If Mr. Sherlock Holmes had been in the country when the Baker Street Irregulars stumbled across the mystery of the Captive Clairvoyant, then no doubt he would have given immediate assistance. But Mr. Holmes was in Switzerland engaged in a deadly duel of wits with his most feared opponent, the evil Professor Moriarty; and so the Baker Street Irregulars, the gang of ragamuffins who sometimes assisted Mr. Holmes in his investigations, had to rely on their own wits. It all began—and ended—in Trump's Music Hall, the theatre where Sparrow was employed, where the star of the show was The Amazing Marvin, Hypnotist Extraordinaire and Mentalist Supreme! But Marvin had a secret and sinister agenda.