Which of us would not travel back in time, if we could, to undo some of the horrors of the past? This is the perennially fascinating question that Stephen King has been pondering.

Jake Epping, the hero of King’s new book 11.22.63, is not a scientist but a divorced high school teacher from Maine. Jake is puzzled how his friend Al, who seemed hale and hearty when they last met – 22 hours ago – has suddenly lost 30lb and developed terminal cancer.

The answer lies in the pantry of Al’s diner, as does the mystery of how Al can serve the cheapest hamburgers in town and still turn a profit. A door in the pantry is, in fact, a portal to 1958. It turns out that Al has been buying prime minced steak at 1958 prices, paid for by his winnings bet on sporting events whose results he already knows, and bringing the meat back to the present. Revealing all to Epping, he persuades him to go back and rewrite history for the sake of America and the world. The title of the book is the day that President John F Kennedy was shot. The quest to stop Lee Harvey Oswald is at the heart of 11.22.63, a mission that, if successful, would extend the Age of Camelot and spawn a brighter America. Or would it?

King has written 40 bestsellers, and has virtually invented his own genre of “small-town-thriller-horror”: many of his works, such as Carrie (1974), about a schoolgirl with supernatural powers, and Christine (1983) – a possessed 1958 Plymouth Fury – explore the hidden darkness and terrors of suburban America.

King previously explored time travel in his 1990 novella The Langoliers, in which a group of airline passengers become stuck in a time warp and have to make their way to the present. 11.22.63 marks a definite maturing of literary command and ambition and is a step up from recent, more standard works, such as Cell (2006), about an electrical pulse that turns anyone using their mobile phone into a zombie.

The key to any novel set in an alternate reality is credible world-building, the steady accumulation of detail – preferably lightly distributed – that brings the story alive. King succeeds in this, partly by drawing on his own memories. He was 11 years old in 1958, when root beer tasted so rich and strong that it was almost intoxicating, when families gathered around their first television sets to watch Lassie, and black and Jewish people suffered discrimination that was all the more shocking for being so casual.

11.22.63 is especially intriguing on the subject of identity – notably Epping’s attempts to juggle his real identity with his assumed one: to live his new life convincingly, he must forget everything he knows about the future during his long sojourn in the past. He is not always successful, or indeed subtle: at one point he carelessly pulls a mobile phone from his pocket, several decades before the device was invented.

King has now reached that enviable stage in a writer’s career when he can write as much as he wants about whatever he likes without, it sometimes seems, an editor’s critical eye. The book weighs in at around 750 pages and is too long. The tension flags in the middle section while Epping is stalking Oswald during the early 1960s, even though King drops in several sub-plots and a love interest in an attempt to keep the narrative going.

Yet 11.22.63 also raises some unsettling questions about the consequences for the present of changing the past. Maybe the assassination of JFK was necessary, as, if it hadn’t happened, something far more terrible might have occurred. Time itself is the protagonist of 11.22.63, stubborn and rebellious, elastic and unforgiving and decidedly unwilling to be so easily reshaped by the whims of a temporary visitor from the future.

Adam LeBor is author of ‘The Budapest Protocol’ (Beautiful Books)

11.22.63, by Stephen King, Hodder & Stoughton, RRP£19.99, 752 pages

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