After the Mystery Club arrives on Tsunojima Island, they discover mysterious tablets with things like "Detective" and "Murderer" written on them. They initially see it as a tasteless prank, but when the roles written on the tablets start to come true, and the victims begin to pile up, the group realizes their lives will depend on finding the killer...
Meanwhile, on the mainland, Kawaminami and Shimada are chasing after the truth behind the "mysterious quadruple homicide"...