Old School (en Inglés) - Gordon Korman

For all of Kat's life, it's just been her and her mother, Jamie--except for the forty-eight hours when Jamie was married and Kat had a stepbrother, Liam. That all ended in an epic divorce, and Kat and Liam haven't spoken since.

Now Jamie is a jewel thief trying to go straight, but she has one last job--at billionaire Ross Sutherland's birthday party. And Kat has figured out a way to tag along. What Kat doesn't know, though, is that there are two surprise guests at the dazzling Sutherland compound that weekend. The last two people she wants to run into. Liam and his father--a serial scammer who has his sights set on Ross Sutherland's youngest daughter.

Kat and Liam are on a collision course to disaster, and when a Sutherland dies, they realize they might actually be in the killer's crosshairs themselves. Somehow Kat and Liam are the new targets, and they can't trust anyone--except each other.

Or can they? Because if there's one thing both Kat and Liam know, it's how to lie. They learned from the best.