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