Two years into World War I, Matthew Crawley is an officer at the Battle of the Somme. At home, Lord Grantham has been made an officer of the local regiment and is eager to head off to the front himself.
Branson teaches Edith how to drive, William is anxious to enlist over the objections of his father and Sybil decides to train as a nurse.
Isobel is furious when she finds out that Countess Violet has led Dr. Clarkson to believe that both William and Molesley have medical conditions that would make them unsuitable for military service. She goes to Clarkson who appreciates that Violet only meant to spare both men the rigors of combat, but will make sure the records are updated. This is good news for William, but Molesley, not really wanting to face battle, is unconvincing when he privately tells Clarkson that the Dowager Countess was, in fact, correct in her information about his health.
With one less footman, Mr. Bates attending his mother's funeral and the need to break in the new maid, Ethel Parks, standards at Downton are hard to maintain, giving Carson much more work to do.
Mary returns on the train with Bates and learns that Matthew is engaged to Miss Lavinia Swire. Matthew and Lavinia appear for a benefit concert being given at Downton to raise funds for the war effort. Lord Grantham throws two women out who infiltrated the concert in order to hand white feathers, symbolizing cowardice, to any healthy-looking man not in uniform.
Bates tells Anna that his mother left him more money than he'd thought which means he can finally pressure his wife to give him a divorce.
Vera Bates has other plans. Thanks to a letter from O'Brien, she has left her maid's job to demand that he resign his position, return with her to London and remain her husband. If not, she will go to the papers with the scandalous story about Mary and Mr. Pamuk that will not only cause a scandal for the family, but also implicate Anna. Mrs. Hughes overhears the conversation through a grate in the adjoining room.
Grantham is furious when Bates resigns without explanation, chastizing him for his lack of loyalty after all of the faith he was shown. Mrs. Hughes tells Mr. Carson what she heard and Carson goes to Grantham, leaving out the details, but explaining that Bates left to prevent his wife from sullying the family honor.
Mary begins seeing Sir Richard Carlisle, the owner of a string of scandal sheets, to the disappointment of her father who is reeling from the news that his rank is ceremonial and he will not be seeing combat, after all.
One who is seeing combat, despite his efforts to avoid it, is Thomas Barrow whom Matthew recognizes in the trenches during a fierce bombing in France.
During a brief lull in the fighting, Thomas asks Matthew if he might still serve back home in the village's hospital instead. Matthew admits it would be difficult to transfer an able-bodied man from the front to do hospital work, regardless of his skill. When alone, Thomas heads to an isolated spot in the trench, holds his lit cigarette lighter aloft and deliberately takes a disabling injury to his hand that will be his ticket home.