And that’s what Sherlock has become since it appeared on our screens. By its protagonist’s own rooftop admission, ‘It’s just a magic trick’, with each episode showing the impossible before explaining it with a grand hashtaggable ‘Ta-Dah!’ backed by great scripting, editing, and performance. Sherlock is the magician, John Watson his lovely assistant. We are the eager audience. Messers Moffat, Gatiss and Thompson have turned the art of detection into an illusion.

It’s a routine that works. Never more so than in ‘His Last Vow’, which was an outstanding act of drama. Perhaps the finest 90 minutes Sherlock has ever produced. And all because, amid the deductive illusions of false fiancés and bullet-time deductions, and a BAFTA-defining performance from Martin Freeman, it accomplished what its preceding two episodes didn’t.

From the crack-addled update of ‘The Man with the Twisted Lip’, to the mention of a third Holmes brother (a sure series 4 or 5 plot point there), it reconstructed the source material and then built on it. That it followed so closely to the original tale ‘Charles Augustus Milverton’ and yet still found so much to add is worthy of applause.

Lars Mikkelsen was truly repulsive as the Le Chiffre of secrets. From the moment he licked – LICKED! – national treasure Lindsay Duncan, we understood we were dealing with a Grotesque. A Nosferatu of knowledge. The Master Debunker. A man who bleeds his victims of their secrets and feeds upon them.

Against his reptilian repugnance, Amanda Abbington seemed just a little too nice, a little ‘afternoons on ITV3’ to be a rogue CIA assassin turned Mrs Watson, but maybe that was part of the illusion. And perhaps she’d had time to give Sherlock shooting lessons. Because Holmes, a killer? That’s new and, on appearance, uncomfortable. The character has never willingly killed anyone. Only time will tell how satisfactorily it sits within the show’s self-made canon. Or maybe it’ll be revealed as a bluff. A clever shot. Another magic trick.

Yet the greatest magic of ‘His Last Vow’ is that – against a series over hyper-edited, timey-wimey shenanigans – this was a plot that was easy to follow but also riveting. Hopefully that’s proof to the writing team that the two aren’t mutually exclusive.

And this being a finale, we all expected another death-defying cliffhanger. Turns out this time ‘the prestige’ is stolen from Sherlock. Moriarty’s seemingly back from the dead with a better ‘Howdeedodat?’ mystery than his rival. And a better hashtag. Well, that’s very him, isn’t it?

A new magic trick has begun and Britain is in peril. James Bond’s off drinking and shagging his way around the planet. We need a true British hero. A man with a coat and an assistant. A man who can pull, not a rabbit, but the East Wind, from his Deerstalker. We need Sherlock Holmes.

Hashtag that, magic fans.

Aired at 8.30pm on Sunday 12 January 2014 on BBC One.

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