Episode 40

The Secret Founding of the Detective Agency (探偵社設立秘話,) is the 40th episode of Bungo Stray Dogs anime series and the third episode of the fourth season. It aired on January 18, 2023.

Summary
Apparently en route to the police station, Mitamura praises Ranpo's deduction skills and Fukuzawa's prowess in solving the recent case. However, Ranpo claims that Mitamura still doubts him possessing an ability, so he offers to answer the cop's questions until he runs out of queries to prove that he is truly gifted. As a start, Ranpo correctly deduces that they are not heading to the police station, which Mitamura dismisses can be easily observed.

Ranpo then urges him to ask anything related to the recent incident, to which Mitamura asks how the suited man restrained in the theater was captured. The detective reveals that someone abducted the man using a rug and organic solvent, whom Mitamura guesses must be the playwright Kurahashi, but Ranpo states that the latter must have been already killed even before the performance. He also points out that the entire project is an elaborate ploy all to abduct the suited man, afterwards slyly calling out Mitamura for reeking of organic solvent.

At the theater, Fukuzawa grows wary that the case is not yet over, especially upon learning that there have been no confirmed reports of Ranpo and Mitamura arriving at the station, the police cannot connect to the vehicle's radio, and Mitamura cannot be contacted. He tries to piece together the information he has, from Kurahashi's death to Murakami being only used as the "shrimp" used to catch the "sea bream" as Ranpo previously hinted to Egawa. He then sets out to look for Ranpo, during which he spots a message hidden by the boy stating that Mitamura is the perpetrator and to look for the suited man's cane.

Mitamura and Ranpo arrive at V's hideout by the harbor, while Fukuzawa finds the cane which he finds out to be a contraption of sorts. Ranpo deduces five soldiers on guard outside, whom Mitamura reveals to be initially after the suited man. With their scheme derailed at the theater, he becomes tasked to catch and interrogate the detective who ruined their plot. To avoid using force, Mitamura invites Ranpo to work with them, ability users alike, in ridding the country of fellow ability users, though Ranpo displays uninterest.

With assistance, Fukuzawa visits Oda in his cell and asks whether he has been recently hired, possibly by the organization V, to capture the suited man whom Fukuzawa deduces is an ability user under a high-priority witness protection program, based on the device he found in the cane. Initially reluctant to talk, Oda soon reveals that V indiscriminately kills as a ritual, much to Fukuzawa's unrest. The latter, bent on saving Ranpo, offers to testify for Oda's release in exchange for information; moved by Fukuzawa's willingness to bend justice for his subordinate's sake, Oda accepts his proposal and requests to give him some curry instead in exchange for intel.

Mitamura continues his attempts to persuade Ranpo into joining them, but Ranpo still shows uninterest towards their cause and even ridicules the man's ramblings. Provoked, Mitamura draws and points his gun at Ranpo, who in turn counts down three seconds. Just as predicted, Fukuzawa arrives and knocks out Mitamura and the five guards. Ranpo then voices out his glee after accurately calculating Fukuzawa's arrival, but the latter slaps and reprimands him for risking his life in the name of his deduction. Tearing up, Ranpo embraces Fukuzawa and repeatedly apologizes.

The next morning, Fukuzawa discovers from the news that Mitamura has been killed while in custody, an act Ranpo deduces must have been to silence the man. As Fukuzawa wonders who V might be, Fyodor Dostoevsky blithely mutters to himself from a distance that V actually refers to "Five", whose presence Fukuzawa grows alarmed of. Ranpo then notes how the city seems different than before, which Fukuzawa attributes to him now being able to understand what is important. Meanwhile, Oda receives some curry in his cell and enjoys its spice.

In the post-credits scene, Fukuzawa and Ranpo arrive at the Bankoudou Hall, where they are welcomed by the suited man; Ranpo figures out that the man saw through the trap during the play and allowed capture to pave way for the duo to catch the perpetrators. Fukuzawa then seeks help from the man, Sōseki Natsume, in securing a Skilled Business Permit for a business he intends to establish where Ranpo can operate as a gifted detective. Natsume, despite reminding them of the challenges they shall face along the way, places his faith in the two, marking the steps towards the origins of the Armed Detective Agency.