The first and, to date, only one-off special in the Sherlock series, The Abominable Bride takes place between some key events in the new Sherlock cannon. It follows on from 'His Last Vow' at the end of Series 3 where Holmes had killed the "Napoleon of blackmail" Charles Augustus Magnussen in broad daylight. His punishment? A suicidal assignment overseas, but this plan is almost immediately curtailed when a video is broadcast across the whole of London with Jim Moriarty's face asking "Did you miss me?"
So is Moriarty really alive after all and up to his old tricks? To find out, Sherlock enters his mind palace to confront a case from the past that might have an important connection. In the 1890s, a bride who had shot herself in the head appears to have committed murder from beyond the grave. If Sherlock can solve this unearthly conundrum, maybe it will shed some light on Moriarty similarly 'rising from the grave' after shooting himself, as it appears he has done.
What follows is an adventure in the Victorian era filled with cunning twists and turns and, finally, some answers to the deathly dilemma from the past and the riddle of Moriarty's return in the present.