Right from the opening scenes of Sherlock, we realised something was horribly wrong. The rain fell outside, and John Watson was hardly able to utter the words within the confessional of the psychiatrist's couch. Eventually, he confirmed our worst fears - "Sherlock is dead" - and we, like John, had to recover our senses sufficiently to discover why.
In flashback, it seemed all was going so well. Sherlock was being feted for his uncanny ability to solve the unsolvable and restore order and justice throughout the land, super-hero style. He was enjoying unprecedented fanfare of reputation and celebrity, with only the circumspect Watson to remind him that he was "almost famous" and how the media could "turn".
Michael Scott and Benedict Cumberbatch as Moriarty and Holmes in the final showdown
Sure enough, into this sleuthy jamboree strolled a villain worthy of the big screen. With balletic poise and stillness, in "no rush" as he reminded the police, Jim Moriarty showed Keyser Soze-esque powers of transformation. His mastery of 21st-century precision and interconnectivity could only mean one thing - he had his very own Moriarty app, and with it he simultaneously broke into the Tower of London, the Bank of England and Pentonville Prison. He was happy to be caught, after all, he was the man with 'the key'. As he put it, "I own secrecy."
The ensuing trial was a treasure of a scene, from Sherlock's advice to the QC on exactly how she should be questioning him, to his deconstruction of the jury. Once again, an exasperated John was left asking "Do you think you can survive for two minutes without showing off?"
We had to enjoy this while we could because, from then on in, it all got much, much darker. Threats loomed in all forms, whether it was from eastern European assassins moving into the neighbourhood, the threat of Sherlock's reputation and credibility being lost, or something only slightly less menacing than Moriarty, an ambitious journalist with pigtails. Sherlock dismissed the latter with three contemptuous little words it would pain me to repeat here.
There was so much to enjoy along the way: the ever-deepening bond between Holmes and Watson; the expanding enigma of worthy adversary Moriarty; the beautiful curve of the violin under Sherlock's chin as he accepted his arch-enemy into his home without turning round; the jaunty pace of the forensic-fest as Sherlock uncovered the whereabouts of two kidnapped children, compared with the solemn repose of lab assistant Molly as she told him she recognised the same qualities in him as in her dying father - "the sadness in him when he thought no one was watching".
There were many pleasing twists and turns as, sure enough, the journalist and even off-stage elder brother Mycroft turned out to be as helpful as a pair of chocolate teapots. But what had been good storytelling gradually became great as Sherlock's final confrontation with Moriarty edged ever closer and the depth of his burden became fully apparent.
In the wrong hands, it could have been camp and silly once the pair of them got to the roof, as loyal Watson raced back in a London cab. Instead, it was testament to the acting skills of all involved that what transpired was clever, challenging and ultimately very moving.
Benedict Cumberbatch, particularly, offered up a level of acting almost messianic in its quality, and his power as he stood alone on the roof single-handedly finished any argument that TV remains cinema's poor relation.
But he was served by a quality of writing that does not come along like a bus. Watching this episode was like eating the final spoonfuls of a high-calorie cake - rich, dense fare that would be impossible to feast on too often, but one where the very sweetest tastes were saved for last.
This review was originally posted on 15 January 2012. 'Sherlock' Series 3 will be shown later this year.