Shinpei first meets Kasumi at a movie theatre, in a certain way an impressive encounter as he wrongly sits in her seat. The path of the two cross again as Kasumi later becomes Shinpei’s co-worker at a restaurant. One night, Shinpei finds Kasumi acting suspiciously in front of a building. She is stalking her boyfriend, whom she suspects cheated on her. Knowing the secret, Shinpei is asked to lend a hand in the infidelity investigation. Their nights then turn into a detective game and Shinpei finds himself drawn to the charm of Kasumi...