Mark is sick. He decides to run away to deal with it on his own terms, to not have to watch his family and friends deal with his sickness again. It's a decision I would respect from a grown-up, but not from a kid. Maybe I'm too judgmental, I don't know. The story alternates between his perspective and his friend Jessie, who knows what he has done and has to decide whether or not to tell. I definitely felt for Mark, but perhaps since I'm an adult, I felt way more for his parents.