Toto and Ron accept an invitation to the observatory. Ten years ago, a gruesome mass murder took place here. Director Jumonji, the photographer Onodera, the instructor John Grizzly, the idol Orihime, and others are introduced. Onodera, who specializes in astrophotography, is found shot dead inside a locked dome. John Grizzly, a respected instructor, is shot on the observatory's roof and falls to his death.

Toto and Ron investigate the murders. Toto accuses the present director, Jumonji, of being the killer. Toto explains the mystery of the locked room and the method of the murders, which involves an elaborate setup using a rifle, a fishing line, and the observatory's telescope.

Jumonji confesses to the murders and reveals his motives, which are tied to a crime from decades ago and his desire to cover up his father's misdeeds. As Ron pressures Jumonji, he attempts to take his own life with poison. Ron reflects on the similarities between this case and his past, suspecting a deeper conspiracy against him. It turns out that Jumonji faked his death with the help of the criminal underworld organization "House of M."

Ron realizes the extent of the conspiracy against him and decides to conduct further investigations to uncover the truth about his past and the current case. The episode ends with Ron and Toto leaving the island to ponder the secrets and their future.