The instant Irene Adler's scarlet-tipped fingers extended across the frame on Sunday night, it seemed certain that Steven Moffat's rewriting of Sherlock Holmes's famed female adversary would cause some consternation. The series opener of Sherlock – watched live by almost 10 million people – updated Arthur Conan Doyle's A Scandal in Bohemia, the short story in which Holmes is, unusually, outwitted by an acute American adventuress in possession of a compromising picture of the Bohemian king. The woman Holmes referred to as "the woman" was remade by Moffat as a high-class dominatrix saved only from certain death by the dramatic intervention of our hero. While Conan Doyle's original is hardly an exemplar of gender evolution, you've got to worry when a woman comes off worse in 2012 than in 1891.

In many ways the Holmes stories are a perfect fit for Moffat's skill-set. The puzzle-box plotting, the 24/7 bromance, the fetishisation of "masculine" reason over pesky "feminine" emotion, all suit him right down to the ground. In the case of his stewardship of Doctor Who, Moffat's tendency to write women plucked straight from a box marked "tired old tropes" (drip/scold/temptress/earth mother to name but a few), and his consequent failure to sketch a compelling central dynamic between the lead and his companion, has seriously affected the show's dramatic power. But no such trouble with Sherlock.

Doctor Who has never just been about a dashing alien who happens to be wicked smart. The Doctor cares about stuff, and uses his considerable noodle to fight injustice, tyranny and exploitation. By contrast, Holmes is in it for no reason other than Reason. An insufficiently stimulating case will be summarily dismissed as "boring". A Scandal in Bohemia opens with Conan Doyle sidelining feeling as "grit in a sensitive instrument", a spanner in the works of the world's "most perfect reasoning and observing machine". Unlike Who – where, famously, the evil of the Daleks is linked directly to their rejection of human emotion – Conan Doyle paints a hyper-rational universe almost made just for Moffat.

In this context, what Moffat would do with Adler was always going to be interesting. From a certain perspective, Conan Doyle's character is something of a "proto-feminist", a woman of great intellect and formidable agency, who, above all, proves to be a match for Holmes. It's not unproblematic that both author and protagonist respect Adler only because she has a "soul of steel" and "the mind of the most resolute of men". She's not a waste of space, it is suggested, because she escapes the weakness of her sex and can act, symbolically, as a man. But, importantly, she makes her own way in the world. In the climactic scene of Conan Doyle's story, emotion initially leads her to betray herself, and – like all women – when confronted by danger, she protects the thing she cares about (which, according to Holmes, is invariably either babies or jewellery). However, after these events, having had time to reflect coolly, Adler realises she has given herself away and plans the escape by which she gets one over on Holmes.

However, even this ambiguous portrait of female power proved too much for Moffat to stomach. Granted, he allowed her to keep her smarts. But, at the same time, her acumen and agency were undermined every which way. Not-so-subtly channelling the spirit of the predatory femme fatal, Adler's power became, in Moffat's hands, less a matter of brains, and more a matter of knowing "what men like" and how to give it to them; of having them by the sexual short and curlies, or, perhaps more aptly, on a nice short leash. Her masterminding of a cunning criminal plan was, it was revealed late in the day, not her own doing, but dependent on the advice of Holmes's arch nemesis, James Moriarty. A move that, blogger Stavvers noted, neatly reduced her from "an active force to a passive pawn in Moriarty and Holmes's ongoing cock-duelling".

More troubling still, Moffat's Adler blatantly fails to outwit Holmes. Despite identifying as a lesbian, her scheme is ultimately undone by her great big girly crush on Sherlock, an irresistible brain-rot that leads her to trash the security she has fought for from the start of the show with a gesture about as sophisticated – or purposeful – as scrawling love hearts on an exercise book. As a result, Moffat sends Adler out into the world without the information she has always relied on for protection, having made herself entirely vulnerable for the love of a man. Lest we haven't got the point yet, Holmes hammers it home. "Sentiment," he tells us, "is a chemical defect found in the losing side."

And then there was the jaw-dropping finale, which somehow managed to smoosh together a double-bill of two of patriarchy's top-10 fantasies. All those troubled by female sexual power – or the persistent punctuation of orgasmic text alerts – were treated to the sight of the vamp laid low, down on her knees, about to have her block knocked off by a great big sword. And, at the same time, our hero miraculously appeared to save his damsel in distress. Medusa and Perseus, Rapunzel and her prince, all wrapped up in a potent little bundle. Symbolically speaking, it was really quite impressive. But for those of us crazies who like to think that women are, y'know, just regular human beings, it was, politically, really quite regressive.