[3] In addition to the central mystery, Yokomizo uses the story to illuminate the traditions, customs, and agrarian rhythm of rural Japan in the early twentieth century as well as anxieties about changing class distinctions.

[4] The omniscient narrator, in an aside to the "Gentle reader," explains that the word "lineage, which has all but fallen out of usage in the city, is even today alive and well in rural villages like this one," and the killer's motive is revealed to relate to an obsession with traditional concepts of honor and family bloodlines.

The anonymous narrator reconstructs the events surrounding the legendary double murder of a married couple, based on witness statements and various documents.

Early in the morning after the wedding night, screams and then the music of a koto are heard from the family's nearby annexe, which was intended for the newly married couple.

A Japanese sword is later found thrust into the ground in the middle of the garden, with no footprints on the surrounding thick snow, creating a perfect locked room mystery.

Finally, the youngest daughter of the family, Suzuko, claims to have seen the Three-fingered man in the garden the day after the murders when she went to visit her cat's grave.

Kindaichi finds a severed hand with three fingers in the grave of Suzuko's beloved cat and a little later the body of the Three-fingered man with a large wound in the chest in a charcoal oven near the estate.

When he learned that his fiancée was no longer virgin, but that he could not dissolve the marriage without losing his face, he decided to kill her and then himself, making the act look like a double murder.

Originally, Kenzo had planned to suggest the perpetrator's escape through the window, but since he forgot to open it, the murder seemed like an impossible crime.

After catching his brother preparing the mechanism, he became involved and decided to help him - on the one hand to get part of the life insurance, on the other to satisfy his urge for superiority as it is revealed he may be a psychopath.

The crucial mechanism, according to Kindaichi, was probably inspired by the one in the Sherlock Holmes short story "The Riddle of Thor Bridge", in which a similar concept is used to make a suicide look like a murder.