Set in July and August 1914. Cora Crawley discovers she is pregnant, which leaves Mary Crawley wondering how to answer Matthew's proposal since his situation would change completely if the baby turns out to be a boy. O'Brien is angry when she mistakenly believes that Cora is going to replace her and takes advantage of an opportunity to punish the Countess causing her to miscarry, only to induce further heartache when its discovered that the baby would have been a boy. Lord Grantham sends Mrs. Patmore to London to have cataract surgery. Anna goes with her and learns from Bates's mother that he took the blame for his wife's thefts. Gwen secures a position as a secretary and Thomas hands in his notice. Sir Anthony Strallan promises to propose to Edith at a garden party, but Mary manipulates him otherwise in revenge for Edith having revealed her affair with Pamuk. After her mother's miscarriage, Mary is prepared to marry Matthew, but he tells her he cannot be sure of her motives and says he will leave Downton. Lord Grantham announces that Britain is at war with Germany, marking the beginning of World War I.
Cora discovers she is pregnant. The family is astonished and, in London, Mary wonders how to answer Matthew’s proposal, since his situation would change completely if the baby is a boy. Her aunt, Lady Rosamund Painswick, questions whether Mary would be happy as the wife of a solicitor. Evelyn Napier tells Mary that the story going round about Mary and Pamuk was started by Edith.
In Downton, family and servants prepare for a garden party in aid of the local hospital. Everyone is delighted at the prospect of a new baby. Robert, however, is anxious to do the right thing by Matthew, who is already bitterly disappointed that Mary will not give him an answer until after the birth. Isobel discovers that, for a change, she and Violet are agreed on this matter. They both wish Mary would say yes. Mary accuses Edith of spreading the story that threatens to ruin her. Edith shrugs. Mary had it coming.
At Mrs Hughes’s prompting, Robert informs Mrs Patmore that he has arranged for her to see an eyespecialist in London. Anna will accompany her. Mrs Crawley’s cook, Mrs Bird, will look after them. Mrs Patmore asks Daisy to ensure Mrs Bird’s cooking does not surpass her own. Daisy takes her task very seriously.
O’Brien has received a letter. Thomas is thrilled with its contents and they show it to Carson who passes it on to Robert. It contains unfortunate news that O’Brien has dug up about Bates, and Bates’s future at Downton still hangs in the balance following his revelations in the previous episode. Robert informs Cora. He would prefer to get rid of O’Brien, rather than Bates, and he says it just as she walks into the room. O’Brien is angry at the thought of being replaced and the news motivates Thomas to enquire with Clarkson about finding work in the army medical corps. When Thomas tells O’Brien that Cora is advertising for a new maid, O’Brien’s rage makes her arrange an accident for Cora resulting in the miscarriage of her baby boy. But O’Brien is mortified when she discovers the truth. It was Violet, not Cora, who was looking for a lady’s maid.
Mr Bromidge is charged with fitting Downton’s telephone. The servants all wonder how it works. Bromidge is talking to Sybil about his trying to find a secretary. She immediately thinks of Gwen. Sybil enlists Branson’s help and ensures the job interview goes ahead without a hitch in the library.
The news of the death of Cora’s unborn son spreads quickly and Thomas’s callous comments bring a punch from William. The moment bonds William and Daisy. But when Mary tries to accept Matthew, she finds her delay in giving her answer before the miscarriage has cost her a husband.
In London, Anna delves into Bates’s history. She visits his former Barracks and gets an address for his mother who tells her the truth of her son’s past. Anna informs Robert who assures Bates that his job is secure. Despite this, Bates is still hesitant to reveal his true feelings towards Anna, but when Molesley makes an enquiry into Anna’s availability, Bates assures him she has a serious admirer.
Molesley sees Thomas attempting to steal a wallet from Carson’s coat pocket. Carson informs Robert and they agree to dismiss Thomas after the garden party.
On the day of the party, Mrs Bird and Mrs Patmore, having initially hated each other, find common ground in fighting Mrs Hughes. Before Carson gets a chance to sack him, Thomas hears from Dr Clarkson that he has a place on a training course at Richmond Camp. Instantly, he hands in his notice. Sir Anthony Strallan has promised to propose to Edith at the party, but a bitter Mary corners him first and destroys Edith’s chances. Mary has had her revenge for Edith’s treachery.
The telephone rings. Branson answers and learns that Gwen has got the job. He runs to tell her and Sybil, hugging each other and dancing, until Mrs Hughes’s sharp words put a halt to the celebrations. Mrs Hughes warns Branson that he stands to get his heart broken and lose his job.
Robert is handed a telegram, shocked, he announces: “Ladies and gentlemen,” he says, loud enough to be heard by all the company, “I regret to inform you that we are at war with Germany.”