A 6-people high school friend group Masaomi, Sho, Runa, Daichi, Hiyori, and Haruto gathered in a luxurious Western-style building after receiving an invitation from the alumni association. They were greeted by a man who seemed to be a butler in the mansion and were pleased to see him again, but no other attendees were found. When they were wondering, a flashy man who seemed to be the owner of the hall appeared, calling himself as a Game Master and told them: "I'm going to ask everyone to play the game. Can I call it "Murder Mystery"? Find out the criminal who killed Inoue Honoka."