There is something almost horrifying about this story, because it's almost a romantic tragedy, but it has elements of real terror and panic that leave readers questioning if they really have a handle on the story at all. In other words, it's easy to feel that the book is about secrets, and then that the book is about friendship, or love or something, but in the final scene, there is only one real issue left to discuss: paranoia and PTSD. In a sneaky, terrifying way, the whole story is about WWI.
WWI is where David went off to die, the children's first taste of tragedy, but that's not all. Because Robbie was also in the service, he comes back with a disturbed spirit, having witnessed some of the most grotesque human warfare ever in history, but without an analog to process his visions of hell, he is forced to internalize it. When he begins his relationship with Hannah, it feels like the story has turned into a Romeo/Juliet story, but it hasn't. Secretly, in the background, he is desperate for some sort of hope. The biggest secret of all was that Robbie had been left in a paralyzing state of fear and paranoia during a time in history that no one really understood PTSD that well. Hannah thought he felt one way, and Emmeline felt another, but ultimately, he was suffering more severely than he might have the language to express.
Then in the final climax, Hannah shoots him because she knows that he is going to kill Emmeline for what Hannah can tell is nothing but a misguided stunt for attention. But not to Robbie. To Robbie, it's a life or death situation and Emmeline has a gun. She suddenly looks a lot like a war enemy to Robbie whose mind is still on the battlefield, and Hannah is forced to kill him. He was mistaken for his level of intensity, and they could never have guessed he was so shaken. That's the real tragedy of the novel. In a way, although Robbie was not actively suicidal, the implication that he was the kind of person that was liable to commit suicide was so clear to the cast that even the police blindly accept suicide as the cause of death and the real killers get away.
