Louis Creed, his wife Rachel and their young children Ellie and Gage move to a remote woodland house on the outskirts of Ludlow, Maine. Ellie stumbles across a Pet Cemetery (misspelled "Sematary") in the woods after following a procession of children and encounters her neighbor Jud Randall who quickly strikes up a friendship with the family.
Louis who works at a university hospital is unable to save the life of a student called Victor Pascow who is hit by a car. Louis is plagued by nightmares of Victor warning him to stay away from the woods and claiming, "the barrier must not be broken". Meanwhile Rachel suffers from her own trauma regarding her sister Zelda who died as a teenager from spinal meningitis and whose illness traumatized a young Rachel.
Ellie's beloved pet cat Church is hit by a truck and is found by Louis and Jud. Aware of how devastated Ellie will be, Jud convinces Louis to bury Church deep in the Pet Sematary. The next day, Louis is stunned to discover Church is alive although he is notably more aggressive and dirtier, scratching Ellie and bringing a dead bird into the house. Louis confronts Jud who tells him that the Pet Sematary is able to bring things back from the dead and is inhabited by a Wendigo that the natives in the woods feared before fleeing. After finding Church sitting on Gage in his crib, Louis leaves Church on the side of the road and tells Ellie he ran away. Meanwhile Louis and Rachel's nightmares about Pascow and Zelda intensify.
The family throw a birthday party for Ellie. While playing hide and seek with her friends, Ellie spots Church in the road and rushes to him. Gage follows and is almost hit by a truck but is saved by Louis. The driver swerves to avoid Gage, causing a large tank to break loose which ends up hitting and killing Ellie who was still on the road. The family are devastated, and Rachel and Gage leave to spend a few days with Rachel's parents. Louis visits Jud who tells Louis that he knows that he's thinking of burying Ellie in the Pet Sematary and warns against it. Jud passes out from drinking and Louis takes the opportunity to dig up Ellie's body and bury it in the Pet Sematary. Ellie returns later that night, looking pale and with a notably meaner and colder attitude.
Meanwhile Rachel is spooked when Gage starts having nightmares and references Pascow by name. Rachel heads home, unable to contact Louis and calls Jud to check on him while she's stuck in traffic. Jud visits and is turned away by Louis. However, Jud spots Ellie watching him from her bedroom window, and he flees to his own house. As he gets his pistol to kill Ellie, Jud is surprised by Church and in the distraction, Ellie slices his ankle with a scalpel she stole from Louis. Ellie mocks Jud by taking the form of his dead wife Norma before stabbing Jud to death.
Rachel and Gage arrive at the house much to Louis's surprise. Ellie introduces herself to Rachel who is horrified and flees upstairs with Gage. As Louis tries to convince Rachel that Ellie is still their daughter, he notices that Ellie is missing and heads to Jud's house to find her.
Meanwhile Rachel is attacked by a knife wielding Ellie and is stabbed but manages to escape to the bathroom with Gage, barricading herself in. Louis finds Jud's body and returns to the house to see Rachel trying to lower Gage out the bathroom window. Louis catches Gage and Rachel is stabbed to death by Ellie. Louis locks Gage in the car and returns upstairs to find a dying Rachel who begs not to be buried in the Pet Sematary.
Ellie knocks Louis unconscious and drags Rachel's body into the woods where she buries her in the Pet Sematary. Louis awakens and finds Ellie in the woods where the pair fight. As Louis prepares to kill Ellie, he is stabbed by a resurrected Rachel and he too is buried. The trio burn Jud's house to the ground before approaching the car where Gage still sits inside. A resurrected Louis gestures to Gage who unlocks the car door before the film cuts to black.