A dream vacation on a luxurious yacht turns deadly in this pulse-pounding beach read, perfect for fans of Lauren Weisberger and Ruth Ware.    Belle likes to think herself immune to the dizzying effects of wealth. But when her best friend, Summer, invites her on a glamorous getaway to the Mediterranean aboard her billionaire boyfriend's yacht, the only sensible answer is yes. Once she's aboard the luxurious Lion's Den, it soon becomes clear that this jet-setting holiday is not as advertised. Belle's dream vacation quickly devolves into a nightmare as she and the other girls Summer invited are treated more like prisoners than guests by their vicious host. Belle is going to have to keep her wits about her-and her own big secret closely hidden-if she wants to make it off this yacht alive.   Includes a Reading Group Guide, exclusive epilogue, and sneak peak of Katherine St. John's next book, The Siren.