When Professor Moriarty escapes the gallows - literally in a puff of smoke - Sherlock Holmes finds himself once again in pursuit of his old nemesis. Soon after the escape, Holmes' brother Mycroft asks him to work at identifying a leak in British Intelligence. Uncharacteristically, he refuses to help until he realizes that Moriarty is behind the missing State secrets. He learns that a very seductive woman, Sophy DeVere, has been hypnotizing one of Mycroft's young assistants to steal the information. When Moriarty is unable to decode the secret message he has stolen, he kidnaps Mycroft in order to get the information.