A few years ago, the BBC declared that brainy was the new sexy. Forget martinis, girls and guns: the first three seasons of Sherlock triumphantly announced that brains were superior to brawn and proved it by turning a wry detective drama into an international hit. Unfortunately, the fourth season of the show has derailed the tale of the socially dysfunctional detective with his natty coat and violin. Rather than solving crimes, Sherlock has instead been burdened with the tropes of superhero films, more familiar to Bond and Batman than the boys of Baker Street. The result has been an identity crisis within the show.

The descent into spy clichés began with the revelation that Mary Watson used to moonlight as a Jason Bourne equivalent. Since then, the show has featured spies returning with a vengeance, underwater fight scenes, motion-sensor grenades, memory-wiping drugs, a top-secret prison and tranquilliser darts galore. Steven Moffat has also taken a page out of Christopher Nolan’s guide to creating antisocial anti-heroes. This season, Cumberbatch’s character has encountered repressed childhood traumas, an ancestral home burnt to the ground and villains with improbable powers. Does season five promise a Batman/Baker Street crossover?

“With a Yorkshire accent, strange teeth and a creepy manner around children, Toby Jones’ character only needed a cigar and tracksuit to complete the Savile allusions”

Sherlock’s crusade into the land of silly plot premises and over-blown characterisation culminated in the season finale, “The Final Problem”. The opening five minutes were lifted from a Hammer Horror, complete with portraits oozing blood and cleaver-wielding clowns. Eurus (Sherlock’s psychopathic little sister) then presented us with a pastiche of Anthony Hopkins’ Hannibal, manipulating her guards and refusing to blink on screen. Finally, Moffat landed our heroes in a maze of challenges – a sadistic cross between Saw and The Crystal Maze.

The genre-hopping, narrative-scrambling plots have damaged the show’s credibility. In previous seasons, each episode posed a seemingly impossible but sufficiently plausible challenge for Sherlock to overcome. The solutions were so brilliant and the scripts so witty that the audience could forgive the more outlandish elements (faked suicide theories, anyone?). However, this season ultimately bordered on silliness, as Moffat and Gatiss tried to escape the tangled web of plotting in which they had ensnared themselves.

How does Sherlock get away with murdering Magnussen at the end of series three? MI-Mycroft edits it out of history, of course!  How does John survive being shot in the face by his imposter therapist? It was a tranquilliser gun! How does Eurus escape her maximum security prison, pose as three different people (in the process carrying out a fully-fledged text affair with John), set up an elaborate death trap and return without anybody noticing?  Who knows? Just don’t think about it too hard. Most superhero plots only survive by avoiding audience scrutiny; it is a pity to see a show which once took pride in its intelligence resorting to the same plea.

 “Rather than solving crimes, Sherlock has instead been burdened with the tropes of superhero films, more familiar to Bond and Batman than the boys of Baker Street”

The real shame with Sherlock is that the vital components of a wonderful show are all still present. The famous wit remains, with some of the series’ one-liners among the best on TV. The imaginative brilliance of Moffat and Gatiss is always present, too. It is easy to forget that a scriptwriter has to think through each of Holmes’ observational ‘deductions’. They are no small feat of ingenuity and it is therefore a pity that they often feel rushed. 

Sherlock: The Empty Hearse

Above all, the show remains willing to be provocative and current. The second episode (arguably the season’s best) produced a genuinely stomach-churning villain: a depraved philanthropist, using his influence to murder patients in a self-funded hospital. With a Yorkshire accent, strange teeth and a creepy manner around children, Toby Jones’ character only needed a cigar and tracksuit to complete the Savile allusions - a bold move for the BBC. We can only hope that Sherlock’s producers are bold enough to return to their successful roots when, or if, a fifth season emerges