Ranking among the greatest of films ever made, Lang uses M as a means to explore the very state in which he resided for the majority of his early film-making career. Amidst swirling and mysterious shadows, the reflective nature of a glass pane and the oneiric, ethereal, brooding atmosphere lies something of the utmost importance: the implicit nature of humanity and moral ambiguity.

Unintentionally drawing on a similar real life serial killer in Peter Kurten, M describes the furore surrounding a child murderer, played with boggly-eyed precision by Peter Lorre. His shrill whistling of In the Hall of the Mountain King indicates his early ominous presence; truly a character that gives credence to convincing your children to stay away from strangers regardless of their whispers and promises. With another little girl murdered thus begins the rather wild and chaotic chase between the police and the criminal underworld to capture this killer and bring him to justice, a justice that is entirely unique to each organisation.

Such an ending is hard to describe, neither is commonly found due to the intensity and genuinely personal moral dilemma from which we are forced to endure. Frankly, it is rather easy to commit to brandishing that flaming stick at a murderer when he is but an objective killing machine, but when he begins to weep and display heartfelt dismay at his need to kill, then ambiguity seeps into proceedings. This is an ending crafted by the finest tinkerer of film, someone who understands the psychological elements that comprise a human being and the way in which people judge and are judged.

As per the state in which Lang was living at the time, he draws on those curious German expressionistic aspects of the period, using startling angles and sinister imagery to denote the intrinsic link between expressionism and identity. Whilst the dangerously comical elements of this movement aren’t obvious such as in earlier Weimar films, such as Das Kabinett des Doktor Caligari where the entire film is one giant spectacle, this is a much more subtle approach to the form – or as subtle as one can be when regarding and using expressionism. Reflective surfaces and shadows in the dark crevices of alleys are vital to the understanding of the film. In one scene, Lorre’s murderer looks into a mirror at a young girl and we, the audience, see the psychological strain and battle in his mind as he tries to free himself from the clutches of desperation and depravity; later, he describes how killing for him is almost a natural act, one that he attempts to fight each day, but to no avail.

There’s no doubt that Fritz Lang is among the most important and influential directors in the history of film. You can see little nuggets of M in later films of the film-noir period and particularly one certain film, Citizen Kane. He creates this world that merges the gap between fiction and reality; on one hand we have the fantastical and expressive elements of the period, yet we also have the gritty insight into certain societal ills.