Despite joining the Armed Detective Agency, Nakajima lacks conviction that he'd be of any use. Just as he's about to bid the agency farewell, a bomber takes over the agency with one of the agency employees as his hostage...!

Though saved from the Port Mafia by Dazai's intervention, Atsushi feels responsible for bringing trouble to the Agency's door. Rather than risk another attack because of him, Atsushi decides to leave the Agency and makes a call to the Port Mafia...