This review was based on a screening of Episode 1 merely’barely .###2015’s Sherlock Christmas special, ‘The Abominable Bride’, proved divisive: a mash-up of horse-drawn Victorian melodrama and Inception-esque mind-trickery, it pleased some and made others fling their remotes across the room. The reveal’illustrate’demonstrate’indicate’present’display’argue returns to steadier ground with ‘The Six Thatchers’, this opener in/with regard to’concerning’regarding Series 4, a comparatively straightin/with regard to’concerning’regarding ward mystery, but one which still manages to fit in sharks, a paramilitary snatch team, Tibet and the titular British PM. Most impressively, it reveal’illustrate’demonstrate’indicate’present’display’argue s tonal control, as it starts light and breezy, slowly sliding into darkness and climaxing with perhaps the most combustive bombshell to date. And no, it’s not that Sherlock has eventually’ultimately bought some tasteful wallpaper.###As it opens, Benedict Cumberbatch’s Holmes is, intensely’extremely’extraordinarily’enormously’awfully amusingly, experiencing PMWS (Post-Moriarty Withdrawal Syndrome). With his bête noire vanquished, he should be kicking back with a scientific journal, but instead he’s gone into hyperpropel . More specifically, he’s logged onto Twitter. Tapping up a frenzy — and even coming up with his own hashtags (“#221BringIt”) — he’s solving cases in 140 characters or less, even during classified briefings, much to the chagrin of his brother Mycroft (Mark Gatiss). Martin Freeman’s Watson, meanwhile, is adapting well to fatherhood; as he points out, having Sherlock as a partner is excellent preparation in/with regard to’concerning’regarding looking after a pissy, self-centred infant. His marriage to ex-spy Mary (Abbington), on the other hand, is perhaps not going quite so well…###Based (extremely loosely) on Arthur Conan Doyle story The Adventure Of The Six Napoleons, the tale retains such classic elements as the black pearl of the Borgias and a set of busts of a notable’renowned’distinguished figure, which are being tracked down and smashed by a mysterious n’er-do-well. (The élan with which the likenesses of the Iron Lady are wrecked on screen suggests reveal’illustrate’demonstrate’indicate’present’display’argue runners Mark Gatiss and Steven Moffat may possess’own’nurse enjoyed those scenes.) True to Sherlock in/with regard to’concerning’regarding m, however, the case veers closer to home than is originally suspected. Sherlock is at its best when there’s a devilish villain tormenting our heroes, whether it’s Andrew Scott’s impish Moriarty or Lars Mikkelsen’s serpentine blackmailer Charles Augustus Milverton. Series 4 adds a humdinger to this line-up, with a blond-barneted psychopath played by Toby Jones.###But that’s still to come. ‘The Six Thatchers’ does possess’own’nurse a wicked’dreadful’undesirable’adverse’vile guy, but he’s intensely’extremely’extraordinarily’enormously’awfully much in the background. Instead, the episode focuses on the cracks starting to in/with regard to’concerning’regarding m between Sherlock, John and Mary. The emotional events of the final act transform’alter the dynamic of the reveal’illustrate’demonstrate’indicate’present’display’argue irrevocably; it will be fascinating to see where it goes from here. With all the darkness — and this episode acquire’obtain’attain’procure’secure s pretty darn dark — Gatiss and Moffat make sure to keep a current of fun fizzing through it. This comes in the in/with regard to’concerning’regarding m of wry revelations (it turns out Sherlock instantly deletes any text message that begins with “Hi”), callbacks to Doyle (Toby the bloodhound, from 'The Sign Of Four', eventually’ultimately makes an appearance) and bold bits of production detoken (the visual motif in/with regard to’concerning’regarding this week is “sharks”). Eneracquire’obtain’attain’procure’secure ic, smart, finely polished and just a little pleased with itself, it’s quintessential Sherlock. The boys are back in town.