Harvard 1960. Nineteen-year-old Susannah says farewell to college life for the summer and returns to Vinalhaven Island, her remote rocky home off the coast of Maine. Her beloved sister Kate is marrying Matthew, a local fisherman, a man with a heart as cold as the Atlantic Ocean.

Years later, nurse Emer is sent to Vinalhaven to look after Susannah, who has lived in isolation since her sister’s tragic death. When Emer discovers a bundle of letters in a rainbow quilt in the bedroom, she and Susannah grow closer. Eventually, Susannah opens up enough to tell Emer the story of Kate’s brutal and secret past.

But when Emer starts asking locals about Kate, the island air sizzles with hostility. There are people who would rather that Susannah kept quiet, who have no qualms about threatening Emer. But despite the warnings to stay away, Emer is determined to find out what really happened the night Kate died – and the final secret that is keeping Susannah a prisoner to the past.