Once a fortnight, Fred Crawford drives his battered truck on the toughest mail run in the world - across sand dunes, salt pans and the fearsome Stony Desert. For the men and women of the remote cattle stations on the way, Fred's visit is a welcome diversion, especially when he brings a new nursing sister for the tiny mission hospital at Birdsville. But trouble also arrives. Two vicious men have stowed away, fleeing a brutal murder.