In the underground Facility, senior technicians Gary Sitterson and Steve Hadley discuss plans for a mysterious ritual. A similar operation undertaken by their counterparts in Stockholm has just ended in failure.
Five Michigan State University students, Ash Williams (Bruce Campbell) and his girlfriend Linda (Betsy Baker), accompanied by Ash's sister Cheryl (Ellen Sandweiss), their friend Scotty, and his girlfriend Shelly , venture into the Tennessee hills to vacation in an isolated cabin for their spring break. They soon run into trouble, first narrowly avoiding another motorist, then having a sudden scare as the bridge near the cabin begins to collapse as they cross. That night, while Cheryl is making a drawing of a clock, her hand becomes violently possessed by a mysterious entity, causing her to draw a picture that looks like a deformed, evil face. She fails to mention the incident to the others, dismissing it as her imagination.
The film begins with a new beginning similar to the first film. Ash Williams and his girlfriend, Linda, take a romantic vacation to a seemingly abandoned cabin in the woods. While there, Ash plays a tape recorder from the cabin's previous inhabitant Professor Knowby. The tape features Knowby reciting passages from the Necronomicon Ex-Mortis (or Book of the Dead), which he has discovered during an archaeological dig. However, the recorded incantation unleashes an evil force which kills and later possesses Linda, forcing Ash to decapitate his girlfriend with a shovel when she attacks him, he then buries her.
At University of Zurich Institute of Medicine in Switzerland, Herbert West brings his dead professor, Dr. Hans Gruber, back to life. There are horrific side-effects, however; as West explains, the dosage was too large. When accused of killing Gruber, West counters: "I gave him life!"
A meteorite lands on the farmland property of Nathan Crane (Claude Akins) in Tellico Plains, Tennessee. Local physician Alan Forbes (Cooper Huckabee) is unable to explain why the rock keeps shrinking. He is dissuaded from contacting the authorities by Charlie Davidson (Steve Carlisle), a realtor who does not want the new arrival to discourage the Tennessee Valley Authority (TVA) from establishing a new reservoir in the area. As the rock shrinks away to nothing, a glowing color seeps out and into the ground. Within a few weeks, the farm's crops bloom but are soon discovered to be inedible.
Dr. Edward Pretorius (Ted Sorel) is a scientist who has developed the Resonator, a machine which allows whoever is within range to see beyond normal perceptible reality. His assistant, Dr. Crawford Tillinghast (Jeffrey Combs), activates the machine and soon sees strange creatures in the air. When he is bitten by one of them, he urges Pretorius to turn the machine off. However, the crazed Pretorius refuses. Events transpire to the point where Crawford panics, fleeing outside. When the police arrive, they find Pretorius decapitated. Crawford is subsequently arrested and accused of murder.
In 1765, the inhabitants of the town of Arkham are suspicious of the strange phenomena surrounding the grand "palace" that overlooks the town. They suspect its inhabitant, Joseph Curwen, of being a warlock.
The film begins with the groaning of a woman. The camera slowly pans to show two elderly women (who look like twins) and an elderly man who are watching a woman writhe and moan with the pain of childbirth on a bed in an old-fashioned looking bedroom. She is then led out of the room by the elderly man, who is later revealed as the elder Whateley.
Stephen Reinhart, an American scientist (Nick Adams), pays a visit to the estate of his British fiancée's family. He finds a scorched area of countryside near an enormous crater. Local townspeople are hostile toward him and refuse to either drive him to his destination or talk about the family that lives there. The source of all these problems is later revealed to be a radioactive meteorite kept hidden in the basement by his girlfriend's father, Nahum Witley (Boris Karloff), who has been using the radiation to mutate plant and animal life, with horrific consequences to his subjects and to members of his family.
Claire Ward (Sibbett) hires private investigator John March (Terry) to look into the increasingly bizarre activities of her husband Charles Dexter Ward (Sarandon). Ward has become obsessed with the occult practices of raising the dead once practiced by his ancestor Joseph Curwen (Sarandon in a dual role). As the investigators dig deeper, they discover that Ward is performing a series of grisly experiments in an effort to actually resurrect his long-dead relative Curwen.
In the late 18th century, in the Winthrop house, something within it is screaming and banging at the walls of its confines. Joshua Winthrop, the owner of the house, rushes through the poorly lit corridors of the house before unlocking a heavily locked door. He begins talking to the creature inside to calm her down but she then kills him.
Susannah Kelton, a newly married twentysomething who was raised in foster care in the big city, learns that her real parents have only recently died and left all of their property to her. She and her husband, Mike, travel to the island of Dunwich off the coast of Massachusetts to inspect the property. They find a local culture that is clannish, backward and ignorant. The few friends they make amongst the locals, including Susannah's Aunt Agatha, warn them that the family mill is cursed and urge the Keltons to leave immediately and never look back. Refusing to bow to superstition, the Keltons consider rehabilitating the abandoned mill. They become the target of a gang of local thugs led by Susannah's lecherous cousin, Ethan. Their reign of terror is ended by something still living in the shuttered attic room of the mill, something that caused Susannah nightmares as a child.