In this episode, the investigation into the murder at Nandan Observatory continues. Totomaru and Ron, who were previously suspected, are now working to find the real culprit. The setting remains the observatory with its various facilities and the surrounding island.

At the beginning of the episode, Totomaru examines the observatory's dome and discovers bullet holes in the lamps, suggesting they were shot out with a firearm. This discovery is crucial as it contradicts the assumption that Ron could be the shooter, since he is known to be unable to handle guns.

The guests and employees of the observatory are reintroduced, each with their own alibi for the time of the murder. Among them are Jumonji, the observatory director; Donzawa, a guest; Unno, the cook; and Orihime, an idol. Their alibis are checked, but none conclusively point to the murderer.

Although Ron is initially suspected, his innocence is proven when Totomaru discovers that the lights in the dome were turned off before Ron could enter, as evidenced by the absence of glass shards on Ron's bare feet. With this revelation, the focus of the investigation shifts.

The episode takes a dramatic turn with the murder of John Grizzly, Ron's former superior and instructor at the BLUE Detective Academy. This second murder complicates the mystery further, as it occurs on the same remote island, now cut off from the police due to a typhoon.

Ron and Totomaru deepen their investigation, examining the scenario of the first murder in a locked room and the circumstances of Grizzly's death. They consider various methods the killer might have used, including fishing lines and the observatory's equipment.

The episode ends with Ron and Totomaru piecing together the clues, including the use of the fishing line and the positions of the victims. Ron declares that he has solved the mystery of the locked room and is close to identifying the murderer. The episode concludes with a cliffhanger, paving the way for further revelations in the next installment.