A group of old university friends travel to Unst to celebrate the marriage of one of their friends to a Shetlander. But late on the night of the wedding party, one of them, Eleanor, disappears. The following day, Eleanor's friend Polly receives an email. It appears to be a suicide note. And then Eleanor's body is discovered, lying in a small loch close to the cliff edge. Detectives Jimmy Perez and Willow Reeves are dispatched to investigate. Before she went missing, Eleanor claimed to have seen a ghost. Her interest in a ghost had seemed unhealthy to her friends. But Jimmy and Willow are convinced that there is more to Eleanor's death than they first thought.