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 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.

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.

In the summer of 1994, a workman at the historic mansion of railroad baron James J. Hill in St. Paul, Minnesota, stumbles on a long-hidden wall safe. When experts arrive to open the safe and examine its contents, they make an astonishing discovery. There, inside, is a handwritten manuscript bearing the signature of John H. Watson, MD. The manuscript contains the story of how Sherlock Holmes and Watson traveled to Minnesota to track a murderous arsonist - known only as the Red Demon - who is threatening both Hill and his Great Northern Railway.

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.