A mystery film is a film that revolves around the solution of a problem or a crime. It focuses on the efforts of the detective, private investigator or amateur sleuth to solve the mysterious circumstances of an issue by means of clues, investigation, and clever deduction. Mystery films include, but are not limited to, films in the genre of detective fiction.

A private investigator, a private detective, or inquiry agent is a person who can be hired by individuals or groups to undertake investigatory law services. Private investigators often work for attorneys in civil and criminal cases.