Why is Jesse's behaviour so abberant, while until now, Anna has been so compliant?

Jesse is the oldest child in the Fitzgerald family. After his sister is diagnosed with leukemia as a toddler, he is still a child himself and often has to give up events for Kate. After Anna's birth, he feels useless because he is the sibling that cannot help. He acts out in school and is on a downward spiral into drugs, alcohol, stealing, and arson as he grows up. He tries to project the rebel image around his family, Julia, and Campbell, but his actions show his softer side. He donates platelets to Kate anonymously. He helps Anna out by taking her to the lawyer's office and when visiting Kate. Brian finds out Jesse is the arsonist, and Jesse has a breakthrough. He plays with fire because he can control it. Fire is a theme in the book, and Jesse shows the negative side of fire. He becomes a police officer and wins an award. He transforms himself from a destroyer to a rescuer.