Written by King in college in the 1960s, The Long Walk imagines young men competing in a deadly marathon for entertainment. A new film version is a reminder of how it anticipated our reality TV age.

One hundred teenage boys, selected by lottery from across the US, embark on a marathon with no finish line. Followed by armed soldiers in jeeps and watched by viewers all around the world, they must maintain a pace of 4mph (6.5km/h), and if they drop below the designated speed, they receive a warning. Three warnings and they are killed. The last boy walking gets to choose his own prize.

This is the grimly compelling concept of The Long Walk, a remarkably prescient novel that Stephen King wrote between 1966 and 1967, in his freshman year at college. Set in an alternate-history US that cowers under military rule, it was the first book that King penned, but was not published until 1979 – five years after Carrie had splashed onto bestseller lists like a bucket of blood dropped from the rafters. Now, 46 years on, as King turns 78, The Long Walk has finally been adapted into a film, released this weekend.

"I read The Long Walk right around the time I was doing I Am Legend [2007] and I fell in love with it," explains its director, Francis Lawrence, who is no stranger to deadly dystopian contests, having directed the last four Hunger Games films. "It became probably my favourite King book, and one of my favourite books [period]."

Lawrence points out how important it was to stay true to the spirit of a novel that is often labelled as King's most pessimistic, with its grim violence and chilling despair perhaps explaining why its journey to the screen has been so (aptly) arduous. First George A Romero and then Frank Darabont owned the rights to the book but failed to get it over the finish line, despite having previous with King in the form of Creepshow and The Dark Half, in Romero's case, and The Shawshank Redemption, The Green Mile and The Mist, in Darabont's. Lawrence succeeded where they failed, and did so without sanitising the harrowing story to make it more palatable for mainstream audiences. "You need to feel the miles and the time [passing], and feel the degradation – emotionally, psychologically, physically," he insists. "I wasn't going to dilute that and make the studio feel super-comfy with it."

"There's something relentlessly pessimistic about the nature of the story – lots of young people being killed," agrees freelance film programmer and writer Michael Blyth, who was a senior programmer at the British Film Institute when it mounted a month-long retrospective of King's films back in 2015. "But at the same time, there's a lot of kindness in there. The boys don't turn on each other. They're quite supportive. There's something about friendship and brotherhood that's very present in the book."

Simon Brown concurs. An independent scholar and member of the horror studies research group at Northumbria University who has taught on King, he is the author of Screening Stephen King: Adaptation and the Horror Genre in Film and Television. "The Long Walk is so bleak and miserable," he chuckles. "The only other King book that approaches this level of bleakness is Pet Sematary, which is a dialogue on death. But King is not a pessimist. He believes in the power of common decency, and most of his books end with whatever the monster is being defeated. The Long Walk is evidently a template for what would become a Stephen King book: you take a bunch of characters, put them into a situation, and see what they do. You can see that in The Stand, Under the Dome, The Mist… His books aren't about the........

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