If one thing can be said about this season, it is that each episode had a riveting concluding twist that left fans craving more. With each episode, the intensity and the immensity of the cases became wider, stretching like a rubber band to encompass more and more material. The foreboding nature of the episode, with its twists, turns and tentative spark of familiar dark humor, built progressively in a way best experienced rather than described.

The Final Problem was an apt conclusion to this particular season, but also one filled with questions. First of all, there were the fan’s musings, as they speculated whether the final problem would in reality be the final problem encountered by the iconic duo, wrapping up the series altogether. Luckily, season 5 is in the works and was given as one of the reasons why Mary was killed off in the season premiere rather than the finale. If Mary had been killed later on, the altered dynamic between John and Sherlock would have had to have gone unexplored for another painful two years of waiting. 

In reality, the Final Problem was composed of several problems concerning external figures and led up to a personal dilemma from Sherlock’s childhood, all orchestrated by the newest female character to enter the world of Sherlock, Eurus (Sian Brooke). Costumed similar to the girl from The Ring with her cascading brown locks and flowy white nightgown, Eurus proved a force to be reckoned with. She was equal parts dangerous and intriguing, a character that would keep viewers at the edge of their seats, waiting to see what she would do next. Like Mary, Eurus is not a canon character from Arthur Conan Doyle’s novels, but one concocted by the writers as a plot device to stir up more drama on the hit television show. She masterfully guides John and Sherlock through her own series of challenges, coming off as exceptionally bright and unpredictable. Her scheming enabled the episode to have many of the epiphanies, the “aha” moments that make Sherlock iconic. Fortunately, based on how the season concluded, it seems the role of Eurus will likely transcend season four as a staple in the BBC phenomenon.