Even for King this is a very fat novel, running for many hundreds of pages. Jake Epping, a teacher abandoned by his alcoholic wife, is friendly with the proprietor of a neighborhood diner noted for its remarkably low prices. The proprietor reveals he is dying of cancer, but before he goes, lays on Epping the news that his low prices come from a time gate in his diner that sent him back to 1958, where he stocked up on cheap (by 2011 standards) items. His ultimate plan was to live in the past up to the time John Kennedy was assassinated, and avert this. The cancer assures he won't live long enough. Epping is provided with fake papers in a false name, which is never explained, as not only was he not born until 1972, but his parents were not even acquainted in 1958.

Epping uses a list of sports events to increase his nest egg of 1958 currency, and sets out to see if the past can really be changed by preventing a drunk from murdering his wife and three children, leaving a fourth child crippled and brain damaged. He has some success, as the wife is injured and one child is left dead, so he returns to 2011, and tries again. He succeeds, and heads for Texas, where he settles in a small town near Dallas. Using fake papers he gets works as a school teacher, and falls in love with the new school librarian, who ultimately tells him an appalling tale of abuse at the hands of her ex-husband. Epping begins to track Lee Harvey Oswald and his family, discovering his mother is bad enough to earn Oswald some sympathy.

Eppping holds off on snuffing Oswald on the chance he really was innocent, but is convinced, and rushes to the School Book Depository with his lady friend on the crucial date. Oswald is killed, as is Epping's lady. At this point I expected a resolution along the lines of David Gerrold's novel "The Man Who Folded Himself". But when Epping returns to 2011 after some hostile questioning by Dallas law enforcement, he finds Maine has joined Canada, an earthquake killing 7000 hit Los Angeles on November 24, 1963, and the world of 2011 is polluted, ruined and depressing. Kennedy was narrowly re-elected in 1964, but never got the civil rights legislation passed which in OTL Lyndon Johnson achieved. JFK was succeeded by George Wallace, who nuked Hanoi, and things went down hill from that. Scientists are predicting the planet will fragment in 2080, and saving JFK has threatened not Earth or the Solar System, or even the universe, but "all reality". Clearly I had forgotten King is noted for horror rather than scientific plausibility.