Stephen and Isabelle start an illicit affair, with ends up having huge consequences for them both. Years later in 1916, Stephen finds himself serving on the Western Front in the very place where he experienced his great love. He meets Jack Firebrace, a tunneller who ends up helping him endure the ravages of war and enables him to make peace with his feelings for Isabelle, who he is set to meet again.

Stephen recovers from his injuries but he is still haunted by memories of his affair with Isabelle. Stephen ends up unexpectedly meeting Isabelle again as he and his men prepare for a major offensive at The Somme The battle is devastating and in the months that follow, Stephen starts to find some comfort in his friendship with Jack Firebrace. After Isabelle's sister Jeanne admits the secret which Isabelle had kept hidden from him, Stephen starts to believe that there really is a future worth fighting for.