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. Now this remote and beautiful place is home to Grace . . . a solitary creature of the tides, guarding the island?s past. But far away in London, a stranger has just made a startling discovery - a human bone where no human bone should be. And in that moment Grace?s precious isolation is threatened. How will she respond? Can she be trusted? Or is it Grace who should be afraid?