In Jinling in 1936, the winter snow beat on the window lattice like a drum.
When mathematics professor Chen Mobai was found dead in a closed office, with strange ink stains hidden between his fingernails and strange numbers written on his forearm, a revenge trial that began twenty years ago quietly began.
Song Huiyu, a female forensic doctor who just returned from studying in the United States, joined forces with Shen Hetu, a special police detective who walks in the world of light and darkness, to investigate, but found that this was far from a simple murder case. The victim was one of the seven founders of the "Jinling Arithmetic Society". They had participated in a secret "judgment", and now the judge was sending them to the guillotine one by one.
From the secret room of the university to the observatory, to the Qinhuai River engulfed in flames, the killer is closing in step by step, but the clues left behind are like a book from heaven: ancient mathematical symbols, star map coordinates, incomplete chess records and cinnabar ink...
On that day, the Japanese invaders were about to break through North China. This series of cases involving military secrets, astronomical codes and political figures of the Republic of China also dragged seven former friends into the abyss of death one by one.
The key to finding out the truth is hidden in a peculiar hypothesis called the "Ink Blot Theorem" - every drop of ink that seems to be accidentally spilled is a code for a well-planned revenge.
Time is passing and the trial continues.
Who is the real culprit behind this? Who is the next victim?
And who is the woman who was jointly sentenced by seven people?
A deadly game of arithmetic and revenge awaits the final answer.
