A professional or amateur detective solves a mystery in a detective book, a type of fiction. The mystery could involve a single murder, a string of killings, or even an unsolved crime. Typically, the investigator is motivated to solve the case for personal reasons like retribution or atonement. The detective novels is often shown as smart, knowledgeable about investigative techniques, and frequently assisted by assistants who provide additional expertise. Typically, the detective either exposes or punishes the criminal at the conclusion of the investigation.