When Arthur Conan Doyle killed off Mary Watson, Dr. John Watson’s wife, in 1903, it was in such perfunctory fashion that he didn’t even mention her by name. In “The Adventure of the Empty House,” Watson is astonished to discover that Sherlock Holmes is alive, having thought him dead for more than three years. Holmes briefly details to Watson how he survived his fight with Moriarty at the Reichenbach Falls, and Watson muses on his friend’s return, and his reaction to Watson’s own state. “In some manner he had learned of my own sad bereavement, and his sympathy was shown in his manner rather than his words,” Watson writes. Thus was Mary dispatched: briefly, nonspecifically, and in a way that focused on Holmes, acknowledging his humanity while emphasizing his unshakable professionalism.

Conan Doyle’s axing of Mary was primarily utilitarian. He’d intended to retire Holmes and Watson as characters in 1893’s “The Final Problem,” killing off the esteemed detective, but fan outcry had obliged him to revive them. Possibly intuiting that the pair functioned best as roommates, without the distraction of Watson’s domestic life, Conan Doyle reunited them, which meant Mary had to go. The same reasoning seems to have been involved in the newest episode of Sherlock, “The Six Thatchers,” in which (major spoiler) Mary Watson died after pushing Sherlock out of the path of a bullet intended for him. “The reality of this, of course, is that Sherlock Holmes is about Sherlock and Dr. Watson and it’s always going to come back to that—always always always,” the show’s creator, Steven Moffat, told Entertainment Weekly. “They had fun making it a trio but it doesn’t work long term. Mary was always going to go and we were always going to get back to the two blokes. That’s the format.”

Moffat’s argument that killing off Mary was compulsory is a convenient one—it absolves him of any criticism regarding the decision to write out the show’s first substantial female character. (“[Sherlock writer-producer-actor] Mark Gatiss and I do not have the delusion that we know better than Sir Arthur Conan Doyle,” he opined in the EW interview.) Depending on how charitable you’re feeling, the assertion that Sherlock is rooted firmly in the Sherlock Holmes canon might explain the show’s other deficiencies when it comes to women and characters of color, and why its only nod to modern times seems to be technology. But it doesn’t fully stand up. Sherlock’s supposed adherence to Conan Doyle’s stories doesn’t limit the show when it doesn’t want to be limited—when, for example, it decides to invent a secret past for Mary Watson as a freelance assassin. And when it comes to other female characters, in fact, Sherlock has sometimes been even more regressive than its Victorian source material. It’s a paradox: Why does one of the most dynamic and ingenious shows on television have problems fitting women into its universe?

When Amanda Abbington’s Mary was introduced in the third season of Sherlock, her character seemed to immediately gel with the Sherlock-John bromance, enabling rather than impeding the show’s primary relationship. “I’ll talk him round,” she tells Sherlock (Benedict Cumberbatch), after John (Martin Freeman) has tried to throttle his friend for deceiving him for so long. Straightaway, she likes Sherlock—not most people’s initial reaction after meeting him—and seeks him out when she receives a mysterious text message that seems to allude to John being in trouble. Sherlock also accepts Mary surprisingly easily, winking at her when he remarks that weddings “aren’t really my thing.” The scene echoes Sherlock’s response to Watson’s engagement in Conan Doyle’s “The Sign of the Four” when he states, “I think she is one of the most charming young ladies I ever met, and might have been most useful in such work as we have been doing,” even while acknowledging that love is opposed to his preferred emotion, reason.

In Sherlock, Mary is a nurse at John’s medical practice but she isn’t subservient in any way, and Abbington’s spirited portrayal of the character made her a gratifying  addition to the show. In the final episode of the third season, “His Last Vow,” Sherlock extended the character further by making Mary one of the episode’s antagonists, revealing that she was a former assassin being blackmailed by a media baron with knowledge of her past. The fantastical (and soapy) twist not only defied the source material, it presented viewers with an intriguingly complex character—one with the ability to do awful things and remain sympathetic, much like Sherlock and John.

