The episode begins with Totomaru and Ron arriving on a remote island to observe a meteor shower at the Nandan Observatory. The island is known for its sugarcane and black sugar syrup. The observatory, an important location, is introduced with its various facilities, including a lobby with a replica gun, guest rooms, and an observation dome.

The guests at the observatory are various individuals who share a common interest in astronomy. Among them are Onodera, a photographer of celestial objects, Orihime, an idol and astronomy enthusiast, and John Grizzly, an instructor at the BLUE Detective Academy and Ron's former superior. The director of the observatory recounts the tragic history of the place: Ten years ago, during a similar meteor shower, seven people, including the director's father, were killed in a shooting incident, a case that remains unsolved to this day.

As the evening progresses, the guests enjoy the buffet and await the meteor shower. Ron, known for his eccentricity, drinks black sugar syrup and dances with a hula hoop, drawing the attention and amusement of the guests. The mood is lively until a gunshot rings out from the observation dome.

When the guests investigate, they find Onodera dead and Ron unconscious in the dome, which was locked from the inside, creating the perfect locked-room mystery. A key to the dome is found in Ron's pocket, and the replica gun from the lobby, now missing, is suspected to be the murder weapon. Despite Ron's initial silence, he eventually reveals a crucial detail: He cannot handle firearms, casting doubt on his guilt.

The episode delves into Ron's troubled past, revealing an incident five years prior where he was found with the corpses of seven murderers, leading to his expulsion from the detective academy. Although the evidence seems to point to him, Ron's inability to handle weapons and his past trauma suggest that he cannot be the culprit.