Bodyguard-for-hire Yukichi Fukuzawa reluctantly takes on the arrogant boy genius Ranpo Edogawa after their paths cross in Yokohama, and their first case together involves a death threat against a theater troupe. Solving it convinces Fukuzawa that Ranpo's deductions are worth keeping around permanently, setting the stage for what will become the Armed Detective Agency. This ongoing prequel manga traces the agency's earliest days, before Dazai, Atsushi, or any of its later members join.