Gwen Castle's Biggest Mistake Ever, Cassidy Somers, is slumming it as a yard boy on her idyllic Nantucket-esque island this summer. He's a rich kid from across the bridge in Stony Bay, and she hails from a family of fishermen and housecleaners who keep the island's summer people happy. Gwen worries a life of cleaning houses will be her fate too, but just when it looks like she'll never escape her past - or the island - Gwen's dad gives her some shocking advice. Sparks fly and secret histories unspool as Gwen spends a gorgeous, restless summer struggling to resolve what she thought was true - about the place she lives, the people she loves, and even herself - with what really is.