Ash Williams and his girlfriend, Linda, take a romantic vacation to a seemingly abandoned cabin in the woods. While in the cabin, Ash plays a tape of archaeologist Raymond Knowby, the cabin's previous inhabitant, reciting passages from the "Book of the Dead", Necronomicon Ex-Mortis, which he has discovered during an archaeological dig. The recorded incantation unleashes an evil force (also known as the Kandarian Demon) that kills and later possesses Linda, turning her into a "deadite". Ash is then forced to decapitate her with a shovel and bury her in a shallow grave near the cabin. At dawn, the evil force throws Ash through the woods. He briefly becomes possessed by the demon, but when day breaks, he is inexplicably returned to normal.
He attempts to flee the area but finds that the bridge to the cabin has been destroyed. The spirit chases him back to the cabin, where Linda's revived head attacks him and bites his hand. He runs to the shed, where her headless body attacks him with a chainsaw, but he overpowers and slashes the deadite Linda to death. His right hand becomes possessed and tries to kill him, and he severs it with the chainsaw before attempting to shoot it with a shotgun, but the hand mocks him and ultimately escapes. Meanwhile, Knowby's daughter Annie, and her research partner, Ed Getley, return from the dig with the missing pages of the Necronomicon, only to find the destroyed bridge. They enlist repairman Jake and his girlfriend Bobby Joe to show them another route to the cabin, where they find an embattled Ash covered in blood. Thinking that he murdered Annie's parents, Annie and the others lock him in the cellar.
The four new arrivals listen to the rest of Knowby's recording, detailing how his wife Henrietta was possessed by the Kandarian Demon, and that he killed her and buried her in the cellar. Henrietta, now a deadite, possesses Ed; Ash dismembers him with an axe. Bobby Joe tries to escape, but demonically possessed trees attack and drag her to her death. Annie translates two of the Necronomicon's pages before Jake turns on them and throws the pages into the cellar, forcing them at gunpoint to find Bobby Joe. Ash becomes possessed once again and attacks Jake. Annie retreats to the cabin and accidentally stabs Jake (mistaking him for the possessed Ash) before Henrietta kills him. Deadite Ash tries to kill Annie, but returns to his normal self upon seeing Linda's necklace.
With Annie's help, Ash modifies the chainsaw, attaches it to the stump of his right arm, and cuts the shotgun's barrel. After finding the missing pages of the Necronomicon in the cellar, Ash kills Henrietta. The trees outside begin to destroy the cabin. Annie reveals that she has only read the first half of the incantation and attempts to finish the second half. As she reads it, Ash's severed hand uses a Kandarian dagger to stab her in the back. She manages to complete the incantation before succumbing to her wound. The incantation opens up a whirling temporal vortex which not only draws in the demon, but also Ash and his Oldsmobile Delta 88.
Ash and his Oldsmobile land in the Middle Ages. A group of knights confront him and initially mistake him for a deadite, but are quickly distracted when a real harpy-like deadite appears. Ash blasts it with his shotgun and they hail him as a hero who has come to save them, causing him to break down and scream in anguish.
