Three 12-year-old kids discover a Mummy (undead) in the basement of a "dead" man's house. It comes alive due to the conjunction of the moonlight during that time of the month. They are scared of him at first, but with time discover he is friendly, if clumsy and confused. The kids name the mummy Harold, and decide he will temporarily take up residence in one kid's bedroom. After paying a visit to their Halloween-obsessed friend, Bruce, they discover that if the mummy is not put back in his coffin before midnight on Halloween, the mummy will cease to exist.