A series of unexplained illnesses, in his parish of Salisbury, causes Reverend Gerald Dervish concern enough to travel to London to consult with Sherlock Holmes-but to Dervish's disappointment, Holmes seems uninterested in his case.
When Watson reads of Reverend Dervish's death, seemingly of natural causes, Holmes immediately takes up his case. The investigation leads to the foreboding and much feared Granholm Asylum where several people have been committed after falling inexplicably ill. Sherlock Holmes is convinced a connection exists between these illnesses, Dervish's death, and the Asylum. Why are perfectly healthy residents suddenly falling ill? What caused those affected to lose their minds? And how is the Asylum connected to these mysterious incidents? With little support from the local police, it falls on Sherlock Holmes and his faithful friend Watson, along with Lady Harmony, to uncover the truth--a truth which might end with one or more becoming the newest inmates of the Granholm Asylum...