A group of friends who have known each other for many years and are all keen swimmers often holiday together to enjoy open water swims. But now they have gathered on a remote island for a memorial service for Lissa who is believed to have drowned while swimming alone at night. Georgie cannot understand how this could have happened and unsettles the others with her questioning of the events surrounding her best friends death. The story explores the relationships between the friends and gradually builds up a picture of Lissa. They all have secrets which eventually are revealed. The island which at first seems idyllic becomes a place to escape from as lives are threatened and no one feels safe. There are several twists in the plot but parts are rather strange especially the frequent references to a mysterious sea serpent which may or may not be real.