12-year-old friends, Marshall, Gilbert and Amy accidentally revive a mummy they discover in a neighbor's basement. They affectionately name the mummy Harold, and must rush to return him to his resting place before midnight on Halloween.

Amy is preparing for her father’s Halloween-themed wedding to his fiancé Carl, when Amy, Gilbert and Marshall discover that their mummy friend Harold and his beloved Rose may be in danger. Stobek, an evil mummy with a thousand-year-old grudge against his best friend-turned bitter rival Harold, is unexpectedly awakened and out for revenge. With help from his hypnotized lacky Larry, Sobek kidnaps Rose, and Amy, Gilbert, Marshall, Buzzy, and Harold must use their skills once again to save her and get back in time to attend the wedding.