England has barely recovered from the blow of the Circle of Seven when Mycroft Holmes receives news of an extremely strange crime. The Jarvis family has apparently been poisoned. Mycroft Holmes asks Professor van Dusen, who is currently visiting him, to take on the case. As the Thinking Machine begins to investigate the crime scene, Sherlock Holmes unexpectedly joins them. It seems that the great detective has been directed here by an unknown individual. Van Dusen and Sherlock Holmes set to work on the investigation, but the method of murder presents them with more than just a puzzle. They have little time to catch their breath as a second crime is already looming. It’s as if the unknown individual is playing a wicked game with them. And suddenly, this very person removes their mask right in front of them.