That Moffat would go to all this effort to create such a textured interpretation of Mary Watson only to kill her off to make room for Sherlock’s central relationship is a little baffling. Especially given that—unlike her literary counterpart—Mary gave birth to a daughter, and a baby isn’t the most conducive element to the adventures of two freewheeling bachelors. The more likely explanation is that Mary was killed to provide narrative momentum and conflict for a show that had otherwise stalled. As a dead wife and mother, Mary fits into the trope of a Lost Lenore, a character whose loss provides impetus for grief, anger, and revenge. While Conan Doyle’s Watson recovered from the loss of his wife in the space of a single sentence, the death of Abbington’s Mary has prompted a rift between Watson and Sherlock, widened by Watson’s guilt over his hinted infidelity.

This isn’t the first time the show has taken an intriguing female character and used her to propagate stale gendered archetypes. The first episode of the second season of Sherlock revolved around Irene Adler (Lara Pulver), a dominatrix who blackmails her clients and trades state secrets with Holmes’s nemesis, Moriarty (Andrew Scott). The character appears in the 1891 story “A Scandal in Bohemia,” in which she’s an actress who possesses a compromising photograph of herself with a European king, who is about to be married. As in the Conan Doyle story, Pulver’s Irene captivates Sherlock and challenges his perceived ideas about women. But in the show she’s a manipulative foe who uses her naked body to provoke him, and who has to be rescued from certain death, losing her battle of wills with Sherlock because of her feelings for him. In the original story, though, she’s simply a performer who hangs onto the photograph for her future security, and who ultimately outwits Sherlock. “He used to make merry over the cleverness of women, but I have not heard him do it of late,” Watson writes.

The transformation of Adler from Sherlock’s intellectual equal into a beguiling victim was immensely disappointing to some female fans of the show at the time. “The modern Irene Adlers are morally bankrupt puppets deploying their sexual wiles to lead men into the power of an infernal master—and are justly punished for it,” Esther Inglis-Arkell wrote for io9. “That goes all the way back to Eve.” This same sense of culpability was echoed in “The Six Thatchers,” in which it was insinuated by both Mary and Sherlock that Mary’s death was inevitable given her former career. “My old life, it was full of consequences,” she explains in her posthumous video for Sherlock. “The danger was the fun part, but you can’t outrun that forever.” Mary is gravely punished for doing what she loved and what she was good at, while Sherlock and John carry on largely unscathed.

It remains to be seen if new female characters will present themselves in season four. There are possible depths to “E,” John’s mysterious new contact (she’s played by Sian Brooke, who played Ophelia opposite Cumberbatch’s Hamlet at the Barbican in 2015). There have been hints about another Holmes sibling, with Mycroft (Gattis) asking to speak to “Sherrinford” at the end of “The Six Thatchers.” (Sherrinford is a hypothetical older brother to Mycroft and Sherlock who doesn’t appear in Conan Doyle’s stories, but who’s appeared in derivative works by other writers.) It would be counterintuitive (and gratifying) if “E” turned out to be Enola Holmes, an extra-canonical sister devised in stories by Nancy Springer, but it’s unlikely. Moffat is notably touchy about feminist criticism of Sherlock. Some have interpreted the mob of suffragettes wearing KKK-like hoods in the 2015 Sherlock Christmas special “The Abominable Bride” as an allegory for the pushback the show received for its interpretation of Irene Adler.

For now, the series’s primary female characters are Mrs. Hudson (Una Stubbs), Baker Street’s landlady, and a former stripper and cartel moll, and Molly Hooper (Louise Brealey), a pathologist whose help Sherlock relied upon in “The Reichenbach Fall.” Brealey’s character is notable in that she’s entirely original—she was reportedly only intended to appear briefly, but Moffat liked her performance so much that he kept Molly around. Although her primary characteristic is her unrequited love for Sherlock and a resulting string of bad boyfriends, she’s a smart, intuitive, and realistic woman, sensing Sherlock’s emotional pain at being tortured by Moriarty before anyone else. Molly proves that women can be flesh-and-blood characters in Sherlock, ones that add to the dynamic of the central twosome rather than diminish it. It’s a shame Mary wasn’t given the same opportunity.