A burnt-out detective who peaked at seventeen finally gets a case worth solving, except the case is his own irrelevance. The comedy lands because Nagumo's not trying to recapture youth, he's trying to remember why he ever wanted to be a detective in the first place. A high school girl walks into his office and somehow that becomes the story of a middle-aged man discovering he's not finished yet.

Nagumo Keiichirou once solved the unsolvable. Back in high school, his detective skills were legendary, cracking cases even the police could not. Now thirty-five, with bad hips and a failing agency, he has no cases and can barely cover the rent. Smartphones and modern life leave him baffled. Then Mashiro, an energetic high school girl, bursts into his office and insists on being hired as his assistant. She is set on becoming a detective. He tries to send her away, but she refuses to give up, and she proves her value by teaching him the latest technology and offering a fresh view of his business. Nagumo takes her on, and the old-fashioned veteran and his young assistant start working cases together in a comedic mystery full of generational clashes.