Nancy and Ned are off to Southern California to visit Josh Kline and his younger sister, Rachel. But when Rachel disappears from her high school commencement, Nancy learns that the girl has graduated into a world of trouble. She's fallen into an ultra-rich, ultra-chic, ultra-dangerous LA scene.

One of the guys Rachel's been hanging out with has a taste for hot cars and a distaste for all the rules. He's a prime suspect in a wave of burglaries in the Hollywood hills, but a secret society calling itself the Kats warns Nancy off the case. Rachel's playing with fire, and Nancy knows she has to find out what makes the Kat clique tick before Josh's little sister gets burned.