BBC

That’s it then. Sherlock has gone as quickly as it came. Quicker, maybe – it got off to a bit of a shaky start. But this third and final instalment of series 3 was right back on form. The much sought-after ‘actual plot’ that many lamented the absence of in previous episodes finally materialised. And there was a fabulous cliff-hanger to boot.

We finally got to meet the man belonging to the pair of icy blue eyes that stared out at us on New Year's Day as Watson sautéed on the bonfire: Charles Augustus Magnusson (a thrillingly evil Lars Mikkelsen), sole retainer of a gigantic amount of incriminating information on everyone he’d ever come across, and also a massive creep. When he wasn’t licking people’s faces, he was busy blackmailing the entire country. But not for much longer. Enter Sherlock.

A slightly squalid Sherlock, actually, hiding out in a drug den - supposedly for a case. ‘Don’t look in the bedroom!’ he ordered once he’d been dragged home and scolded by everyone (not to mention slapped a few times by the wonderful Molly, who hasn’t had nearly enough to do this series). Sherlock was clean, it turned out. So what was he hiding in the bedroom? Only the flirty Irish bridesmaid from last week! Watson’s incredulous response to this ‘relationship’ was priceless – Martin Freeman is the king of reaction shots. But Sherlock had morphine pumping through his veins soon enough, this time in hospital: he’d been shot. The culprit? None other than Mrs Watson.

Oh, Mary! What a dark horse, stringing us along in your jovial manner! We saw the word ‘liar’ on the screen alongside ‘bakes own bread’ when Sherlock first met Mary, but we chose to ignore it because she was just so nice. Yet suddenly here she was, putting a bullet through him. It was a clever twist, and credit to Amanda Abbington for making us invest so much in her character in just a few episodes that the big reveal, when it came, was a genuine shock.

A series of confrontations followed, amusingly interspersed with Christmas at the Cumberbatches (with Benedict’s parents reprising their roles as Mr and Mrs Holmes). It was thrilling, but perhaps not to the extent of previous finales. Two years ago, Sherlock was the sharpest thing on TV. This year it knew it, and veered dangerously towards self-indulgence a few too many times. But you can’t fault its intelligence. There were lines in this episode that wouldn’t have been out of place in a sitcom, but as always they were woven around a much darker story - in this case one that played to very current fears of surveillance and exposure. Beneath all the panache, Sherlock remains a beautifully crafted drama.

After a final rendezvous with Magnusson (in what appeared to be the Tellytubby house crossed with Kew Gardens), Sherlock was on a jet headed for certain death in Eastern Europe. Not again. But oh, how they toy with us! Just as the credits began to roll, a voice piped up: ‘Did you miss me?’ And there he was in all his mad glory: Jim Moriarty. As quickly as it had taken off, Sherlock’s jet was landing. Yes, Moriarty! We did miss you! Come back and engineer some real crimes! Blackmail and face-licking are one thing, but not a patch on the havoc you used to cause! Let’s just hope your mayhem isn’t another two years in the making.