From Goodreads: "Nothing has been the same for Will ever since what happened last summer. One day, on an ordinary sailing trip with his brother, there is a strange accident. When Will wakes up, he learns his brother has disappeared, presumed drowned. Worst of all, Will can't remember what happened—his family finds him unconscious, with no memory of the accident.
Now Will and his best friend and neighbor, Gretchen, are starting a new summer. Gretchen seems troubled—her sleepwalking habit is getting worse, and she keeps waking up closer and closer to the water. Will is drawn to Asia, the exotic new girl in town. Nobody knows where she's from—all Will knows is that her beauty and her mesmerizing voice have a powerful effect on people.
Then there is another mysterious drowning, and Will and Gretchen begin to wonder: Is Asia just another beautiful, wealthy summer resident? Or is she something entirely more sinister . . . and inhuman?"