Locker 37 at Hopewell Elementary has been helping fourth graders solve their problems for as long as anyone can remember. So when Riley Zimmerman needs help pulling off the most ridiculous and wonderful prank the school has ever seen, the magical Locker 37 provides her with an equally ridiculous and wonderful rainbow hat that can clone anything that wears it. But will a group of clones, an untrustworthy bully, and 10,000 Ping-Pong balls be enough to help Riley pull off the most legendary prank in Hopewell's history?