Alumni of a renowned high school's golf club gather to bid farewell to their retiring adviser. During the event, houseman Hirayama Yuta falls from a terrace into the sea. Detectives Nihei Jiro and Miyama Chiaki investigate, initially deeming it an accident. Mysterious Director Ouga Toichi arrives, suspecting foul play and starts a discreet investigation. Ouga coerces Nihei and Chiaki to join. Evidence mounts against the accident theory, especially when student Okumura Aoi, who had conflicts with Yuta, emerges. Ouga, determined to find the truth, uncovers threats and attacks targeting alumni. The trio suspects a serial murderer targeting the golf club graduates, possibly orchestrated by a mastermind known as the Joker.