Sherlock, Series 4, BBC One

Sherlock’s back in the here and now, and not before time. Twelve months ago, Benedict Cumberbatch’s Holmes laid down his mobile phone to return to Edwardian London for a plate-spinning deer-stalking mind-warping one-off. The Abominable Bride, though good in parts, caused a mass outbreak of head-scratching.

It now looks as if they thought so too. The fourth series began with a story that, by Sherlockian standards, played a unusually straight bat. It began at the beginning – the death of a Tory MP’s son – and took a relatively untortuous path to a clear end and another much more significant death. And flirted along the way with gung-ho ordnance-enriched action sequences.

Let’s leave it to Conan Doyle scholars to tick off the overlap between The Six Thatchers and its source material, The Adventure of the Six Napoleons. The little Frenchman was name-checked as a figure from the history to which Britain’s first female PM has now also been consigned, but mainly Mrs T’s role was tantamount to a red herring. A series of little busts of her kept getting smashed up and down the land. The trail led to Tbilisi where, six years earlier, an attempt to rescue the kidnapped UK ambassador was foiled with disastrous long-term consequences.

Mark Gatiss, who wrote the script, took it as a springboard to explore the murky past of John Watson’s enigmatic missus. Mary’s former career as part of a crack quartet of armed freelance operatives was revealed just as she began warming to the task of late motherhood (the baby girl, with a sense of drama to match that of her new godfather, arrived in the car on the way to hospital). The episode gave Amanda Abbington (pictured) a belated chance to stretch her legs, steal scenes and muck about with toys and wigs, and she grabbed at it as if coming up for air.

As a third wheel who upset the detective-sidekick dynamic, from the start Mary was a curious and not always popular addition to the Holmes narrative. In this episode John (Martin Freeman) was even able to cede his place in Baker Street opposite Sherlock to a balloon with a smiley face on it without being missed. Well, there’s no need to worry about her getting in the way any more.

If there was an intensely gloomy ending to The Six Thatchers, most of what preceded it was a familiar firework display of witty riffs and beguiling tricks. Gatiss’s narrative rhythm, abetted by director Rachel Talalay and Cumberbatch's ability to speak polysyllabic paragraphs at warp speed, is an amphetamine-powered quickstep, very occasionally interleaved by pit-stop scenes in which everyone is allowed to breathe a bit. Sherlock never gets less motor-mouthed, but more and more he plays on his reputation for matchless deductive reasoning by just making stuff up – about the mathematics of possibility, say, or Moriarty destabilising the US presidency (hah!).

Another of the pleasures of this new series is its comparative modesty. Since the third series two years ago, subscription channels have established new norms for appointment-to-view TV drama. If Sherlock were made by Netflix they’d hurl so many dollars at production design that you wouldn’t be able to hear the bangs for the whistles. The BBC's terrestrial version places most of its eggs in the baskets marked dialogue, plot and ironic running commentary. Hence the delightful scene in the London Aquarium in which Marcia Warren’s piffling secretary was exposed as an unlikely double agent. Never mind the outrageous implausibilities, nor things like Sherlock’s slightly naff pool fisticuffs with Sacha Dhawan’s rogue nemesis. Sherlock is content to look and behave like great television rather than television that thinks it’s on a 30-foot screen. 

The bum note was John’s bus flirtation that felt like an awkward offcut from Fleabag. What he needs saving from is the sidelines. Knackered dads flirting by text and other tawdry reminders of the everyday really don’t belong in the parallel hyper-reality of Sherlock. Unless there’s a twist, of course. There usually is.

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@JasperRees