Vanessa Sands returns to Winter Harbor to find out why her sister Justine leaped to her death. When Vanessa learns that Justine's boyfriend Caleb is missing too, she and Caleb's older brother Simon join forces to find him. As Vanessa and Simon spend time together, their relationship grows from childhood friendship to something more.
Winter Harbor is abuzz with anxiety when another body washes ashore, and panic sets in when the small town becomes home to a string of fatal, water-related accidents. The phenomenon hits close to home with Vanessa. The deaths bring to the surface the root of her fears, and a secret she's kept for years. As the bodycount mounts, Vanessa begins to understand that she is a siren.