Fourteen-year-old Nikki Simons has lost her mother to cancer. Her older sister, Bonnie, will soon be off on an exciting trip before heading to college, leaving Nikki to cope with things at home, including her little brother, Sam.
Nikki still grieves for her mother, knows she will desperately miss Bonnie, and feels inadequate to fill in for them at home. And then their father makes a shattering announcement: He is going to marry Crystal, a woman he met through work who is only slightly older than his daughters.
Not long after the peculiar wedding (none of Crystal's family or friends attended), Nikki learns that in place of a European trip the family had planned before her mother's death, they will be spending part of the summer in the village of Trinidad, in northern California, where Crystal has inherited a house on the beach.
Nikki decides that going to the beach is preferable to having no vacation at all. But soon she's troubled by more than just Dad's hasty marriage to a woman who doesn't make much of an attempt to relate to his children. Other things about Nikki's new stepmother remain unexplained: Why is she reluctant to return to the house where she spent some time as a child? And after Dad is called back to Seattle on an emergency, what awful secret causes Crystal to have nightmares that waken Nikki out of a sound sleep? How is Nikki, by herself, expected to cope with things that baffle and frighten her?
Then Nikki meets Julian Gyasi, an intriguing boy known as Spook who lives in a house on the cliff nearby. Why are there mysterious lights in the tower windows over there, and who is the man who frightens Nikki by watching her from the top of the cliff? As the days pass, Crystal's behavior becomes even stranger and Dad is still not there to help Nikki deal with either her stepmother or the increasingly mysterious situation at the Gyasi house.