Sherlock TV review: the show got hacked twice over the weekend

In one dizzy moment over the weekend, when the series finale of Sherlock (BBC1, Sunday) leaked online, you could be forgiven for thinking that shadowy forces in Russia were only getting started by meddling with the US elections; their real mission was the hacking of Sherlock. To judge from the response of its makers, who implored fans to avoid spoilers, it also seemed to represent a graver threat to global stability.

It may have been overblown, but that panic underlined something about the show that is a rarity now in television: Sherlock is an event. For the conclusion of its fourth series, it preferred to be seen on television, or, revealingly, on the big screen, where several cinemas offered simulcasts. The episode was called The Final Problem, but this fidgety, overwrought series has already had its share. Once fleet, wry and cheerfully eccentric, it has become bombastic and bloated, stretched somewhere between those two screens.

To watch Benedict Cumberbatch's Holmes and Martin Freeman's Watson propelled from the exploding windows of 221B Baker Street, in a special effect that required a few more cycles through the mainframe, it is hard not to laugh, and I can't imagine how perplexing it must have been for the cinema audience. Co-writers Steven Moffat and Mark Gatiss reach for Arthur Conan Doyle for inspiration, in title and some narrative substance, but the blow-out episode is a much more awkward attempt to adapt every conceivable film genre, as though seduced by the aura of its stars' careers.

That’s why, in the opening minutes, we get absurd slabs of disaster movies, film noir and horror, replete with dashing children, portraits weeping blood and scary clowns (if you know of an easier way to confirm that Sherlock has a mysterious psychotic genius sister, he’d like to hear it), and an ensuing plot, set on a secret island criminal asylum, presumably leased from a Bond villain.

Indeed, as Sherlock encounters his malevolently calm sister, Eurus (Sian Brooke, in a cell and performance borrowed from Hannibal Lector), solves life-or-death puzzles against various countdown clocks, and is routinely asked to kill one accomplice or another, every tortuous detail announces another detour from the strengths of the show. Good luck, television, Sherlock is going to the movies.

But just as the writers have stretched the canvas of this once-nimble show, they have decided to shrink Sherlock, in every sense. Here he is a figure of erased memories and submerged traumas, a once-emotional child who made himself an automaton. The mystery of The Final Problem is not the three-year flirtation of Prof James Moriarty's return from the dead. (It is daftly included, through flashback and recorded video commentary, for the pleasure of seeing Andrew Scott again; "I'm relatable that way," he says, in the episode's best line, as though trolling the studio.) Instead, the mystery is how Sherlock became Sherlock. Watson and Mycroft may urge the detective into "that deduction thing", but here, sadly, it isn't his reasoning that's on display – he is instead made to seem lesser.

People will come to argue about the precise moment Sherlock jumped the shark, and The Final Problem offers numerous details too goofy to forget: dangling men, gagged and bound, outside a window like prizes on a gameshow; an urgent disaster finally revealed as metaphor; flailing continuity inconsistencies that short-change the attentions of the viewer.

But the most egregious error is to try to solve Sherlock, something more fatal to the character than any fall. Those Russian leakers must feel redundant. Sherlock was already hacked.