If I thought this would come as a shock, I'd suggest you sit down, but you know her as well as I do so surely you won't be surprised to learn that Mary read Matthew's letter. She explains that she felt destroying a man's last words without reading them was wrong, and while I don't necessarily doubt her, it's hard to take her completely at face value when she has so much invested in the letter changing Matthew's mind. Of course, I'm not just talking about the money, but about getting him to shut up about FEELINGS, so whatever Mary's reasons, I'm on her side. (Again, I don't expect anyone to faint over that revelation.) Mary asks Matthew if he wants to know what the letter said; hilariously, when he says no, she takes it as a yes and tells him that for a start, Lavinia wrote to her father the day she died -- remember she took a sudden turn and went down very quickly -- and that it was after she'd talked with Matthew about calling off the wedding and he'd refused. Matthew can't believe A) she wrote, given that they didn't find a letter or B) that she would have said those things, but Mary produces the father's letter and quotes, "She loved and admired you for this sacrifice of your own happiness, and she commended you to my care." The letter goes on to say that this prompted the father to add Matthew to his list of heirs and while he expects one of the other two to outlive him, should the money come to Matthew, "know it is with my full knowledge of what transpired." It finishes in this vein and Matthew looks like he's being prodded with the fireplace poker the whole time; when Mary's finished, he wheels around and asks if perhaps she wrote it. He then withdraws that accusation, but thinks that someone forged it and as many times as I've said that he needs to get over himself, I will admit that the letter is awfully suspicious, given how it is precisely what Matthew would need to hear in order to keep the money. Then again, Lavinia's father must have met Matthew and if he were going to leave him an estate of this magnitude, it must have been small enough bother to write a "Just In Case the Boy Loses His Damn Fool Mind" letter to make sure it doesn't end up paying for some Manchester city expansion. But, jokes aside, we know Matthew saw Lavinia's father on his deathbed; it's not the sort of thing he might have mentioned?
Carson comes in to see Mrs. Hughes and, with the subtlety of one of your smaller anvils, points out that it's late and asks if there's anything he can do. When she tells him she's just finishing up, he turns to go back out, but she asks him -- rather directly for these two -- if he said anything about her to Lady Cora. He's like, um, that all depends, but she puts him at ease by saying Lady Cora was so very kind and even though she doesn't worship the upstairs crowd like he does (Carson: "I wouldn't put it like that"), she freely admits she was quite touched. Having said her piece, Mrs. Hughes turns back to her work, but when Carson's gone, she looks up and there are tears in her eyes, but maybe she feels a little bit safer regardless.