Such Charming Liars by Karen McManus

The brand-new mystery thriller from the author of the One of Us Is Lying series, Karen M. McManus.
For all of Kat's life, it's been her and her mother, Jamie - except for 12 years ago, when Jamie was married for two days and Kat had a stepbrother, Liam. But all that ended in a swift divorce.

Now Jamie is a jewel thief trying to go straight, but she has one last job, at a billionaire's 80th birthday party. Neither Kat nor her mother know about two surprise guests: Liam and his father, a serial scammer with his own sights set on Ross Sutherland's family.

Kat and Liam are on a collision course to disaster, and when someone dies, the two teens realize they might be in the killer's crosshairs. They can't trust anyone except each other. Or can they? Because if there's one thing both of them know, it's how to lie...