In a January 2020 interview with Berliner Zeitung, actress Liv Lisa Fries said that production would likely begin on the fourth season in late 2020 or early 2021. Following a tip off from the Armenian, Gereon listens to a radio broadcast by Dr Schmidt, discussing psychiatric treatment. The National Socialists had turned the country upside down so fundamentally that the Babylonian in Berlin was over. Weintraub and Esther are narrowly saved from assassination when their bodyguard opens a car door and detonates a bomb hidden within. Toni, blaming Charlotte for their sister's blindness, leaves home and leaves a note for Charlotte telling her not to try to find her.

The series is described as the most expensive television drama series in Germany, with a budget of €40 million that increased to €55 million due to reshoots. Babylon Berlin premiered in Germany on 13 October 2017 (Sky 1) and in the United Kingdom and the Republic of Ireland on Sunday, 5 November 2017 (Sky Atlantic).The body of Friedhelm Oelschläger, a civil official, is found in a park with his throat cut; papers found on his body indicate that he was working with Ringvereine gambling operations across Berlin masquerading as legitimate non-profits. In the first season, communists, Soviets and especially Trotskyists play a prominent role (the Soviet ambassador to Germany from 1923 to 1930 was former Trotsky ally Nikolay Krestinsky).

Benda informs Minister Gustav Stresemann of the Black Reichswehr investigation, who is aware and sympathetic to the cause. Inspector Rath is a career Homicide officer from Cologne who inadvertently kills a man because of the adverse publicity his father who is a Senior Police Officer gets his son a transfer to Berlin using connections. Wendt proposes allowing the Nazis to create civil unrest to further the conservatives' plans; the General disagrees.

One example: a police superintendent nicknamed Buddha who weighs 300 lbs and is addicted to gooseberry tarts. Gereon interrogates Johann König, who had been tortured by a mysterious man before the interrogation. Gold and Jacob Grün attempt to meet at a dining club to discuss his kidnapping the women for the Blue Rothschild; they are denied entry as Jews.

Gereon meets with Katelbach and Litten, who are preparing to face trial for exposing the workings of the Black Reichswehr. The first and second seasons, of eight episodes each, were written as one story (covering the first novel of the Kutscher book series) and filmed as one production. The series was co-directed by Tom Tykwer, Hendrik Handloegten [ de], and Achim von Borries, who also wrote the scripts. Abe Gold breaks into Nyssen's castle and forces him to open the safe containing the Blue Rothschild, only to find it missing. Now together, Walter Weintraub and Esther Kasabian visit the grave of her late husband Edgar, "the Armenian," who died the year prior.Benda convinces the Prussian Court to authorise an arrest of Seegers, Beck and other members of the Black Reichswehr. The Gästehaus am Lehnitzsee, a hotel housed in the historic Landhaus Adlon [ de], the pre-WWII mansion of Louis Adlon, manager of the famed Hotel Adlon, was used as the villa of Edgar and Esther Kasabian. While she is at the trial, Toni's friend burglarizes Behnke's boarding house, stealing a set of negatives capable of proving Katelbach's innocence.