1915. On the eastern front, Michael is forced to make a terrible choice, while on the western front Tommy's regiment experiments with a dangerous new weapon. When Tommy is immersed in battle – only to receive unexpected help while collecting the wounded – while Michael and his comrades engage in hand-to-hand combat after being ambushed by Russian soldiers on the Eastern Front. Returning home on leave, he is overjoyed to marry Katie, but struggles to reconcile his old life with the terrible things he has seen and done. Meanwhile, Tommy sustains a serious injury and recovers in an army hospital, where he takes a shine to x-ray assistant Joanna

1917. Michael is taken prisoner, and Joanna has some big news for Tommy. The soldiers are haunted by memories of their dead friends. However, Michael soon has more to worry about when his trench is attacked by British soldiers and he and young comrade Freddie are taken prisoner. Meanwhile, Tommy sinks toward despair, convinced the war is never going to end, so he talks his way on to the prisoner detail as a way of sneaking off to see Joanna at the hospital – and in their stolen time together, she has big news to tell him