Shen Mo, a genius forensic consultant who acted in a gray area during his lifetime, was sentenced to the animal realm due to his sins after his death. Coinciding with the modernization and reform of the underworld, he relied on his top criminal investigation and autopsy skills to sign a "sale contract" with the King of Hell and became a temporary worker in the Underworld's Cold Case Review Department. His mission is to overturn the verdicts of the souls who are stranded in hell and whose grievances have not been resolved, so as to accumulate merit and offset their previous sins. Shen Mo, who was forced to go into business, was forced to listen to the cries of the dead souls and explore the mystery of the Yin and Yang worlds. However, when he peeled off the cocoon and avenged an old case, he discovered that his death, the truth about his sister's early death, and even a huge shadow running deep in the underworld were vaguely pointing to him... This is a journey that begins with commutation and ends with redemption. A sinner will seek justice for all living beings in the underworld, and also find an answer for himself.
