A good walk spoiled. That’s the alarming mission for two Lance Corporals, tasked with getting a message across no-man’s land in Sam Mendes’ thrillingly shot 1917. Famously filmed in a handful of serpentine, segued takes, 1917 sees the young lads crossing a war-torn landscape, eerily empty following the apparent retreat of the German forces.

Schofield, a decorated foot soldier and Blake, a plucky, reliable comrade must take a message to a British unit several miles across dangerous country. The High Command believe the force is about to fall into a trap set by a much stronger enemy with the loss of over a thousand lives, including Blake’s brother.

1917 is a deliberately immersive experience. It’s also an unsettling – even a poetic - one that weaves a suspenseful spell. Leading us from trenches to dugouts, from craters to open countryside, from farmhouses to flame-wrecked towns, we experience everything the boys do, shot almost in real-time.

An atmosphere of surreal emptiness haunts the films, with hidden threats and dangers. Inflected with sci-fi and horror-film tones, it recalls A Quiet Place more than All Quiet on the Western Front. Unfettering us from the familiar visuals of a war-ravaged wasteland and dug-in immovability, it’s a film entirely about movement and revelation. We see only what the lads see.

Credit then to George MacKay (Schofield), angular-faced and as ashen as the visages in Peter Jackson’s They Shall Not Grow Old. In a bravura physical performance, how he stands, even how he holds his gun, tells you all you need to know about his experience, his character and his motivation. And when a double-mission arrives midstream, we’re as galvanized by his resurging spirit as he is.

In a film of rhythmical contrasts – wide field and high-sided dug out, blue sky and dust-dark tunnels, bone-dry tracks and river-chilled torrents – we’re lulled and gripped, carried and propelled. You can almost forget you’re watching two men walking. It’s a mercurial achievement.

Digging miles of trench in Salisbury Plain, Mendes has the stupendously talented cinematographer Roger Deakins follow the men in a series of uninterrupted takes which make you boggle afterwards at the logistics of it all. Standout sequences abound, particularly a night-time firestorm raging over a town, Schofield framed in hypnotized disorientation.

Punctuating it are cameos from some of Britain’s currently-cool thesps, a fabulously effective Andrew Scott as an inebriated officer and Benedict Cumberbatch as a more broom-up-the-backside one. But it does startle – ‘oh that’s Moriarty from Sherlock’, ‘there’s Sherlock himself’. It nearly breaks the spell.

The score, from Skyfall's Thomas Newman, is Oscar-nominated yet patchy. Anachronistic synths, Bond-sounding bombast, thrumming Kasbah rhythms, and plinky pianos, there’s a sound for each danger and dread. An operatic overture - Vaughan Williams on acid – is nicely hallucinatory though.

Richly crafted and simply scripted (largely by Mendes), it’s an easy film to follow. Brilliantly carried by George MacKay, endlessly varied, and keenly elemental, it’s a fabulous experience that takes you, like the boys, to places you’ve never seen.

Director Sam Mendes has kicked off the new decade with a landmark piece of cinema. 1917 has already been well-received at the Golden Globes, snagging Best Picture and Best Director, and more garlands seem certain to follow as the awards season wears on. George MacKay and Dean-Charles Chapman play Schofield and Blake, two unassuming corporals tasked with a near-impossible mission. The Germans have retreated, and the British vanguard, miles ahead of where our two protagonists are stationed, are looking to strike the final blow. But the German withdrawal has been skilfully stage-managed: the British front line is heading into a trap. It is up to Blake and Schofield to deliver a message to the commanding officer at the front and stop the dawn attack, saving 1600 lives in the process. If that weren’t incentive enough, amongst those set to go over the top (and thus to almost certain death) is Blake’s older brother, played by The Bodyguard’s Richard Madden.

Obvious comparisons can be drawn to Saving Private Ryan, and there are shades of Dunkirk here too – like Nolan’s picture, 1917 is an immaculate war epic, with a particular focus on time, recreating for the audience in vivid detail what it felt like to be part of the conflict. But whereas Dunkirk featured multiple plotlines, which advance and interweave hour by hour, Mendes has taken on a different and more difficult challenge. 1917’s storyline unfolds minute by minute, second by second, as if in real time, and the two-hour film appears as one continuous shot. This is, of course, is not quite the case: the film consists of a series of long takes, the balletic camerawork carefully choreographed by veteran cinematographer Roger Deakin (the behind-the-scenes footage is well worth a watch), and seamlessly stitched together using digital sorcery.

The illusion is nonetheless extraordinarily effective, making for a staggeringly immersive cinematic experience. We follow the two young corporals as they hurry down busy trenches, and slither through craters strewn with the corpses of men and horses. The cameras and set design really capture the eeriness of no-man’s-land and the haunting silence of the empty German trenches, which aren’t as abandoned as Blake and Schofield had hoped. There are some stunning sequences elsewhere, too: a dreamlike scene in a bombed-out village lit by flickering flares quickly turns into an infernal nightmare, a burning building illuminating foes hidden in the shadowy ruins. Here, and during a breathtaking later sequence on the battlefield itself, Thomas Newman’s grand score is an apt accompaniment to the action onscreen.

But beneath the technical mastery on display, there is peculiarly little to invest in. A trenchload of British actors have been shipped in for the production, but most are allotted unremarkable supporting roles. Colin Firth and Benedict Cumberbatch are resigned to stiff upper lip duty, while Daniel Mays is a gruff mid-ranking officer. The more empathetic Mark Strong is granted a fraction more screen time, and Andrew Scott glitters in his brief scene as a cynical captain who brims with gallows humour. Of the main protagonists, Chapman’s character Blake is of interest, transformed from a cheery lad who longs for his turkey dinners into a portrait of determination and gritted teeth, but MacKay’s Schofield is strangely opaque, his backstory tentatively set up and then left unexplored. One can only hope MacKay gets more chance to test his range as the lead in the upcoming True History of the Kelly Gang.

Another perplexing aspect of the film is the brightness and the colour palette, a mish-mash of ochres and bucolic pasture greens. It’s a different vision to the one traditionally associated with World War I, the gloomy, murky world of mud and wreckage captured in sepia photographs. The intention was perhaps to highlight the utter absurdity of the mission – the lunacy of two soldiers traversing such dangerous territory in broad daylight – but nevertheless the brightness is jarring and weirdly artificial. Nor does the film break new ground thematically – the race against time plot line is one of courage against adversity, while at points there is a critique of the First World War military hierarchy, the sense of lions led by donkeys. These are familiar, and not unevocative ideas, but they hardly take the war film into revolutionary territory. 1917 is clearly a deeply personal endeavour for Mendes: the end credits carry a dedication to the director’s grandfather, Alfred H. Mendes of the 1^st Rifles, “who told us the stories”. It’s a slight disappointment that this sentiment doesn’t wholly translate to the finished picture. Mendes’ picture is visually jaw-dropping, but somehow its emotional complexity fails to match its technical brilliance.