Students at Keyakizaka Private High School arrive one morning to find their homeroom teacher, Daigoro Tokuyama, dead, and realize the murder occurred that morning; in a panic, they hide his body and decide not to alert the authorities.

The students search for Tokuyama's cell phone after receiving a message from his number and wonder if the murderer has it.

Tokuyama's body disappears and another message arrives; a mysterious woman appears at the school, but seems to be searching for something other than Tokuyama himself.

A new homeroom teacher takes over for the missing Tokuyama and an atmosphere of suspicion descends upon the classroom; a detective arrives to question the students.

The students find something in the air conditioner and wonder who put it there; the detective returns, as does Neru Nagahama; Tokuyama's body begins to stink in the heat.

The students decide to smuggle Tokuyama's body out of the school, but must avoid the security guard and other suspicious figures.