On scholarship at a prestigious East Coast college, ordinary Mabel Dagmar is surprised to befriend her roommate, the beautiful, wild, blue-blooded Genevra Winslow. Ev invites Mabel to spend the summer at Bittersweet, her cottage on the Vermont estate where her family has been holding court for more than a century. Mabel falls in love with midnight skinny-dipping, the wet dog smell that lingers near the yachts, and the moneyed laughter that carries across the still lake while fireworks burst overhead. Before she knows it, she has everything she's ever wanted: friendship, a boyfriend, access to wealth, and, most of all, for the first time in her life, the sense that she belongs.

But as Mabel becomes an insider, a terrible discovery leads to shocking violence and reveals what the Winslows may have done to keep their power intact--and what they might do to anyone who threatens them. Mabel must choose: either expose the ugliness surrounding her and face expulsion from paradise, or keep the family's dark secrets and make Ev's world her own.