A small-town English teacher, Jake Epping, learns from a friend that there is a portal that leads from the present back to 1960. Jake's friend asks him to help him stop John F. Kennedy's assassination by going back in time and finding out who really killed Kennedy... and killing them.

The past pulls out every weapon it has to keep Jake from reaching Dealey Plaza in time to save Kennedy. If he fails, it could mean death for Jake or others close to him - and if he succeeds, it could create a world in which he loses everything he's ever known. What is the cost of doing the right thing?