Sorrow of the Fatalist is the 5th chapter of Bungo Stray Dogs.
Atsushi is worried about the Agency getting attacked by the Port Mafia because of his bounty, so he decides to leave the Agency in hopes of keeping everyone safe. Despite that, the Agency is still attacked by a special Mafia combat group called the Black Lizard. Atsushi, hearing of this, hurries back, but discovers that there was nothing to fear since the Agency easily dispatches the Black Lizard. After the incident, Ranpo announces that he was asked to solve a murder case. Atsushi is told to go with him.