Twin brothers Hal and Bill Shelbourne (both played by Christian Convery) have never had a good relationship due to Hal being timid and Bill being a bully. The two come into possession of a drum-playing toy monkey that belonged to their absent father. When the key on The Monkey’s back is turned, it plays a tune on the drum before someone nearby dies in a horrible accident. The boys’ babysitter, Annie (Danica Dreyer), is accidentally decapitated at a hibachi restaurant. Hal tries to use The Monkey on Bill after getting sick of his bullying, but this causes the death of their mother, Lois.

The boys seemingly get rid of The Monkey after their Uncle Chip is trampled by horses on a camping trip, but 25 years later, their Aunt Ida dies in a freak accident when The Monkey resurfaces. Hal (Now played by Theo James) is alone and only sees his son Petey (Colin O’Brien) once a year. He is contacted by Bill when The Monkey reappears, forcing Hal to go back to Ida’s house to settle her estate. He learns from the real estate agent (who gets blown to pieces thanks to The Monkey) that other people have suffered terrible accidents recently.

Bill was the one who was activating The Monkey to try and kill Hal since he knew Hal caused their mother’s death. Bill gets a local delinquent, Ricky, to abduct Hal and Petey so that Petey can turn The Monkey on and kill Hal. A swarm of wasps instead kills Ricky. Bill tries to force The Monkey to kill Hal, which ends up triggering a catastrophic incident that wipes out half the town. Hal and Bill eventually reconcile, but The Monkey triggers one of Bill’s booby traps, causing a bowling ball to crush his head.

Hal and Petey take The Monkey with them, and Hal resolves to spend more time with his son.