Set in December 1919 and January 1920. The household is bustling with all the Christmas preparations. The servants are having luncheon in the servant’s hall and Sir Richard Carlisle questions why they do not serve lunch upstairs as usual. Edith inquires whether or not Sir Anthony is invited for the New Year’s Day shoot. Rosamund had Lord Grantham invite Lord Hepworth who gets a disapproving look from the Dowager, who knew his father in her youth.
Matthew gets news that Lavinia's father is dying and he must go down to London. Miss O'Brien takes a Ouija board from Daisy and begins to play it in the servant’s hall. Meanwhile, Mary and the family are playing charades upstairs.
Lady Violet invites Sir Anthony to her house while Edith is there. He shows his injured arm to explain why he would not come to the shooting. Edith seems excited to see him.
After Lord Hepworth arrives, Cora receives a letter from Sybil with the news of her pregnancy. Lord Grantham says they have “Crossed the Rubicon”. The family and servants toast the New Year. All the men go out hunting pheasant and Matthew extricates lady Mary from Sir Richard.
Mr Bates is put on trial for the murder of his ex-wife Vera. Lord Grantham and Mrs. Hughes testify, but Bates is not portrayed in a good light and the evidence for prosecution look much more convincing than for the defence. Bates is found guilty and sentenced to be hanged. Anna breaks down and decides that she will have to leave Downton if worst comes to worst. Matthew tells Anna there's still a chance to fight, and later the death sentence is commuted to life imprisonment.
Cora Crawley finally informs Lord Grantham on the missing detail about Lady Mary's engagement to Sir Richard Carlisle. Lord Grantham later speaks to Lady Mary and convinces her that she shouldn't marry Sir Richard Carlisle despite his threatening to reveal her dark secret regarding Kemal Pamuk. She decides that she will go to America and stay with her grandmother until the scandal blows over.
She then tells Matthew about Pamuk knowing that he'll have to find out eventually and is surprised to hear that Matthew isn't worried about it. After dancing with Mary for a while at the Servant's Ball, Mathew tells her that they both lived their lives in different ways and it's in the past. Finally, Matthew proposes to Mary, but only after she insists he get down on one knee. She then accepts.
- So far, this episode and the 2015 Christmas Special are the only two Downton Christmas Specials actually set at Christmas.
- Violet uses the phrase Mais où sont les neiges d'antan? quoting the French poem Ballade des dames du temps jadis. It literally translates to Where are the snows of yesteryear?, or more figuratively, Why does life fade so quickly?.
- Robert says that Sybil has crossed the Rubicon. Roman law at the time of Julius Caesar made commanding troops into Italian territory a capital offence. When Caesar had his troops cross the river Rubicon in 49BC, he was irrevocably committed to his actions, hence the origin of the phrase.