Chased by a gang of criminals, Hofmeister Karl Meixner seeks refuge in a noisy print shop and phones his former superior, Inspector Lohmann Otto Wernicke. He blurts out that he’s uncovered a vast criminal conspiracy, but before he can name its mastermind, disaster strikes: the lights go out, shots echo through the room, and Hofmeister slips into a fever dream of paranoia. When he reemerges, he begins to sing whenever he feels watched, his panic pushing him to a mental collapse that lands him in an asylum overseen by the stern but calculating Professor Baum Oscar Beregi Sr.. The stage is set for a confrontation between madness and a meticulously organized crime, with haunting implications for the city.
In the asylum’s orbit, the enigmatic Dr. Mabuse Rudolf Klein-Rogge is introduced as a mastermind and hypnotist who once spiraled into madness himself. For ten years Mabuse’s influence leaks through the seams of society: a shadowy criminal gang carries out elaborate schemes exactly as “the plans of the Doctor” dictate, though they confide to each other only from behind a curtain. When Baum’s ally, Dr. Kramm Theodor Loos, happens upon how Mabuse’s writings translate into real crimes, he becomes a target of the gang’s execution squad and pays with his life. A cracked glass window at Hofmeister’s crime scene becomes a clue that nudges Inspector Lohmann toward Mabuse, even as Baum insists that Mabuse is dead. Yet Baum’s conversation with Lohmann makes clear a different claim: Mabuse is a genius whose vision could topple a corrupt world.
As the narrative unfolds, Mabuse’s influence surges into action. The Professor, in communion with Mabuse’s ghost, witnesses Mabuse’s voice taking shape in the night sky and merging with the silhouette of his own resolve. A hidden figure coordinates a wave of crimes—poised attacks on a chemical plant, a bank robbery, counterfeiting, poisoning of water, and agricultural sabotage—each step echoing Mabuse’s meticulously crafted “writings.” Among the gang’s ranks, Kent wrestles with loyalty to the criminal enterprise and a growing affection for a young woman named Lilli. Lilli’s plea for honesty nudges Kent toward a confession, one that would push them to the police. But danger closes in when they are abducted and locked in a curtained room that hides a ruthless trap: a loudspeaker conceals a time bomb, and their attempt to escape ends only when they flood the room and break free as the timer detonates.
Meanwhile, the police storm a flat where Hardy Rudolf Schündler and the gang rest between capers, a tense shootout ending in Hardy’s suicide and the gang’s surrender. Bredow testifies that they assassinated Dr. Kramm near the asylum, and Lohmann arranges a tense confrontation between the gang and Baum that yields little in the way of overt justice. Kent and Lilli arrive at the asylum, and Baum’s reaction to Kent sows fresh doubt in Lohmann. Together, Lohmann and Kent press on to uncover the truth behind the night’s events: Baum has become the architect of a plan to strike a chemical plant, and he watches from a distance as the chase intensifies.
The pursuit escalates to the plant, where Baum’s presence is finally exposed. He escapes to the asylum, with Lohmann and Kent in hot pursuit, and Mabuse’s spirit seems to guide Baum toward Hofmeister’s cell. In a final, chilling revelation, Baum reveals himself as Dr. Mabuse, and Hofmeister’s belief in the “genius” behind the crimes is confirmed in a pivotal moment of shattering illusion. Baum makes a last, desperate bid to kill Hofmeister, but guards intervene just as Lohmann and Kent arrive to witness the impossible truth. In the film’s closing tableau, the insane Baum sits in his cell, tearing Mabuse’s writings to shreds, a stark image of the collapse of a grand criminal philosophy and the uneasy triumph of law over the engineered chaos Mabuse crafted.
