Perhaps ultimately, men think only of their own survival, or if that's barely an option in a bunker in late April 1945, the fastest way to die. There were two moments in Oliver Hirschbiegel's extraordinary film of Hitler's last hours that caught my breath. How often does today's cinema do that? They were, perhaps, moments well documented on the historical record but even then, they were barely believable as acts carried out by flesh and blood human beings. Sitting here in a few hours of hindsight, I still balk at the reality of the events. How could a father, or a mother, believe in a world vision so wholeheartedly, so wretchedly that they would be willing to kill their own children to 'protect' them from an uncertain future?

In Downfall, Bruno Ganz, giving a mesmerising performance as Austrian painter turned malevolent dictator, Adolf Hitler, underlines his theory of natural selection - that being the fittest, the strongest is the ultimate and only natural road to survival. 'No compassion,' was his war-cry. Surely one of the first rules of any society that wants to propagate its ideals and culture is 'don't murder the children'? In a scene as chilling as it could be, a mother administers, at first, a bitter sleeping draft and then a poison to her six children and watches them die, one after the other. And the audience is spared no detail. It is a direction coup of extraordinary power that the signifier of their death is the baring of their feet (the blanket to cover their faces being too short to cover both ends of the body). The children's father, standing outside, is an accomplice, a man who could not bear to do what he also believed was necessary. It's not that heartening to know that they too die soon afterwards at their own hands. It's all the more horrific, that sense of awful premeditation. Once they knew that Hitler would fall, their idealised future fell with him and so the Goebbels decided to exterminate their own children rather than face a future without Nazism at its core.

At least two people I have spoken to since seeing the movie said that they could not watch a film in which children are murdered by their parents. I understand their reluctance. This gross act of barbarism in the name of Nazi purity is probably the most heinous act I have ever seen on a cinema screen but if it really did happen, in the context of Downfall, the movie, then it must be shown. I don't know if what the real Frau Goebbels did after the six executions was true (she shuffled cards and played Solitaire in this version of horrific history - how much more 'solitaire' could she be?) but her hideous act was so contemptible, you just sat there disbelieving. You played with a hope that she might burn in a very special level of hell. And Hitler called her 'the bravest mother in Germany' in the movie.

Downfall charts the end of the 3rd Reich, the end of Hitler, Eva Braun and the most savage, monstrous regime of the 20th century. It doesn't flinch or blink at what must have been a powerfully difficult subject for any German film-maker to take on. All credit to producer/writer Bernd Eichinger and the director who face up to every fact and presents each with no fanfare nor unequivocal sympathy or prejudgement. Here are the monsters of history. How much humanity can we, the audience, impose upon them?

Over black before a single image, we hear an old woman's voice describing her time with Hitler. We don't know who she is yet. In a short introductory flashback, we are introduced to Traudl Junge (Alexandra Maria Lara), the young woman who will become Hitler's secretary. Hitler warms to her based on her looks (one assumes) and where she hails from. Her first attempt at typing for him results in gibberish. He is kind enough to give her a second chance. We then slam forward to the last hours in Berlin before the Russians' advance strangles the Nazis for good. Seen through Traudl's naïve point of view, Hitler is a sick man fighting for the good name and honour of Germany. She buys into all this, never questioning but in her defence; you are a normal twenty something in Europe. How could anyone suspect what a cadre of officers urged by Hitler was capable of? There was no precedent for this wickedness so therefore no basis on which to suspect. How can one be guilty of not thinking the unthinkable?

Traudl's true 'every woman' status clicks into place after she discovers what is to become of the Goebbels children. No explicit word is spoken, no words for this act of ultimate barbarism. Her reaction is perfect; profound, uncomprehending, physical shock. At that moment it's as if she had been placed next to Hitler after just being born. There is no understanding of such cruelty in her eyes. She is the filter through which we can watch this movie, the 'every woman' character who holds our morality and ordinariness up against the selection of inhuman monsters led by a non-smoking, teetotal vegetarian. One of the most monstrous was the man standing outside the door while his children were murdered by his wife: Joseph Goebbels.

