Time and Time Again by Ben Elton
It's the 1st of June 1914 and Hugh Stanton, ex-soldier and celebrated adventurer is quite literally the loneliest man on earth. No one he has ever known or loved has been born yet. Perhaps now they never will be. Stanton knows that a great and terrible war is coming. A collective suicidal madness that will destroy European civilization and bring misery to millions in the century to come. He knows this because, for him, that century is already history. Somehow he must change that history. He must prevent the war. A war that will begin with a single bullet. But can a single bullet truly corrupt an entire century? And, if so, could another single bullet save it?