Entities leak into the human realm and enter human minds. Two of the victims are Dr. Watson and leader of the cult, Prof. Henry Fitzgerald-who seeks to use human sacrifice to open the door to the Old Ones.

As violence erupts in London, Holmes secludes himself in the Diogenes Club, developing an antidote to counter the neural psychoses.

As Moriarty uses the drug to amass an army of addicts, Holmes discovers a link to a town in America. Innsmouth.