A man named "M" invites seven people to a murder game party. Among the eight in the room, one will become a victim, and another the culprit.

A man who introduces himself as K's old friend offers the detectives lavish pay and a chance to partake in a special mission -- but there's a catch.

A culprit asks specifically for the detectives to escort him to the police station. In exchange, he promises to tell them everything they want to know.