On the first day of the Somme enlisted railwayman Jim Stringer lies trapped in a shell hole, smoking cigarette after cigarette under the bullets and the blazing sun. He calculates his chances of survival - even before they departed for France, a member of Jim's unit had been found dead. During the stand-off that follows, Jim and his comrades must operate by night the vitally important trains carrying munitions to the Front, through a ghostly landscape of shattered trees where high explosive and shrapnel shells rain down. Close co-operation and trust are vital. Yet proof piles up of an enemy within, and as a ferocious military policeman pursues his investigation into the original killing, the finger of accusation begins to point towards Jim himself . . .