At Maplewood Elementary, nothing exciting ever happens-until Principal Barker goes missing in the middle of school picture day. His half-eaten sandwich is found on his desk, his office chair still spinning, and the only clue left behind is... a suspiciously large shoeprint in the custodian's mop bucket.

While the adults call the police, three unlikely detectives-Omar (the brainy rule-follower), Lila (a chaos-loving prankster), and Benji (who's just here for the snacks)-decide to investigate on their own. After all, no one knows the school's secret passageways, janitor closets, or vending machine quirks better than the kids who live through them every day.