Fritz Lang's story of the hunt for a sadistic child killer is both less graphic and more creepy than many horror films made today. In 1931, filmmakers were still figuring out what film could do and in this, Lang's first "talkie," Lang uses sound to great effect. While only about two-thirds of the film has sound, that absence makes the other one-third otherworldly as we move abruptly from sound to silence. The identity of the murderer is never really in doubt - M is all about the fear engendered by a seemingly-ordinary fellow who has some sort of evil inside him that compels him to kill the most innocent among us. Stand-up citizens become hyper-alert, forming an impromptu mob when an elderly man is seen talking with a young girl on the street. The exhausted police force is willing to strong-arm citizens (both stand-up and otherwise) to uncover the monster preying on Berlin's children. The criminal underworld is outraged that they are being lumped in with an inhuman killing machine. Only the killer goes about his day, cheerfully whistling "In the Hall of the Mountain King" from Grieg's Peer Gynt. (By the way, the "stunt whistling" is done by Lang himself and this marked the first time a musical theme was used to identify a particular character - a trick used by opera for years.) M also asks two questions that have been around at least since Euripides' Medea - are those who kill children evil, or merely sick? And, in any event, what's to be done with them?
M is genuinely astonishing. Small details carry so much visual weight - the empty place set at the kitchen table, the detritus of the criminals' hasty scurrying-away from the office building in which the murderer has sought shelter, the dark shadows that hide the criminals' kangaroo court, The similarities between the police and the criminal underground as made obvious, both in common camera set-ups used by both and by shared character traits. (And smoking. Lots and lots of smoking.) Oh, and there actually was a sort of Beggars' Guild in Berlin at the time.
Part of what makes M such a standout film is the fact that it doesn't let us off the hook. Parents know there's a murderer on the loose, yet many children still wander around alone. Then parents are willing to rip an innocent man limb from limb without any sort of police presence. At its heart, M's lesson is that we're all responsible for each other - a lesson the Nazis rising to power in the waning days of the Weimar Republic, roundly ignored.