For twenty years Kayla, Antoinette, and Val have performed their own special summer ritual. Once a year the old friends put aside their daily, separate lives to drink champagne, swap stories, and swim naked under the Nantucket stars. But on one of those bonding nights, one of them swims out from shore and doesn't return. After the surviving friends emerge from their grief, they realize that the repercussions of their loss go far beyond their little circle, and they begin to uncover layers of secrets - and their connections to one another - that were never revealed on the beach. What has made their friendship strong now has the power to destroy - their marriages, their families, and even themselves.