The books cleverly use his job title and postings as mile markers. He begins as a Probationary Warden, gets moved around, faces disciplinary hearings, and eventually earns a senior position. But it's the subtler changes that impressed me: his crime scene assessments become more thorough, his interviews more insightful, and his understanding of wildlife forensics becomes a major tool. He transitions from reacting to events to anticipating them.
His relationship with his superiors, especially his mentor Sgt. Kathy Frost, is a great barometer. Early on, he disobeys her constantly. Over time, their dynamic shifts to one of mutual respect and strategic partnership. You can track his maturity by how often he picks up the phone to consult with her versus how often he charges off alone. The order is essential because each book's climax often teaches him a specific lesson that alters his behavior in the next installment's first chapter.