Previously: An Unnatural Arrangement.

As Rhys Ifans reprises his role as brother dear Mycroft, Sherlock makes a discovery and a grossed-out face, whilst the most famous horse of Holmes canon rears its beautiful head: Silver Blaze.

Yes, for goodness’ sake, Joan and Mycroft had sex. There. She said it. Something that wasn’t even so much as hinted at during the season premiere, Step Nine, but that very much happened nonetheless. And of course, Sherlock’s over-thinking it. Two consenting adults did what consenting adults occasionally do — and that’s not Sherlock’s problem. He doesn’t question Joan’s right to make her own decisions, more her actual decision to sleep with his brother. Hence the grossed-out face (kudos to Jonny Lee Miller for maintaining that expression for so long without cracking himself up). Being confronted with one’s siblings’ more… convivial pursuits is pretty much always served with a more or less unspoken, ‘ew.’ Or a very much spoken one, if you’re twelve. Or, as it is, Sherlock Holmes.

And, yes, the aftermath may be a bit awkward, considering who they are; and having a one-night stand thinking you’re not going to see the other again before a good long while has passed doesn’t lend itself to smooth sailing a lot of the time, much less when you’re, perhaps, not entirely sure it wasn’t a slightly stupid thing to do. Joan was probably aware that Sherlock would figure it out, but then, sleeping with his brother didn’t have anything to do with him.

There was no message.

Still, the fact remains, Joan and Mycroft like each other, and there’s great potential for a lovely friendship there. I doubt they’re going to reprise their ‘arrangement,’ as Sherlock called it — but it’s up to them. Well, up to the writers, and I wouldn’t begrudge them either decision. I’d also like to see Mycroft around more.

As we can see in this episode, Sherlock does care about his brother, loathe as he is to admit it. He chased Nigella away because she was only after Mycroft’s money, and he’s pleased now that Mycroft has no intention of forgiving her again for what she’s been getting up to. Of course, ‘annoyed’ wasn’t the reaction Joan was hoping for after Nigella blabbed about her ex’s illness, but Mycroft’s explanation was priceless.

Spot of Leukemia. Bone marrow transplant, I’m better now.

As with Aidan Quinn and Jon Michael Hill completing the Detective Quartet, the chemistry between this trio — this family, if you will — is exciting and translates very well on screen. I’m looking forward to seeing this angle explored further within this season, as I hope it will.

Next: Blood Is Thicker.