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].”