Jake Epping, an ordinary high school teacher, is presented with a chance to change history. When a longtime friend shows Jake how to travel back in time, he tasks Jake with a mission he has been trying in vain to complete: stopping the assassination of John F. Kennedy on Nov. 22, 1963. Jake quickly learns that the past does not want to be changed, and that his attempts to divert the course of history can quickly turn dangerous.
Jake Epping is burned out and lost. His ex-wife has moved on, his students are always distracted, and his novel went nowhere. Then one of his dearest friends, Al Templeton, shows him the rabbit hole, a secret time portal that leads back to 1960. Al asks Jake to head back to the past and create a better world by stopping the Kennedy assassination. Jake heads down the rabbit hole to begin his mission but finds that changing the past is far more dangerous than he ever would have dreamed.
Thrown by the enormity of his goal, Jake decides the one thing he can do to make a real difference is save the family of his friend Harry Dunning. Harry's family was murdered in a small Kentucky town by Harry's out-of-control father, Frank. But does Jake have what it takes to kill a man and what are the consequences of violence, even against some as dangerous as Frank?
Jake finds an unlikely ally in local drifter Bill Turcote. The pair travel to Dallas, where Jake begins living a double life, and both of them trail Lee Harvey Oswald. Trailing Oswald takes Jake into the dark side of Dallas, where Jake realizes Oswald may not be the only threat Kennedy will have to face.
Jake and Bill's partnership starts to struggle as they discover more secrets surrounding the unpredictable Lee Harvey Oswald. The conspiracy involving Oswald deepens, while romance blooms for Jake and Sadie. But by becoming involved with an innocent bystander, has Jake placed his new love in danger?
Everything begins to fall apart as Jake struggles to live two lives: teacher and time traveler. When Sadie's life is threatened, Jake has to make a terrible choice, leaving Bill to his own devices. Lee Harvey Oswald takes steps that will lead him into a date with destiny.
It's October 1963, and the gathering storm of threats in Dallas continues to build. Jake must take drastic action to establish the full dimensions of the threat to Kennedy. And amidst it all, he's hit with an unexpected death and a bitter betrayal from one of those closest to him.
The end is near, and Jake is not up to the task. Sadie scrambles to pick up the pieces, but no one knows the mission as well as Jake. Kennedy and the assassin are on a collision path - but has Jake changed things enough in the past to alter the course of events? The days are counting down as 11.22.63 draws near.