David is feeling pretty ho-hum about life when we first meet him. Then, all of a sudden, he runs into Melanie. She ignites his interest (oh, and sense of lust, too) and he finds something to be passionate about.
David invites Melanie to his place and the whole intrigue begins. Once they start having sex, things seem like they can't get much better for him. He finds the passion that has been lacking in his life, and for a while he's on top of the world.
Ryan, Melanie's boyfriend, shows up, telling David that what he's done is wrong. Soon, the whole University is abuzz. Melanie files a complaint against David, who can't believe what is happening. Things get out of control and he loses his job. His colleagues are totally dismayed with him. He's knocked from his pedestal and has to go stay with Lucy to lie low for a while.
Without any previous warning, Lucy and David encounter the three intruders out on a walk one day, and when they return home they're there waiting for them. In a scene of unbelievable violence and ruthlessness, Lucy and David have their worlds turned completely upside-down. Even after the attack is over, it continues to inform and influence their relationships (particularly with one another), their habits, and their future plans. Life can't go on as before.
Luckily for David, he doesn't actually die at the end of the novel. With a twist on the traditional tragic ending, someone else dies in his place: the dog with the bad leg. Rather than keeping the dog alive to wallow in its disgrace, David decides to let Bev put it out of its misery. Allowing the dog to stop living in shame is a symbolic gesture through which David appears to begin a new chapter of his own life.