In 1999, Petey Shelburn attempts to destroy a cursed drum-playing monkey at an antiques shop, but the monkey's drumming triggers a series of deaths, including the shop owner’s disembowelment. Petey disappears, leaving his wife Lois to raise twin sons, Hal and Bill. The boys discover the monkey and wind its key, causing a babysitter's accidental death. Bill's bullying of Hal leads to Lois’ aneurysm and death, and Hal disposes of the monkey. The twins move to Maine, but the monkey reappears, causing more deaths, including their uncle Chip’s. The twins throw the monkey down a well, hoping it’s gone for good.

Twenty-five years later, Hal is estranged from Bill and his son Petey, fearing the monkey’s return. After a series of fatal accidents in town, Bill reveals he has the monkey and plans to use it for revenge, believing Hal caused Lois' death. Bill insists Petey wind the monkey's key to save Hal. A local named Ricky forces Petey to retrieve the monkey, but when Bill tries to use it on Hal, the monkey triggers chaos, killing random people instead. Hal and Bill reconcile, but the monkey kills Bill by decapitation.

Hal and Petey, now determined to prevent further destruction, become the monkey's new owners. As they leave the ruined town, a mysterious figure representing the Pale Horseman acknowledges them. Hal suggests they honor Lois by dancing, and Petey agrees, signaling a tentative step toward healing.