Los asesinatos de la mansión decagonal, 2

After arriving on the island and settling in the mansion, the members of the mystery club discover several inscriptions among which they have carved the words "Detective" and "Murderer". At first everyone believes that it is a bad joke, but at dawn the next day, they find an inscription hanging on one of the doors that reads: "First victim". To the shock of the group, inside the room they find the body of one of their classmates! Anyone could have committed the murder, and despite the fact that they all seem to have a solid alibi, doubts begin to surface among them... Meanwhile, back on dry land, former mystery club member Kawaminami and Shimada, a private detective, carry out an investigation. investigation of the homicide that took place six months ago on the island. However, when it seems that they are one step closer to solving the case, they both receive a letter from Seiji Nakamura, the owner of the mansion who was thought dead!