Mystery fiction is a  genre of fiction usually involving a mysterious death or a crime to be solved. In a closed circle of suspects, each suspect must have a credible motive and a reasonable opportunity for committing the crime. The central character must be a detective who eventually solves the mystery by logical deduction from facts fairly presented to the reader. Sometimes mystery books are nonfictional. "Mystery fiction" can be detective stories in which the emphasis is on the puzzle or suspense element and its logical solution such as a whodunit. Mystery fiction can be contrasted with hardboiled detective stories, which focus on action and gritty realism.