The Earl Robert has confided to his mother that not only is his world shattered by the death of his daughter Sybil but also his marriage is broken. The tipping point has been that Cora blames his patrician ways for allowing the elite medical doctor's opinion to prevail. As a result, Cora believes, Sybil was not taken to the hospital for a C-section. Post-childbirth, Sybil dies. Cora believes the C-section could have saved her.
Grandma confers with the more enlightened doctor and persuades him to frame the C-section as providing a slim, very slim, possibility that Sybil might have lived. This framing, of course, lessens blame considerably.
Grandma invited the Earl and Cora over. The enlightened doctor presents the scenario of very little hope that Sybil could have been saved, even with a C-section. The Earl and Cora embrace, sobbing in each other's arms. Mission accomplished.
But that does not stop the old order from crumbling around the Earl. He commands his family to leave Mrs. Crawley's house because the former prostitute Ethel is serving lunch. They refuse, defying his order. The only one who sides with the Earl's point of view is Mr. Carlson.
In addition, Matthew has big plans for how to conserve money. He has made it clear that unless the estate is managed differently the money will soon run out. The Earl will have to cave to this. His daughter Edith will likely take the job as guest columnist at the newspaper which he sees as not in keeping with her aristocratic background. Also, the family is siding with Thomas to have Sybil's baby baptized Roman Catholic. The Earl stands alone in objecting.
Part of the changing of the old order is sadly that Mr. Bates, the former butler who is being released from prison, may not have a job at Downton Abbey when he returns. That's shown in the coming attractions.
But the marriage between Mary and Matthew is holding together during all this transition. Mary, along with Mama, is the female authority figure at Downton Abbey and she will have to come to support Matthew in his "turnaround" of the business of the country estate.