The home of the wealthy Mitarai family, which has run a hospital for generations, was burned to the ground in an unfortunate fire. Thirteen years later, housekeeper Anzu Murata heads to the home of her new client, the Mitarais. There, she is greeted by the beautiful and impeccable second wife of Mrs. Mitarai, Makiko. Anzu is hired and begins working at the house, but she has a certain purpose for infiltrating the Mitarai home...
With graduation 10 days away, homeroom teacher Hiiragi gathered all 29 students of class 3-A and proclaims them his hostages. His last lesson regards the death of a student that passed away a few months before. Nobody will be able to graduate until the truth is known.