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.

When seventeen-year-old Vanessa reunites with her biological mother, she faces the dilemma of a siren's existence, that in order to survive she must endanger the lives of those she loves most.