Greg and Tess MacAvoy are one of four prominent Nantucket couples who count each other as best friends. As pillars of their close-knit community, the MacAvoys, Kapenashes, Drakes, and Wheelers are important to their friends and neighbors, and especially to each other. But just before the beginning of another idyllic summer, Greg and Tess are killed when their boat capsizes during an anniversary sail. As the warm weather approaches and the island mourns their loss, nothing can prepare the MacAvoys closest friends for what will be revealed.