Driven out from his orphanage, Nakajima Atsushi wanders the streets of Yokohama on the bring of starvation. Determined to live, a chance encounter with a drowning stranger changes his fate...

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...

In the aftermath of Atsushi and Dazai's abduction, the Agency must decide what to do with Kyouka, the loose end. Meanwhile, the Port Mafia also deliberates what to do with Akutagawa, now comatose, as his enemies seek vengeance...

The leaders of the Agency and the Port Mafia negotiate an alliance. Meanwhile, Dazai and Chuuya face off against Lovecraft.

The Detective Agency president is in safe hands for now, but unless he or the Port Mafia boss dies, a full-scale war between the two organizations is inevitable.