Mysterious mass deaths are occurring frequently in different parts of the city, with a common factor being the timing of their discovery. Sasaki, a trainee doctor, becomes embroiled in one of these tragic events, finding himself trapped in a dungeon ruled by a cannibalistic creature called "Hitokui." With other victims being preyed upon and devoured in his presence, Sasaki must find a way to escape and put an end to the series of mass killings.