Pet Sematary is the story of Louis and Rachel Creed, who move to a small town in Maine with their children Gage and Ellie. After their cat is hit by a truck, the Creeds' neighbor Jud tells Louis that if he buries it behind the local pet cemetery, it will come back to life. When tragedy strikes the Creed family, Louis is tempted to use the cemetery again, but this time, the stakes are higher. This horror novel examines themes of death and wish fulfillment.
Louis Creed, a doctor from Chicago, is appointed director of the University of Maine's campus health service. He moves to a large house near the small town of Ludlow with his wife Rachel, their two young children, Ellie and Gage, and Ellie's cat, Church. From the moment they arrive, the family runs into trouble: Ellie hurts her knee after falling off a swing, and Gage is stung by a bee. Their new neighbor, an elderly man named Jud Crandall, comes to help. He warns Louis and Rachel about the highway that runs past their house; it is constantly used by speeding trucks.
Jud and Louis quickly become close friends. Since Louis' father died when he was three, he sees Jud as a surrogate father. A few weeks after the Creeds move in, Jud puts the friendship on the line when he takes the family on a walk in the woods behind their home. A well-tended path leads to a pet cemetery (misspelled "sematary") where the children of the town bury their deceased animals. This provokes a heated argument between Louis and Rachel the next day. Rachel disapproves of discussing death, and she worries about how Ellie may be affected by what she saw at the "sematary". (It is explained later that Rachel was traumatized by the early death of her sister, Zelda, from spinal meningitis—an issue that is brought up several times in flashbacks.)
Louis himself has a traumatic experience during the first week of classes. Victor Pascow, a student who has been fatally injured in an automobile accident, addresses his dying words to Louis personally, even though the two men are strangers. On the night following Pascow's death, Louis experiences what he believes is a very vivid dream in which he meets Pascow, who leads him to the "sematary" and warns Louis to not "go beyond, no matter how much you feel you need to." Louis wakes up in bed the next morning convinced it was, in fact, a dream—until he finds his feet and the bedsheets covered with dirt and pine needles. Nevertheless, Louis dismisses the dream as the product of the stress he experienced during Pascow's death, coupled with his wife's lingering anxieties about the subject of death.
Louis is forced to confront the subject of death at Halloween, when Jud's wife, Norma, suffers a near-fatal heart attack. Thanks to Louis's prompt attention, Norma makes a quick recovery. Jud is grateful for Louis's help and decides to repay him after Church is run over outside his home at Thanksgiving. Rachel and the kids are visiting Rachel's parents in Chicago, but Louis frets over breaking the bad news to Ellie. Sympathizing with Louis, Jud takes him to the pet sematary, supposedly to bury Church. But instead of stopping there, Jud leads Louis farther on a frightening journey to "the real cemetery": an ancient burial ground that was once used by the Micmac Indians. There Louis buries the cat on Jud's instruction, with Jud saying that animals buried there have come back to life.
Not really believing, Louis thinks that the subject is finished– until the next afternoon when the cat returns home. But it is obvious that Church is not the same as before. While he used to be vibrant and lively, he now acts ornery and "a little dead", in Louis's words. Church hunts for mice and birds much more often, but he rips them apart without eating them. The cat also smells so bad that Ellie no longer wants him in her room at night. Jud confirms that this condition is the rule, rather than the exception, for animals who have been resurrected in this fashion. Louis is deeply disturbed by Church's resurrection and begins to wish that he had neverdone it.
Two-year-old Gage is run over by a speeding truck several months later, and Louis very nearly manages to prevent the accident. Overcome with despair, Louis considers bringing his son back to life with the help of the burial ground. Jud, guessing what Louis is planning, attempts to dissuade him by telling him the gruesome story of the last person who was resurrected by the burial ground. Jud concludes that "the place has a power... its own evil purpose," and may have caused Gage's death because Jud introduced Louis to it.
Despite this, and his own reservations about the idea, Louis's grief and guilt spur him to carry out his plan. Gage returns from the dead as a monstrous, demonic shadow of his former self and kills both Jud and Rachel. Louis confronts his son and sends him back to the grave with a lethal injection of chemicals from his medical supply stock. After burning the Crandall house down, he returns to the burial ground with his wife's corpse, thinking that if he buries the body faster than he did Gage's there will be a different result. The book ends with Louis sitting with his back to the door playing solitaire listening to Rachel's reanimated corpse walk up behind him to drop a cold hand on his shoulder while her voice rasps, "Darling."