Context: Post-war, Sybil is in Dublin with Branson, Mary is now married to Matthew, however Edith is still committed to Sir Anthony. The rivalry is high between the sisters while Sybil is in Dublin.
'"How could you have been so shameless? I thought a little better of you, you know." Mary resented, frenzied by Edith's limitless spite.
"A little less shameless than you, I think. Lady Mary, the harlot who took it up to throw herself at the first foreigner that ever came to Downton. Still, I can't say I thought any better of you." Edith sniped back.
They were in the small library and Carson had just walked out, Mary had pounced on Edith after a day of knowing her own sister had been the one to tell her husband about her affair with the Kemal Pamuk. How could Edith have found out? How could she have been so foolish herself, to get so wrapped up in such scandal only two years after her own coming out season, so many years ago. How could this have come back to bite her now?
Mary stood, glassy eyed and disbelieving at her rival for a sister. Edith stared back, every sign of a sneer was apparent from where she sat at the mahogany desk.
"You will hold your tongue if you have any sincerity left in you. Unless you admit to being such a petty, ruthless b***h."
"Matthew had a right to know."
"Heavens forgive me! What right had you to tell him?"
"All I know is that you were morally inclined to do so yourself, and you didn't."
"Just you talk about morality! Listen to yourself, you pathetic tyrant."
"At least I have honour."
"Do you?" And with that, Mary stalked out of the room, fuming.
"More than you at any rate." Edith scoffed to herself.