It is the autumn of 1880, and Dr. John Watson has just returned from Afghanistan. Badly injured and desperate to forget a nightmarish expedition that left him doubting his sanity, Watson is close to destitution when he meets the extraordinary Sherlock Holmes, who is investigating a series of deaths in the Shadwell district of London. Several bodies have been found, the victims appearing to have starved to death over the course of several weeks, and yet they were reported alive and well mere days before.

It’s the autumn of 1890, and a spate of bombings has hit London. The newspapers are full of fevered speculation about anarchists, antimonarchists and Fenians. But one man suspects an even more sinister hand behind the violence. Sherlock Holmes believes Professor Moriarty is orchestrating a nationwide campaign of terror, but to what end? At the same time, a bizarrely garbed figure has been spotted on the rooftops and in the grimy back alleys of the capital.

It’s December 19, 1931. Hercule Poirot and Inspector Edward Catchpool are looking forward to a much-needed, restful Christmas holiday, when they are called upon to investigate the murder of a man in a Norfolk hospital ward. Cynthia Catchpool, Edward’s mother, insists that Poirot stay with her in a crumbling mansion by the coast, so that they can all be together for the festive period while he solves the case.

A series of grisly murders rocks London. At each location, only a jumble of bones remains of the deceased, along with a bizarre sphere covered in strange symbols. The son of the latest victim seeks the help of Sherlock Holmes and his former partner, Dr. John Watson. They discover the common thread tying together the murders. Bizarre geometries, based on ancient schematics, enable otherworldly creatures to enter our dimension, seeking to wreak havoc and destruction. 

The iconic duo find themselves swiftly drawn into a series of puzzling and sinister events: an otherworldly stone whose touch inflicts fatal bleeding; a hellish potion to unlock a person’s devilish psyche; a fiendishly clever, almost undetectable method of revenge and many more—including a brand-new Cthulhu Casebooks story.