Keiichiro Nagumo may have been a super great detective at one point, but now that he’s in his thirties, he’s just some dude. Appearing before this outmoded private eye is Mashiro, a high school girl brimming with youth, and the pair tackles cases together as they contemplate their generation gap. Until one day, a rival (?!) detective comes to them with an SOS.

Behold, a great detective who thrills the world solving impossible cases in no time! His name? Keiichiro Nagumo.
…But all of that was over a decade ago. Now he’s just your typical middle-aged dude. Nagumo is behind the times to the point that he doesn't even know what a smartphone is. But out of the blue, he is confronted by a high school girl named Mashiro who shows up wanting to be his assistant. Witness the miracles a gender-gap detective duo can make!