A series of grisly murders rocks London. At each location, only a jumble of bones remains, along with a bizarre bone sphere covered in arcane symbols. The son of the latest victim seeks the help of Sherlock Holmes and Dr. John Watson, who discover a common thread that ties together the murders—and the persons responsible. 
Bizarre geometries—based on ancient schematics—point to members of a secluded cult. These men and women build strange constructs that will enable other-worldly creatures to enter our dimension, seeking sustenance. They are gaining so much power that even Moriarty fears that his empire is at risk—to the point that he seeks an unholy alliance with his eternal foe.