The Serpent's Tooth — Michelle Paver

Belle must confront the man who brought her so much misery in her childhood and who now threatens her only chance of happiness.

Since she was twelve years old, Belle has lived with a secret -- a secret that cuts her off from her family and isolates her wherever she goes. Against the unfolding horror of the Great War, her search for peace takes her from the brittle gaiety of English country house society to the remote Scottish mansions where her grandmother's tragedy was played out, and to the battlefields of Flanders.

As the scarred and shattered men return from the trenches, and an influenza epidemic scythes across the country, Belle must finally discover a way to break free of her secret -- or lose her last chance of happiness.