throws at his head from striking him. Nash shows Reggie the document which Leo mailed to Denning, but which never arrived. It is Nash's birth certificate, showing that he was born over a hundred years ago. The apparent mysterious and supernatural cult dedicated to bringing Yog-Kothag back to Earth is in fact just Nash, and his zombie. Together they committed a series of periodic ritual murders over the last decades. The zombie is now dead, but Nash reveals that Denning has been transformed into a new zombie. Yog-Kothag speaks through Denning with a warning. Denning then asserts himself and stabs Nash with the mystical dagger.
The film ends as Nash seems to be drawn screaming into the cosmic void. Yog-Kothag's voice is heard proclaiming "Worm! Thou hast failed me!" The ending text reads, "Somewhere, a man named Nash is screaming."
