The closed circle of suspects is a common element of detective fiction, wherein a given crime occurs within a limited and predefined group of characters, all of whom are isolated in a confined setting such as a remote estate, island, or train, ensuring the perpetrator must be one among them. This narrows the investigative focus to a limited number of suspects, each with credible means, motive, and opportunity. The detective has to solve the crime, figuring out the criminal from this pool of suspects, rather than searching for an entirely unknown perpetrator. The subgenre that employs this can be referred to as the closed circle mystery. Less precisely, this subgenre – works with the closed circle literary device – is simply known as the "classic", "traditional" or "cozy" detective fiction.