A whole German city holds its breath when in the early 30s there's a children murderer around. While of course the mothers are concerned about the safety of their children, the police and the politicians are worried about their status. And even for the crime scene itself the murderer becomes the main target, because the case leads to a strongly increasing number of policemen.
Today Fritz Lang's masterpiece "M" is watched as a revolutionary work that showed how much Lang was aware of the new possibilities that came with the sound revolution. An important scene for example is the cross-fading of the two conferences, the one in the kind of crime scene office and the one in the police office. There you see that both sides are actually talking quite the same and you hear sentences that are started in the crime scene office being ended in the police office. Now you might say that this isnt something special and that it is quite a clichee. But this movie invented it. And it works perfectly.
The real clou is that you don't HAVE to watch the movie, because it's oh so incredible important. You WANT to watch the movie and by the way it is incredible important. But it never feels like that, it feels like if it was produced maybe in the 60s or so and the way Lang increases the tension from scene to scene is just as genius as Peter Lorre in his carreer-defining performance as the children murderer (that's not a spoiler, it is actually shown in Lorres very first scene in this movie).
This is a 1930s black and white thriller, produced in Germany. So there is no Tarantino-esque overflow of blood and Hitchcocks suspense revolution hasn't even started yet. But instead of the boring movie you would expect due to this reasons, you see probably one of the best and especially one of the finest aged movies of all time.