There is, of course, some movement on the tax plot: Mary went to London to talk to the tax authorities. She wanted to see how long they would allow her to pay the tax, and what scale. That is, if they’ll allow the estate to pay the £2 million over the course of 20 years, that’s just £100,000 (plus, presumably, interest) each year. While that’s still a lot of money, it’s much less burdensome than the full amount at once.
Of course, paying the tax in installments carries its own burden, in addition to interest: Lord Grantham mentions that he doesn’t want to be dragging the debt behind him for 20 years.
The show, sadly, didn’t tell us how the meeting went. I assume that’s just to whet our interest, and that tax will again be front and center next Sunday.
Now, if only Sherlock will include a tax subplot . . .