On a windy spring day in the Chilterns, the calm, organized life of science writer Joe Rose is shattered when he witnesses a tragic accident: a hot-air balloon with a boy trapped in its basket is being tossed by the wind, and in the attempt to save the child, a man is killed. A stranger named Jed Parry joins Rose in helping to bring the balloon to safety.

But unknown to Rose, something passes between Parry and himself on that day--something that gives birth to an obsession in Parry so powerful that it will test the limits of Rose's beloved rationalism, threaten the love of his wife, Clarissa, and drive him to the brink of murder and madness. Brilliant and compassionate, this is a novel of love, faith, and suspense, and of how life can change in an instant.