In the autopsy room of UDI (Unnatural Causes Research Institute), forensic doctor Mikoto Misumi is working intently.This institute specializes in receiving the remains of those who died in abnormal conditions or died of homicide. It processes about 400 remains every year, with the purpose of finding out the true cause of death for the deceased.UDI has two main teams - the Misumi class and the Nakado class, each dedicated to solving the mystery of the cause of death.

A couple walked into UDI, unable to accept the verdict that their son, Takano Shima Watari, had died of asthenic heart disease.They firmly believed that there was something strange about the cause of their son's death, so they entrusted UDI to find out the truth.Misumi Mikoto took over the case, and she decided to start with the autopsy of the body to find out the real cause of Takanoshima Watari's death.

After careful dissection, Mikoto found that there was no abnormality in Takano Shimawatari's heart, but there were symptoms of acute renal insufficiency.She suspected the death may have been caused by poison.At this time, a colleague of Takanoshima Watari also died suddenly. The cause of death is unknown.Is there some connection between the two deaths?

Mikoto and her team began to investigate in depth, and they met Takanoshima Wataru's fiancée Baba Riko.Luzi revealed that she was developing a highly toxic drug called “Anonymous Poison”.The drug may have been linked to Koyashima's death.The racecourse insisted that she was home alone at the time of the incident and had no alibi.