11.22.63, By Stephen King

Stephen King's new epic is arguably literature's first romantic-time-travelling-conspiracy-thriller.

Fusing The Time Traveler's Wife with an episode of Quantum Leap, King has produced The Time Traveler's Divorcee Goes Back to the Future to Prevent the Kennedy Assassination.

The divorcee in question is Jake Epping, devoted school teacher, newly directionless singleton and typical King hero. Observant and decent, he is haunted by the memory of his alcoholic ex-wife, Christy. Epping's failure to cure her addiction and save their marriage explains his otherwise barmy decision to change the course of history.

Like many King narrators, Epping's most important character trait is his credibility – vital if we are to believe the reality-bending quest he undertakes. Occasionally this means that Epping narrates to a point of exhausted irritation. His eye for Kingly ephemera (cars, pop music, obscure short stories) and his tendency to over-share his adventures in teaching inspire the occasional skim or guiltily premature page-turn. For the most part, however, Epping convinces. He's as average a Joe as you or I – it's just that he's discovered a tear in the fabric of the space-time continuum.

Wisely, King doesn't dwell on the sci-fi mechanics of his high-concept MacGuffin: I for one was grateful there were no Terminator-like games where Epping watches his younger self play baseball. Like Bill Murray in Groundhog Day, Epping's surreal trial by time zone begins with little explanation, and in the most mundane surroundings. It is typical of 11.22.63's hymn to folksy, small-town America that the temporal wormhole is located in Al's local diner.

Al himself has been visiting the past on a regular basis, placing bets, purchasing cheap meat and waxing lyrical about more innocent times. King and Epping know better: courtesy, tasty food and a sense of community contend with ignorance, racial prejudice and sexual discrimination.

Al is one of many enjoyable, if slightly clunky plot devices: ditto the prefatory murder story set in 1958. Al sets up the rules Epping must follow. The most ingenious of these is that while history can be changed, it resists such attempts with all its might. Epping encounters flat tires, tumbles down stairs and, ultimately, far worse on his way to achieving his goal. This more than justifies King's time-travelling conceit. 11.22.63 is unusually sensitive to cause and effect; to the knowledge that one good turn doesn't necessarily lead to another.

Epping rewinds to Maine in autumn 1958 – hence the choice of saving JFK. (I myself would have stopped Herman's Hermits.) This starting point means that 11.22.63 follows the same trajectory as James Ellroy's seminal novel about the Kennedy assassination, American Tabloid. Both authors have great fun transforming the unstable facts of the assassination plots into games of narrative join-the-dots. But whereas Ellroy creates a crazy matrix of law, politics, sex, big business and underworld shenanigans, King slows the pace and focuses on the sort of small town in Maine in which he was raised.

Epping teaches at the local school, falls in love with a librarian (Sadie Clayton) and becomes a fixture in the local community. History, he slowly realises, is personal as well as public. People may remember exactly where they were when they heard of Kennedy's assassination but King knows that we recall just as vividly falling in love, learning a friend has died, or the day we made a difference to another person's life.

11.22.63 is quite something, an exciting, intelligent if overlong book that underlines all King's powers as a novelist while exposing some of his flaws. Twenty-first-century King is a strange beast: populist and high-minded, artless and self-conscious; as ambitious as any novelist but always anxious about that ambition. Take Epping, who can sound spookily similar to the King of the excellent "memoir of the craft", On Writing. One moment he alludes to Paul Bowles and Percy Shelley. Then, lest you mistake him for one of them thar "fancy schmancy" literary snobs, he delivers forceful home-spun critiques of his students' prose: "they wrote like little old men and little old ladies, pursey-mouthed and ooo, don't slip on the icy patch, Mildred."

The more I read of 11.22.63, the more I was reminded of King's possible masterpiece, the short story "Rita Hayworth and Shawshank Redemption". (11.22.63 even name-checks the prison.) Both feature good but damaged men imprisoned by time as well as place. Both narrators are assisted by older, wiser guides, both use literature to help protégées and both are haunted by memories of alcohol-induced marital breakdown. In the end, both are redeemed by coming to terms with the past, learning to make better choices and escaping to a brighter future.

Whether the 740 pages of 11.22.63 will outlast the 94 of "The Shawshank Redemption" is not for me to say. History will be the judge of that. But then, we knew that already.

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