The Testament of Dr. Mabuse is the sort of film that deserves, if not a critical reappraisal (does anyone actually dislike it?), then at least a rediscovery. Fritz Lang's follow-up to M follows similar themes using similar techniques on a much grander scale. Though this is accurate, I'm afraid it will make Mabuse look like the Casino to M's Goodfellas. Mabuse is a masterpiece, every bit the equal of M. Lang refines his use of sound to make far greater statements than simply suggesting the presence of evil.
M was unique for presenting a number of undeveloped characters surrounding Peter Lorre's Hans Beckert. The only character we knew there was Becker, making him, a child murderer, the audience surrogate by the film's end. Mabuse works in a completely opposite manner, giving us numerous protagonists surrounding a barely developed central villain. We primarily follow Tom Kent (Gustav Diessl) and Inspector Lohmann (Otto Wernicke, reprising his role from M) as the former works within Mabuse's criminal organization and the latter works to investigate why an informant (Karl Meixner) has gone insane. Tom eventually refuses to commit murder for the organization, leading to a direct conversation with Mabuse, literally the man behind the curtain. Here is where Lang's film goes from being a well-crafted thriller to flat out masterpiece.
This is the second film Lang made in the sound era, and it continues his fascination with the new technology. In M, Lang used sound, specifically a whistle of "In the Hall of the Mountain King", to signify the presence of a murderer we didn't even need to see to fear. In Mabuse, Lang uses sound to hide criminal activity we can see. The opening scene, which features the above mentioned police informant in a counterfeiting factory, is covered with the sound of machines running. As such, the action on screen is acted silently, both adding suspense and commenting on how simultaneously useful and useless this new technology really was. Similarly, a key moment in the film, the murder of a doctor who is about to reveal the true identity of the criminal mastermind, the henchmen sent to kill him use the sound of car horns to cover the sound of a gun. Sound here masks the evil in a reversal of Lang's tactics in M. But Lang saves his most potent commentary for the revelation of Mabuse. In fact, he plays with the techniques he developed in M to play tricks on the audience. In M, we know there is a murderer there without seeing him because of his whistle. There is no killer in Mabuse, only the whistle. The revelation is still shocking today, and it sets up an "anything goes" dynamic for the rest of the film.
Being an international film from the 30s does wonders for helping the tension of the ending. It is an international film, so the good doctor may yet get away, but it was made during a time we associate with moral uprightness, so the good guys might prevail. Were this made in Hollywood, we would have no doubt that the doctor would be vanquished and order restored to the world. If it were made today, the doctor would lord over the ending like Noah Cross. Its setting is perfect for its unpredictability, though the film hardly needs you to know its setting to be thrilling. Mabuse is the perfect sort of genre film: technically perfect, ambitious, and willing to play off of the viewers' expectations to make things more thrilling.