Jack and Kate, who have been together since college, are at JFK Airport, where Jack is about to leave to take up a twelve-month internship with Barclays in London. Kate fears the separation will be detrimental to their relationship and asks him not to go, but he reassures her, saying their love is strong enough to last, and he flies out.
Thirteen years later, Jack is now a bachelor living a carefree life as a Wall Street executive in New York City. At work, he is putting together a multi-billion dollar merger and has ordered an emergency meeting on Christmas Day. In his office, on Christmas Eve, he gets a message to contact Kate, but, even though he remembers her, he dismisses it, apparently uninterested.
On his way home, he is in a convenience store when a young man, Cash, enters claiming to have a winning lottery ticket worth $238, but the store clerk refuses him, saying the ticket is a forgery. Cash pulls out a gun and threatens him, so Jack offers to buy the ticket and Cash eventually agrees. Outside, Jack tries to help Cash, to which he responds by asking Jack if anything is missing from his life. Jack says he has everything he needs, whereupon Cash enigmatically remarks that Jack has brought upon himself what is now going to happen, and walks away. A puzzled Jack returns to his penthouse and sleeps.
On Christmas Day, Jack wakes up in a suburban New Jersey bedroom with Kate and two children. He rushes out to his condo and office in New York, but both doormen refuse his entrance and do not recognize him. Jack runs out into the street and encounters Cash driving Jack’s Ferrari. Although Cash offers to explain what is happening, all he says is a vague reference to “The Organization” and that Jack is getting “a glimpse” that will help him to figure out for himself what it’s about.
Jack slowly realizes that he is living the kind of life he might have had if he had stayed in the United States with Kate as she had asked. He has a modest family life, where he is a car tire salesman for Kate’s father and Kate is a non-profit lawyer. Jack’s young daughter, Annie, thinks he is an alien but a friendly one and assists him in fitting into his new life. With a few setbacks, Jack begins to succeed, bonding with his children, falling in love with his wife and working hard at his job.
Taking advantage of a chance meeting when his former boss, chairman Peter Lassiter, comes in to have a tire blowout fixed, he impresses him with his business savvy and Lassiter invites him to his office, where Jack worked in his ‘other’ life. There, after a short interview, Lassiter offers him a position. While he is excited by the potential salary and other perks, Kate argues that they are very happy and they should be thankful for the life they have.
Having decided that he now likes this ‘other’ life, Jack again sees Cash, now a store clerk. He demands to stay in this life, but Cash tells him there is no choice: “a glimpse”, by definition, is an impermanent thing. That night, Jack tries to stay awake, but fails and wakes the “next day”, Christmas Day, to find himself in his original life. He forgoes closing the acquisition deal to intercept Kate, finding her moving out of a luxury townhouse before flying to Paris. Like Jack, she has focused on her career, and has become a very wealthy corporate lawyer. She had only called him to return a box of his old possessions. He chases after her to the airport and, in an effort to stop her leaving, describes in detail their children and family life he had seen. Intrigued, she eventually agrees to go with him for a coffee. From a distance, they are seen talking inaudibly over their coffees.