Mattaku Saikin no Tantei to Kitara

Nagumo Keiichirou was a genius high-school detective. No case was complex enough for him. But what happens to genius detectives when they get older? Now 35, with bad hips, running a failing detective agency with no cases to solve and struggling to pay the rent, he's at a dead end. In comes a high school girl in his office who says she wants to work with him. With her help, will the out-of-touch, old-fashioned Nagumo get back the fire of his youth? --- Alt. Official English: (https://onepeacebooks.com/jt/Tantei.html)