Harry (Daniel Auteuil) is a successful sales consultant for a large bank, but his marriage is over. After he forgets to pick up his little daughters at the railway station, his wife (Miou-Miou) quite understandably bars him from further contact. Angry, depressed, and driving alone on a wet night, he literally "runs into" Georges (Pascal Duquenne), an adult with trisomy-21.

Georges has escaped the institution where he was placed by his sister at the death of his beloved mother four years ago. Reduced to ineffectiveness and irrational behavior, Harry is simply unable to rid himself of Georges, allows him to take over his life, and accepts him as a friend on equal terms.

Georges draws Harry into an escapade with his fellow inmates that ends in a late-night frolic at a beach carnival and a spectacular display of fireworks for Harry's children that lures the family back. Georges is in love with Nathalie, a fellow inmate also with trisomy-21, and they share wonderful, neatly ironic daydreams of leading roles in a Mongol horde.

But Georges knows that they can never find happiness together. He eats a box of chocolates, to which he is greatly allergic, and calmly steps off the roof of Harry's skyscraper bank. Thanks to Georges, Harry's life is not only restored, it is vastly improved.