Sherlock: The Six Thatchers

"Don't you dare! You made a vow!"

Oh my. Well, spoilers abound, obviously. You have been warned.

The episode starts out so light-heartedly. There's a nifty cover-up for Sherlock so he can not go to prison, and he's all happy and stimulated in the knowledge that Moriarty is back. Sherlock even seems to be channelling Matt Smith's Doctor for much of the first part of the episode ("Are those ginger nuts?"), and there's much fun to be had throughout. Hence the shock at the end. But let's look st the whole episode as Mark Gatiss has utterly outdone himself with a superb bit of telly.

It's fun seeing Holmes rush through a fun series of cases in what has become typical Sherlock style, with John's blog superimposed on screen, all the wit and fun of the birth of little Rosalind and the addition of a baby to the dynamic, and especially the way that John and Lestrade manage to bond by taking the piss out of Sherlock. And then, almost in the background, we're introduced to the busts of the Evil One that give us our modern version of The Six Napoleons. At first this isn't foregrounded but, after a bit of fun with Toby the uncooperative bloodhound (never work with children or animals) we discover that there are six of them, made in Tblisi. And I for one knew, having read the short story, that the significance was likely to be the contents of one of the statues. But that isn't the twist; the twist is that this isn't to do with Moriarty at all, or the magnificent red herring that is the Black Pearl of the Borgias. It's about Mary's past.

We get a flashback to an embassy hostage rescue gone wrong, with one of the four agents being Mary and another being our antagonist whose name, we learn, is Ajay. And Ajay seems to think that Mary is a traitor and wants her dead. That's awkward. Yet Mary denies this to Sherlock and, after a fun few scenes in which she tries to leave for exotic shores to sort it out herself, she ends up explaining herself both to Sherlock and an understandably peeved John. Poor Ajay ends up dead but it seems that Mary is not the "Englishwoman" who betrayed them all. So who was it?

What is awful, and will of course become even more awful, is that John has been exchanging sexy texts with another woman, and it's even left ambiguous whether he's had an affair. All this while Mary thinks he's perfect. So the final scene arrives and the baddie turns out to be Vivian Norbert, the secretary- and we have, obligingly, been provided with a few clues to that effect. The crime is solved, the case is over- but Sherlock can't resist gloating over his adversary and, horribly, Mary ends up taking a bullet for him, and John's whole world with it. And the guilt must make it even worse.

So we end up with John cutting Sherlock out of his life utterly even as Mary implores Sherlock from beyond the grave to "save John Watson". The gloom is leavened only by a neat little reference to The Yellow Face and Mycroft making a call to "Sherrinford"....

That was good. Sherlock is back.