At dinner, there's talk of the upcoming luncheon for the tenant farmers, and Mary's having a hard enough time dealing with her feelings and Carson's inscrutably pointed looks before Edith says she won't be able to preside as she'll be in London, and the Dowager Countess turns to her. Mary balks, but the Dowager Countess goes on that should anything happen to Lord Grantham, Mary will have to run Downton until George is of age, and apparently no one before has raised this very practical point given that Mary complains that they need to shut up; her husband survived the war only to be killed in "a stupid car crash," and meta-commentary on plot twists necessitated by actor departures aside, it's hard to blame her for slamming out of the room. Lord Grantham sniffs that this is exactly what he was afraid of, but frankly such vehement emotion is probably a step forward, and the Dowager Countess agrees with me as she tells her son for not the first or last time that his head is up his noble ass, although she doesn't use anywhere near such language in front of the staff. She then changes the subject by raving about the mousse, so I guess the eggbeater is here to stay.
Molesley the Younger is looking up at the moon when his father joins him; son tells father that he's not sure where he's going and then complains about Lady Shackleton before he's even met her; he's doing so, we're to understand, because Downton and the Crawleys are the best, but given that he isn't so much, it's hard to take him seriously. His father is basically like, suck it up, kiddo.
Upstairs, Mary is lying on her bed when the Dowager Countess enters and tells her she's leaving. Mary supposes the Dowager Countess thinks she behaved badly, but the Dowager Countess emotionally says that she's not her governess but her grandmother, and as such, she loves her. This finally penetrates Mary's shell of self-pity, and the Dowager Countess takes the opportunity to say that she's been through hell, but now she must remember her son. Mary acknowledges that he needs her, but she's not sure she's going to be a good mother, as all the softness Matthew found in her "seems to have dried up and drained away. Maybe it was only ever there in his imagination." I mean this as a compliment, Mary, so forgive me for saying that's hogwash. The Dowager Countess doesn't go that route, but she does say there's more than one type of good mother and the fact is that Mary must choose between death and life. She puts an arm around Mary and it's a bad thing to say on a show where even young people die all the time, but I don't know what this show would be like without this almost-eighty woman.