The residents of Downton Abbey are fully immersed in the horrors of World War I as they prepare for a concert to help the village hospital prepare for war casualties.
When Matthew returns on leave from fighting in the trenches and introduces his new fiancee Lavinia to the family, Mary does her best to hide her feelings and wish them well.
Robert is offered a position as Colonel of the local volunteers and is disappointed to learn that it is only an honorary post and that he will not be going to the front. Sybil however is determined to do her bit and despite some of her family’s doubts, decides to train as a nurse, but she is shocked when chauffeur Branson reveals his feelings for her.
Below stairs Bates and Anna are becoming closer than ever, but he is distraught when his estranged wife Vera walks back into his life and vows to blackmail the family over Mary’s terrible scandal unless he gives their marriage another chance. Faced with an impossible choice, Bates breaks Anna’s heart and leaves Downton with Vera.
Meanwhile, Thomas deliberately injures himself to get sent home from the war and new housemaid Ethel makes an inauspicious start when she upsets the rest of the staff with her cocky, ambitious nature.