A 16-year-old high school student Midori Matsumoto was found dead on the banks of the Tama River. The only clue is shoe marks on rubber soles. From the interview of witnesses, it became clear that Midori was walking with a guy last night. In addition, it turned out that Midori was close to a college student Kimoto, and a high school student Miyazaki. According to his friends, Miyazaki had an alibi, but Kimoto did not. A unique work in which the problems of teenage sex are considered from the point of view of the murder of a girl. The 21nd work from the popular series "Keishicho Monogatari", which documents the activities of the First Investigation Division of the Capital Police Department.