Season 4 of Sherlock premiered on Masterpiece in January. Passport members can watch full episodes here.
We have all three episode titles for season four of Sherlock, and two of them hint at the near-death of the titular character. Episode two, “The Lying Detective,” gets its name from the Arthur Conan Doyle story “The Dying Detective,” in which Sherlock pretends to fall for a murder attempt. He pretends to be terminally infected by a booby-trapped package in order to implicate the villain who sent the package to him: Culverton Smith, who we know shows up in the new season of Sherlock, played by Toby Jones.
The third episode shares a name with the most infamous Conan Doyle story, “The Final Problem,” in which Sherlock supposedly dies at Reichenbach Falls after grappling with Moriarty. Conan Doyle wished to move on from writing Holmes stories and so killed off the detective, only to succumb to public pressure and bring him back eight years later. But Benedict Cumberbatch’s Sherlock already had his Reichenbach Falls moment, when Moriarty shot himself and Sherlock jumped off a building in the finale of season two.
So what could this Final Problem be? There is, of course, endless speculation, but one thing at least seems to be fairly certain. Even if Sherlock continues after this fourth season, it will be a while before we get more episodes. Both Cumberbatch and co-creator and writer Steven Moffat have hinted that more episodes will not be forthcoming for a good long time. This is a show that has taken two years between the airing of seasons, so who knows how long that will be.
We do know that season four will be darker, both from interviews with the creators and from the trailers that have been released. We still don’t know much about Mary’s shadowed past. Sherlock will confront his demons, presumably the drug habit that has become increasingly prominent.
And Moriarty, that principal demon, is back in some form. While Sherlock insisted in “The Abominable Bride” that his arch nemesis was dead despite the eerie broadcast of Moriarty repeating “Did you miss me?”, the villain continues to haunt the detective, as when Moriarty mentally shows up in Sherlock’s mind palace after Sherlock is shot in the finale of season three.
In lighter news, John and Mary will have their baby, and it's a good bet that Sherlock will have some uncomfortable interactions with the child. But he’s vowed to “always be there, always, for all three of you,” so he’ll be spending a lot of time with the infant.
There also seems to be another new companion in addition to the baby: a dog appears in two of the photos we have from the next season. Perhaps this has something to do with Redbeard, the dog from Sherlock’s childhood that is also Mycroft’s code word for Sherlock’s problems with drugs? After all, Sherlock used a memory of Redbeard to calm himself down after being shot in the season three finale, so maybe he’s decided to get another dog to keep himself happy.
Speaking of Sherlock’s past, will a third Holmes brother appear? Mycroft has already hinted there was one, with his comment “I’m not given to outbursts of brotherly affection, you know what happened to the other one.”
Finally, what about Molly Hooper? Though we’ve only caught a short glimpse of her in a trailer, she was the one person Sherlock cared for that Moriarty didn’t know about, thus allowing her to help Sherlock stage his death at the end of season two. Since Moriarty is such a looming presence in this season, even if he is dead, will Molly again be a savior to Sherlock? Her engagement to a Sherlock look-alike is off, and one of the trailers shows Cumberbatch saying “I love you,” so who knows?