'The Poisoned Dwarf' as the Allies knew him is cast as a pinched faced shark, a sleek pitch black haired predator with eyes darker than any great white. The actor, Ulrich Matthes, is a casting coup. He doesn't have to act. His mere presence is enough to suggest the unending levels of cruelty he propagated. He sheds a few tears too and coming from that face, you do not believe one salty drop. You also got the sense that if this man ever smiled, the whole film would fall. His wife, played by Corinna Harfouch, is colder than the deepest fish, steelier than any blade. Her eldest child can sense something is wrong and fights against the sleeping draft. It takes two adults to force feed it to her. It's horrific to see children die by their mother's hand but it's twice as horrific to see a child struggle against what she could barely comprehend. This is my mother. She is killing me.

The other moment that affected me was a simple cut. To what, I won't reveal but I will say that the fall of Nazism was accompanied by a huge number of suicides and I can only conclude that these men (for they were all men) knew exactly what they were a part of. Death by their own hand was a way of avoiding execution, global revulsion and being hunted for the rest of their lives. Hitler's architect and close friend, Albert Speer, is the only man within Hitler's inner circle who comes out of the movie with any shred of dignity or decency. Played stoically by Heino Ferch, he admits to his leader that he disobeyed orders of great cruelty and actively did the opposite. Here is a man who didn't have the strength (as no single man had) to question and halt the atrocities but on his own terms he did what he could from the Nazi inner circle. He later claims he knew very little and the Nuremberg International Military Tribunal showed him some clemency (the twenty years of imprisonment type of clemency) but Speer's reputation as a 'good Nazi' is still in debate over twenty four years after his death in London in 1981.

By late April 1945, Hitler was a shadow of his former, ebullient self. Ravaged by what's now believed to be Parkinson's Disease, he prowls the bunker, spine folded forward, one hand shaking behind his back. His downfall also brought on a sense of denial that may have been interpreted as stress-induced madness. He certainly wasn't listening to his generals, all of whom he accused of being traitors simply by dint of their losing ground to the Russians. One of his generals (whom Hitler sentences to death in a fit of pique) marches to the leader's side and demands to be told why. Hitler is impressed by the man's fortitude and bravery and hands him command of another doomed regiment. He deadpans that as a choice between the two he'd rather have been shot. This line of dialogue sums up the futility of the Nazi's position at this crucial moment in the Allies' push for Berlin.

Eva Braun (Juliane Köhler) is well known as Hitler's mistress and in the final hours, wife. But like Traudl, you get the impression that she knows nothing about what the Nazis were really capable of. She's a freewheeler but when the crunch comes she also stands by her man until the very end. Her determination to go down dancing is touching if a little inappropriate as the bombs blast in the windows. Her friendship with Traudl is sincere (like an older sister to an impressionable younger sibling) and to see the two of them 'nip out of the bunker' for a cigarette is amusing even if they do have to come straight back in again as the shelling starts. But despite the horror and the gloom, the director chooses to signal Hitler's own suicide with a visual gag. After the gunshot, several soldiers and generals all light up, something verboten in the bunker while Der Fürhrer was still alive.

Once the bunker's residents have either left or gone to hell, the Russians arrive. It's a testament to the film's gripping nature that the fate of the higher echelon of Nazi officers is not the core of the film. It is Traudl. Wearing a Nazi jacket trying to downplay her femininity (difficult as she has a beautiful face) she moves through the Russian ranks hoping to escape by virtue of her sex. How or if she manages and what help comes from a tragic sub-plot of the film I won't spoil.

In all, Downfall is an extraordinarily assured work. It sensitively treats a sensational subject with restraint and detachment. It manages to place a crucial moment in history at arm's length but close enough that we can smell the cordite and the grim stench of the bloody operating rooms. Any closer and it would have become exploitative. I can't imagine a better handling of the subject matter and let's hope it's gone some way to rid the German people of some uncomfortable baggage. After all, monsters grow in all climes, countries and circumstances…