Loyalty
Loyalty is a major theme in this novel. All four of the main characters are fiercely loyal to each other: with no questions asked, they throw away their phones and run away from their homes in order to protect Jamie. Olivia has a strong bond with Jamie, and their loyalty is boundless. Beth Hunter is also loyal to Lillian, helping her daughter when she's in trouble. Loyalty is at the core of the plot: it's the loyalty of the four friends against the treacherous disloyalty of others, such as Steven, Vicky, and Louis.
Mental Illness
Lillian struggled with mental illness while she was alive, and she eventually committed suicide on her eighteenth birthday by walking into a river. Olivia, her daughter, seems to have inherited a little of this trait. She struggles with letting go and giving in to the desire to just stay underwater - the serene, impersonal scene feels so natural to her. Other aspects of her thought process, especially after Jamie's death, reflect mental illness; her behavior is strange, reflective, and erratic, and by the end of the novel she has agreed to regularly see a psychiatrist.
Parental Problems
This novel is full of characters who have problems with their parents: the only one who doesn't, actually, is Max. Olivia's parental situation is terrible: her mother committed suicide after Olivia was born, and her father won't take her in because she reminds him too much of his mistakes with Lillian. Jamie's situation is, if possible, even worse: his father is an abusive alcoholic, and he beats up his wife which Jamie watches several times a week, leading to Jamie trying to spend as much time at Olivia's house as possible. Maggie even has parental troubles: her mother is a struggling folk artist/drug addict, and her father is out of the picture. Maggie's mother sells them out, and Jamie and his father both end up dead, but Olivia reunites with her dad at the end of the novel, showing at least one example of reconciliation.
