Man With Four Lives

Novel with rather a weird premise: during World War I, while serving in France with the Canadian Army (as did the author), the protagonist of this tale has occasion to apparently kill the same German officer twice, and then to encounter him yet a third time, and witness his execution as a spy -- all of which has the cumulative effect of driving him stark raving mad. He eventually recovers, but I know you've only counted to three, and sure enough, years later when he and his wife are skiing in Switzerland he is rescued after an accident on the slopes by a young German who appears to be the same guy! The jacket blurb says the story "has as its core mystery and compelling suspense, though it is completely out of the category of detective fiction. It is a story of horror, though unlike The Werewolf of Paris or The Cadaver of Gideon Wyck, it has no time for atmosphere as it is preeminently a narrative of action. It takes as its background the World War, although it is not a war story." The New York Times reviewer called it "a quite exceptional achievement, [a] singular and powerful story."