Each summer the wealthy, seemingly perfect Sinclair family meets on their private island. Cadence, Johnny, Mirren, and Gat are a unit, especially during "summer 15," marking their fifteenth year on Beechwood-- the summer that Cady and Gat fall in love. Cady became involved in a mysterious accident, in which she sustained a blow to the head, and now suffers from debilitating migraines and memory loss. When she returns to Beechwood during summer 17...

"It used to be that Belly counted the days until summer, until she was back at Cousins Beach with Conrad and Jeremiah. But not this year. Not after Susannah got sick again and Conrad stopped caring. Everything that was right and good has fallen apart, leaving Belly wishing summer would never come. But when Jeremiah calls saying Conrad has disappeared, Belly knows what she must do to make things right again. And it can only happen back at the beach...