[Machine Translation] A boy who had been bullied came to junior high school wearing a mask. Then, he changed into a cheerful personality as if he had become a different person! It became news, and the masks went viral in schools all over the country! However, a murder occurs... Ariki and Mitsugi sneak into the masked assembly and investigate the conspiracy hidden behind it. Our Eiji and Aihara and the others cooperate with the investigation! This is the third installment of Osamu Soda's Mystery 2A Detective Bureau. From elementary school upper grade.