Shugo Hayami is a doctor at a nursing hospital, which was once a psychiatric hospital. One evening, when Shugo is on night duty, a man in pierrot mask breaks into the hospital and he is not alone. He is with Hitomi Kawasaki, a university student who has been shot by the masked man. The masked man tells Shugo to treat Hitomi. He also takes hostage the 64 people in the hospital. Soon, Shugo and Hitomi try to escape from the hospital and they encounter mysterious cases one at a time.
On-call substitute doctor Shugo finds himself faced with a terrifying criminal in a clown mask. The assailant demands that Shugo treat injured high school student Hitomi. The perpetrator sets siege to the building.