Greatly admired for the rigor and originality of its construction, Fritz Lang's masterpiece is a terrifying excursion into an urban underworld where it is difficult to distinguish morally between the activities of organized crime and organized law enforcement. Peter Lorre gives his immortal performance as a pathetic child murderer pursued by both the law and the syndicate. In its themes, style, and mood, all of which express a kind of entrapment that is at once psychological and based in reality, M is a precursor not only to Lang's American films but to American film noir in general. In a highly expressive early soundtrack, music is limited to the Peer Gynt theme, which both torments the murderer and hauntingly announces his presence in place of the image. Off-screen dialogue accompanied by shadow images; sound overlapping scenes, binding one to the next; silences broken by the ticking of a clock, a police whistle, or a mother's desperate shriek are ways in which sound and image are ingeniously fused to enhance the plot.