December, 1924. Lord and Lady Sinderby invite the Granthams to the country estate they have hired for driven grouse shooting; their snobbish butler Stowell (Alun Armstrong) resents serving Tom and tries to ignore him. He is also rude to the other servants, who conspire to take revenge. When Thomas is insulted by an irate Lord Sinderby at the dinner table, he learns a dangerous secret from a tipsy Stowell, and arranges for his lordship's former lover and illegitimate child to arrive. Rose defuses the situation, earning her father-in-law's gratitude and respect. The Dowager Countess reunites Prince Kuragin and his estranged wife, and negotiates the continuing sparring between Spratt and Denker. Carson and Mrs Hughes search for a B&B to run together, but Mrs Hughes reveals she has no money, having spent all her savings to care for her mentally disabled younger sister Becy; Carson reveals he has bought a property in both their names. He then proposes marriage to Mrs Hughes, and she accepts. Isobel declines Lord Merton's earlier marriage proposal, not wanting to come between him and his sons.
A second footman is engaged: Andy, the temporary one they had in London, much to Thomas' delight. Robert learns he has a stomach ulcer, which will curb his drinking. Tom finally tells Edith that he has guessed that Marigold is her daughter, and Robert accepts her into the family. However, Mary is still unaware of Marigold's true identity as her youngest niece. Bates writes a letter confessing to have attempted to kill Mr.Green, and disappears, apparently to Ireland. Molesley and Baxter take a photo of Bates to different pubs in York, and find the one where he had lunch on the day in question, proving he was not in London when Green was killed. The witness who identified Anna has become uncertain and she is released on bail. A big Christmas party is held for the Downton household, and Bates returns and enjoys a tender reunion with Anna.