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.