After the season four premiere received a mixed reception, Sherlock grabbed its audience by the throat in its shocking, emotional rollercoaster of a middle episode. Titled The Lying Detective, we had Sherlock going off the deep end, John broken with grief, a creepy villain and a massive show-stopping reveal. Last chance, people, if you haven't caught up with the latest episode yet, you're about to get spoiled.
In the episode's closing moments, we find out that John's bus lady mistress, fake-out Faith Smith and the German therapist are all the same woman - Sherlock and Mycroft's secret sister, Eurus. It's an exciting deviation from the traditional Sherlock Holmes story which will hopefully lead to an explosive season (possibly series) finale next week.
In other areas, however, this episode paid a lot of tribute to the work of Arthur Conan Doyle. Read on for 18 easter eggs, references and connections that you might well have missed in The Lying Detective.