One morning, a junior-high student, Kobayashi, wakes up and finds himself in his classroom with his homeroom teacher's body. In his hand is a murder weapon. A high-school detective, Akechi, is called in to assist the police to solve the case.
Kobayashi has been arrested. It seems that he's been charged with additional crimes. Before the police take him away, he whispers something to Hashiba. What will happen to him? Who is the real killer? Will he be able to solve this crime?
Nine girls have been abducted in two months and the police suspect that Shadow-Man, a master of disguise and gentleman thief, might be the kidnapper. When Akechi declines to take part in this case, Kobayashi asks if he can investigate it instead.
A man who calls himself Twenty Faces commits a series of murders. His victims are all criminals who have escaped justice and have not atoned for their crimes. Before he kills, he posts a message on the Internet to explain who he's going to kill and why.
Akechi's chaotic day starts when Kobayashi finds an abandoned kitten at the front door of the Akechi Detective Agency. Kobayashi wants to keep the kitten, but Akechi does not approve. Then another incident occurs. This time, Shadow-Man is involved.
As Kagami predicted, more Twenty Faces have been appearing, ten in the previous month, and now in the current month, the fourth one has just appeared. Akechi and Nakamura head to Panorama Island to inspect the latest crime scene.
Joined by Kobayashi and Hashiba, Akechi solves the crime committed in the exhibition hall on Panorama Island. After coming back from the island, when Kobayashi and Hashiba stop by the office as usual, Akechi starts telling them about his past.
Akechi spends his days and nights trying to figure out the formula that he and Namikoshi created in order to put an end to the Twenty Faces case. Being very curious about the formula, Kobayashi skips school to help Akechi with his work.
The man pulling the strings of the latest Twenty Faces crime was Namikoshi, who everyone thought died three years ago. He starts talking about his junior high school days and how he came to start working on the formula with Akechi.
Namikoshi is trying to change the world using the power of Twenty Faces. Those who are dissatisfied with society gathered to support Namikoshi and his law. What is Namikoshi trying to do? Can Akechi get there before it's too late?
