The Tiara on the Terrace by Kristen Kittscher

In this funny, clever novel, perfect for fans of Pseudonymous Bosch and Gordon Korman and a companion to The Wig in the Window, tween sleuths Sophie Young and Grace Yang go undercover at Luna Vista's Winter Sun Festival to catch a murderer before he—or she—strikes again.

Sophie Young and Grace Yang have been taking it easy ever since they solved the biggest crime Luna Vista had ever seen. But things might get interesting again now that everyone is gearing up for the 125th annual Winter Sun Festival—a town tradition that involves floats, a parade, and a Royal Court made up of local high school girls.

When Festival president Jim Steptoe turns up dead on the first day of parade preparations, the police blame a malfunctioning giant s'more feature on the campfire-themed float. But the two sleuths are convinced the mysterious death wasn't an accident.

Young and Yang must trade their high tops for high heels and infiltrate the Royal Court to solve the case. But if they fail, they might just be the next victims.