Munich – The Edge of War is a highly engrossing two hours that spins a tense fictional yarn while remaining faithful to the broader historical record. In its counterfactual version of the 1938 Munich Agreement, Christian Schwochow’s film is driven not by the relationship between Neville Chamberlain (Jeremy Irons) and Adolf Hitler (Ulrich Matthes), but the fictional Hugh Legat (George McKay) and Paul von Hartmann (Jannis Niewohner), a British civil servant and German diplomat, respectively.

Although Legat and Hartmann are on opposite sides of the nascent war, the young men are good friends from their time at Oxford University, or they were until Hartmann was seduced by Hitler’s nationalism in 1933, with which Legat disagreed. However, by 1938, after years in his government job, Hartmann sees the Nazis for what they really are and he resolves to stop them at the Munich conference by sharing a damning memo with his old friend Hugh Legat.

What are the chances of these university chums becoming diplomatic counterparts? Slim to none, of course. But Ben Power’s script, which is adapted from Robert Harris’s novel, manages to lend heart and credibility to these characters, which are skilfully realised by McKay and Niewohner.

McKay, who has a knack for script choice as well as acting, performs Legat with a diligent anxiety as he rushes through the halls of power, acutely aware that war is all but inevitable. Hartmann is more assured in his working life, yet he has a righteous anger that risks imprisonment, torture and death not just for himself but also Helen (Sandra Huller), his lover and confidante.

McKay and Niewohner may be the fictional heart of this story, but the best work comes from Jeremy Irons, who gives a charming and complex performance as Prime Minister Neville Chamberlain, a figure blighted by a terrible dramatic irony.

Chamberlain’s diction is brusque and cut glass, yet he is shown to be kindly and empathetic toward those far down the chain of command. Captured also is the prime minister’s heartfelt desire to avoid war, especially during a garden scene in which he laments that he was too old to fight in the Great War and effect any kind of change. Now, as prime minister, Chamberlain declares that he will do everything in his power to prevent another catastrophic waste of human life. Irons’ magnetism may be strongest during an impromptu meeting late in the film that is utterly fictitious yet engrossing and dangerous, such is Robert Harris’s deft skill for developing authentic counterfactual histories.

Our disbelief is suspended even when Adolf Hitler (Ulrich Matthes) appears in several intimate scenes with Hartmann. Matthes, who played Joseph Goebbels in Downfall, does not have Hitler’s likeness, he is too gaunt and angular, yet his voice has a similar resonance to Hitler’s speaking voice, which was recorded surreptitiously on 4 June 1942.

All the merits of performance and narrative are complimented by aesthetics and period detail. The airy locations are lit and photographed to suit the mood, which is particularly effective during Legat’s severe backroom meetings on espionage and duty. There’s a strong, punchy colour palette, too, with shades of blue being the dominant accent. These are the polished edges of a film that may be a minor entry in the vast library of WWII cinema but a robust counterfactual yarn, nonetheless.