Takashi Shimizu's newest film is about a mysterious cassette tape containing a melody. People who hear this melody gradually begin to hum it themselves and become involved in a mysterious incident. What is the mystery behind this melody ?

During the summer vacation period, temporary teacher Honoka Kimijima is in charge of a supplementary class. One day, a female student suddenly jumps off from the school rooftop and dies in front of Honoka Kimijima. Then she notices a mystery student who is not supposed to be there.