Now retired from detective work, Sherlock Holmes is called on once again to do battle with occult forces. Members of the Diogenes Club are being killed systematically, among them Holmes's own brother Mycroft. Meanwhile, unrest in Europe is threatening to turn into all-out war, and London is riddled with German spies whose machinations could have far-reaching, apocalyptic consequences. New enemies and old are conspiring against the great detective, and the stakes have never been higher. With trusty Watson once more at his side, Holmes sallies forth one last time to defy the nameless, unspeakable entities from beyond who would wish to conquer the earth and make every human their slave.