The time is the early Showa era.
A letter arrived at the Mikage office.
A series of murders that occurred in the Sakaki and Hirunuma families.
The investigation comes to an end without the truth being solved.
A request arrives to uncover the truth of the case.
However, the sender is a person named Hazuki Hirunuma, who should have died 15 years ago.
Mystery begets mystery, and Mikage Fukuro takes on the challenge as an armchair detective.