[WARNING: This review contains SPOILERS for Season 4 of Sherlock. Thank you.]

Sherlock Holmes is used to being lied to and manipulated by his older brother. Dr. John Watson, too, has become used to the Machiavellian scheming that is part and parcel of dealing with Mycroft. Neither of them suspected, however, the depths to which Mycroft went in covering up The Holmes’ family’s darkest secret.

There is another Holmes sibling. The cleverest and most dangerous of them all. One whose actions as a child so disturbed Sherlock that he erased all memory of them from his mind. One whom Mycroft saw sealed away forever in the island prison of Sherrinford.

And now… they are at liberty. They were responsible for tempting John Watson with the idea of an affair. They were responsible for sending Sherlock off on an investigation with a woman he could never have met. And they’re somehow connected to the apparent resurrection of criminal mastermind James Moriarty!

Now, Holmes and Watson shall find themselves tested as never before. The game is afoot and the stakes have never been higher.  Will this case truly be their Final Problem?

If Sherlock‘s fourth series is – as the fans and critics speculate – truly its last one, this episode is a satisfying conclusion. It is not without flaws, with Steven Moffatt and Mark Gatiss (more likely Moffatt than Gatiss) overindulging themselves with the sheer number of improbable twists that the plot requires. Vexingly, there is little in the way of explanation once the twists are revealed.

While this is not exactly unheard of (we never did find out exactly how Sherlock survived the Series Two finale, for instance), it does ring false to the tone of the series. Previous episodes had given the viewers a fair chance at being able to solve the mysteries using Sherlock’s own methods. Here, the villain’s challenges are based around emotional manipulation more at home in a Saw movie than Sherlock.

Given that, it is a credit to the skills of the cast that they are able to sell the material as well as they do. Benedict Cumerbatch and Martin Freeman deliver powerful performances, as per usual and Mark Gatiss gets a chance to show a different side of Mycroft as he is thrust into a situation that is completely out of his control. The rest of the ensemble, in what is typical of the rest of Series 4, is largely wasted. The one exception to this is Louise Brealey as Molly Hooper, who has perhaps her greatest moment yet as the coroner with an unrequited crush on Sherlock.

The Final Problem is not the greatest episode of Sherlock. It is not even the greatest episode of Sherlock this series. Yet for all its flaws the ensemble manage to utilize the good moments in the script to gloss over the weaknesses. The final few minutes are a worthy conclusion, regardless of what came before.