The 21-year-old college detective, Souma Reiko, met a young police officer named Aoyama Zuo while solving a case. Because of their similar age and similar interests, the two quickly became good friends. With the help of Ari Soma Reiko, Aoyama Sa's career is booming, but he doesn't know that their meeting was planned. By chance, Aoyama Zuo discovered clues and followed the clues, discovering a mysterious organization called "Letter". . . . . . .