For twelve hours each day, the Scottish island of Eris is cut off from the mainland. No way in. No way out. The island’s only house was once home to Vanessa, whose notoriously unfaithful husband disappeared twenty years ago. But Vanessa is dead now, and her friend Grace has moved in. A solitary creature of the tides, content in her own isolation, guarding the island’s past. . . Meanwhile, in London, a stranger makes a small but terrible discovery - a human bone. And in that moment Grace’s precious solitude is threatened. How will she respond? Can she be trusted? The secrets of Eris Island won’t stay buried for long. And suddenly this is a very dangerous time to be alone . . .