Her mother's third marriage is only hours old when all hope for Clare's fifteenth summer fades. Before she knows it, Clare is whisked away to some ancient cottage on a tiny marsh island on Cape Cod to spend the summer with her father—a man she hasn't seen since she was three. Clare's biological father barely talks, and when he does, he obsesses about endangered turtles. The first teenager Clare meets on the Cape confirms that her father is known as the town crazy person. But there's something undeniably magical about the marsh and the island—a connection to Clare's past that runs deeper than memory. Even her father's beloved turtles hold unexpected surprises. As Clare's father begins to reveal more about himself and his own struggle, Clare's summer becomes less of an exile and more of a return.