Like everyone who loved the previous series of this magnificent hit reboot of the Sherlock Holmes stories, I sat down to watch the latest with some trepidation.

How to dispense with the swimming-pool face-off with urbane, unhinged just-this-side-of-camp criminal genius Jim Moriarty (an eye-catching Andrew Scott, The Hour)? The answer: with considerable aplomb and a rich comic seam.

Based on Conan Doyle’s A Scandal in Bohemia, this episode introduces Irene Adler (Lara Pulver, Spooks), who, for Sherlock, ‘eclipses and predominates the whole of her sex’, as a savvy, stylish dominatrix and would-be blackmailer with an incendiary client list. 

After a precipitous, hilarious and nearly naked summons to Buckingham Palace involving the theft of an ashtray, this pacey adventure rattles along with sharp, quick-fire dialogue, while remaining faithful to details of the original story. Part of the fun for those familiar with the stories is spotting how exactly these details might be interpreted for modern day London, but Sherlock works as a detective procedural even if you’ve never read any of the books. The dazzling but sociopathic protagonist is now so familiar an archetype through the likes of House, itself a reworking of the Holmes canon, and sunnier, sillier offspring, The Mentalist.

Sherlock’s place amid contemporary crime fiction allows a moment of affectionate satire of the genre’s conventions, too. On the way to a dramatic reveal set at landmark Battersea power station, John grumbles about the characters’ wholly unnecessary predilection for a little theatrical flourish. That little flicker of self-awareness, distracting in any other drama, works well here with Sherlock’s well-tooled mix of humour and thrills.

For all that, Benedict Cumberbatch’s performance in the lead is balanced, resisting the temptation to overtly display emotion in a character who would make every effort to hide it if any exists, or conversely to play Sherlock as an automaton. Sherlock’s inability to function in simple social situations if not in disguise isn’t just trotted out for laughs; a scene in which he inadvertently humiliates a blameless guest is excruciating and heartbreaking, but perfectly judged to illustrate a central fact of his character.

Better still, the easy chemistry between the leads shows no signs of flagging, making the central relationship utterly convincing. Writer Stephen Moffatt (Doctor Who) once again has his fun both with the deduction game, and with the prevailing assumption that men who live and work so closely must be gay. Moffatt indulges in more gleeful torpedoing of John Watson’s attempts at a love life, with mischievous suggestions of at least a little self sabotage. In an effective departure, Watson continues as a tough, capable and complex personality in his own right, rather than the undemanding duffer of the novels and stories.

The details which made the first series slot in seamlessly. John Watson (Martin Freeman) blogs about his adventures with Sherlock, which among other things provides opportunities for cheeky punning references to other Sherlock Holmes stories (The Speckled Blonde, anyone?) and for just a smidge of geeking out if you’re so inclined, especially when the deerstalker makes an appearance. Through some neat visual techniques, technology propels the story in other ways – Irene Adler and Sherlock circle one another using the written word, by text. a satisfying device for the characters and in building the world they inhabit. At the end od the story, instead of requesting a photograph of Irene to keep, Sherlock asks for her cameraphone.

Co-creator Mark Gatiss makes another welcome appearance as Mycroft Holmes, who delivers a number of delicious, revealing and bitchy digs at Sherlock, during their pleasingly childish sibling spats, as well as being a lynchpin about which major plot points turn. In all, A Scandal in Belgravia doesn’t disappoint: a breathless and brilliant start to the new series.