A magazine publicist investigates an unsolved murder case that occurs on Halloween every year.

High school student Nanami lives in Tokyo, Japan. She waits for Halloween because she enjoys dressing up in costumes with her friends. One day, Nanami’s father tells her about a mysterious serial murder case that takes place year on Halloween. Her father works as the chief editor at an occult magazine. At first, Nanami doesn't care about the serial murders, but frightening incidents keep taking place around her.