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.