There’s no looking away. The battlefield drama 1917 will play out in a surprising form—as if it were one continuous shot, tracking two British soldiers as they race through a carnage-strewn landscape to deliver a message that might save 1,600 lives.

George MacKay (of 11.22.63 and Captain Fantastic) and Dean-Charles Chapman (Tommen Baratheon on Game of Thrones) play Schofield and Blake, who are given orders to cross enemy territory to hand-deliver vital news that can be conveyed no other way. The film runs one hour and 50 minutes, and the story plays out in real time.

“It was fundamentally an emotional choice,” director Sam Mendes told Vanity Fair. “I wanted to travel every step with these men—to breathe every breath with them. It needed to be visceral and immersive. What they are asked to do is almost impossibly difficult. The way the movie is made is designed to bring you as close as possible to that experience.”

The American Beauty and Skyfall director cowrote the script with Krysty Wilson-Cairns (Penny Dreadful) and spent nine months preparing with veteran cinematographer Roger Deakins (an Oscar winner for 2017’s Blade Runner 2049) to make sure the shots and scenes were matched and timed seamlessly as they moved between locations while shooting this spring.

This behind-the-scenes video illustrates some of the challenges they faced, from making sure the late-day lighting remained consistent as the story unfolded to disguising the transitions between cuts. “What cuts?” Mendes answered coyly when asked about techniques for hiding them.

This type of approach has been attempted before, notably Hitchcock’s Rope in 1948, which played out entirely in one room. The 2011 horror-thriller Silent House and 2014’s Birdman pushed the technique further, one moving in and around a woodland home and the other circulating through Manhattan’s theater district.

What differentiates 1917 is its epic scale, journeying across a vast and chaotic outdoor landscape while remaining intimately focused on its two central characters. Along this odyssey they encounter other characters played by Benedict Cumberbatch, Claire Duburcq, Colin Firth, Richard Madden, Andrew Scott, and Mark Strong.

“The movie is essentially linear, and moves through a huge variety of different locations,” Mendes said. “From the trenches, to No Man’s Land, to open countryside, farmland, orchards, rivers, woods, and bombed-out towns. It bears witness to the staggering destruction wrought by the war, and yet it is a fundamentally human story about two young and inexperienced soldiers racing against the clock. So it adheres more to the form of a thriller than a conventional war movie.”