Joe Morrissey and his girlfriend Claire are about to open a bottle of champagne when a cry interrupts them. A hot-air balloon with a child in the basket and an adult being dragged behind is trying to crash-land in a field. Joe immediately joins in with an effort to bring the balloon to safety, but in the ensuing rescue attempt a man is killed.

Witness to this tragic accident is bystander, Jed Parry. Sharing this powerful event burns a devastating obsession into Jed's soul. Delusional and dangerous, Jed's fixation gradually uproots Joe's life, testing the limits of his beloved rationalism, threatening the love of Claire and driving him to the brink of murder and madness. Based on the novel by Ian McEwan.