Murphy is introduced as a Chicago Police Department officer who leads the Special Investigations (SI) division, which handles cases in which something unexplainable or supernatural is involved. Traditionally SI has been a dumping ground for officers who have made mistakes, and frequently SI officers leave the force. The commander, in particular, usually only lasts a few months. Karrin Murphy is introduced in the first Dresden novel as the Lieutenant of the Division, kicked there for asking too many questions, but too connected to be drummed out of the force.