From amazon.com:

On November 22, 1963, three shots rang out in Dallas, President Kennedy died, and the world changed. What if you could change it back?

In this brilliantly conceived tour de force, Stephen King - who has absorbed the social, political, and popular culture of his generation more imaginatively and thoroughly than any other writer - takes listeners on an incredible journey into the past and the possibility of altering it.

It begins with Jake Epping, a 35-year-old English teacher in Lisbon Falls, Maine, who makes extra money teaching GED classes. He asks his students to write about an event that changed their lives, and one essay blows him away: a gruesome, harrowing story about the night more than 50 years ago when Harry Dunning’s father came home and killed his mother, his sister, and his brother with a sledgehammer. Reading the essay is a watershed moment for Jake, his life - like Harry’s, like America’s in 1963 - turning on a dime.

Not much later his friend Al, who owns the local diner, divulges a secret: his storeroom is a portal to the past, a particular day in 1958. And Al enlists Jake to take over the mission that has become his obsession - to prevent the Kennedy assassination.

So begins Jake’s new life as George Amberson, in a different world - of Ike and JFK and Elvis, of big American cars and sock hops and cigarette smoke everywhere. From the dank little city of Derry, Maine (where there’s Dunning business to conduct), to the warmhearted small town of Jodie, Texas, where Jake falls dangerously in love, every turn is leading, eventually of course, to a troubled loner named Lee Harvey Oswald and to Dallas, where the past becomes heart-stoppingly suspenseful - and where history might not be history anymore. Time-travel has never been so believable. Or so terrifying.