In Thomas Harris’ The Silence Of The Lambs, Hannibal Lecter tells Clarice Starling “Nothing happened to me […] I happened. You can’t reduce me to a set of influences.” It’s an elegant, invincible line, one that waves away the tricks of their trades as psychiatrist and FBI agent, and paints Lecter as pure evil. Twenty-five years later, Harris scrapped all that to explain in Hannibal Rising that Lecter is what he is because Nazis ate his sister. Attention-grabbing? Yes. But about as elegant and invincible as a National Enquirer headline. A-to-B diagrams explaining the precise genesis of heroes and villains are likely to disappoint. Once you know the answer, what’s left to wonder about? Fans of detective fiction know that the pleasure comes from trying to solve the mystery, not having it all explained for us. The latest wheeze of writers Steven Moffat and Mark Gatiss is that Sherlock Holmes didn’t just happen, something happened to him. Namely, his little sister. Like Hannibal the cannibal, childhood family trauma made Sherlock the man he is today. Or rather, the man he was before A Study In Pink and John Watson’s friendship thawed his icy heart. And so The Final Problem reveals what we’ve really been watching these past six years: Sherlock’s gradual journey back to humanity. All you need is love. Da da-da da-da. All Eurus needed was love too. Trapped in her Mind Palace, she simply wanted her brother’s love, but, typical woman, instead of asking him outright, dropped hints, wrote him a coded song, flew a grenade drone into his flat, trapped him in the Crystal Maze of doom, invented a metaphorical plane, killed a bunch of non-metaphorical people and almost drowned his best friend. Appearing to have the resources of a Bond baddie and the mutant powers of all the X-Men combined (we never saw her sprout wings or grow blue fur, but I’m sure she could have if she’d wanted to) Eurus made a fair supervillain. Her comic-book name? Intellecto perhaps, or Professor E. The speed of her transformation from evil genius to vulnerable child though, was this episode’s toughest sell. As soon as Sherlock solved her cry-for-help riddle and bounded up those stairs her malevolence powered down so completely that she could be trusted back in the same cell she’d effortlessly broken free of in the same prison-asylum she’d turned into her own personal human experimentation lab. That must have been some hug. He should have tried it on Moriarty and saved everyone a lot of bother. Up until Eurus’ 360, the episode’s liberties taken with logic were easier to ignore. (If she was so worried about Sherlock putting that gun to his head, why explode 221B Baker Street with him inside? Would a family really never mention a dead child? Just how good were the transport links to and from this island that she could skip about flirting on buses, giving therapy sessions and eating chips without Mycroft hearing of it, no matter how many people she’d brainwashed? We could go on.) And this was fun to watch. Fun and ultra-tense with a terrific, whooshing sense of momentum. It went like the clappers, held its breath, went like the clappers again, held its breath some more until you thought you might pass out with the dizziness (oh, Molly!), then crescendoed into a screaming climax where nothing much made sense but by which point there hadn’t been a dull minute. Director Benjamin Caron previously worked on several Derren Brown shows – fitting when you think about it. It was all handled with a minimum of visual tricks. In an ordinary episode, Sherlock’s flashy post-production effects are there to jazz up what are essentially scenes of someone sitting down and thinking. In The Final Problem, a big, heightened concept episode, all the thinking was done out loud and standing up. The action negated the need for too much visual interference; there was already enough going on. That included a horror-homage opening, an action-movie prison infiltration complete with patrolling henchmen and more ticking clock scenes in close succession than is medically wise. There were laughs too, courtesy of Mycroft’s Cornish fisherman (the reveal of which felt very League Of Gentlemen) and yet another (brilliantly entertaining) surprise appearance by Andrew Scott. That surely has to be the last time Sherlock pulls that trick. It could very well be the last time Sherlock pulls any tricks. There’s been a real sense of farewell about series four, not least in this episode’s many fan-pleasing moments. The mention of Victor Trevor, Sherlock remembering Greg’s name and Lestrade revisiting his line from the pilot to call Sherlock a good man received whoops from the audience at the public screening, as did the appearance of Mycroft’s John Steed umbrella-sword, an object Mark Gatiss has publicly coveted for the character for years and at last allowed himself. Mary’s video served as an epilogue for the whole show to date. Quoting John’s emotional graveside speech about the best and bravest men she’s ever known, it felt like a curtain call, a last bow to soak up the applause before they all go their separate ways. As well they might.