For much of her life, Sally Holt has been mystified by the things her older sister, Kathy, seems to have been born knowing. Kathy has answers for all of Sally's questions about life, about love, and about Billy Barnes, a rising senior and local basketball star who mans the concession stand at the town pool. The girls have been fascinated by Billy ever since he jumped off the roof in elementary school, but Billy has never shown much interest in them until the summer before Sally begins eighth grade. By then, their mutual infatuation with Billy is one of the few things the increasingly different sisters have in common. Sally spends much of that summer at the pool, watching in confusion and excitement as her sister falls deeper in love with Billy—until a tragedy leaves Sally's life forever intertwined with his.