Tonight’s episode gets deeper into the core backstory of Sherlock Holmes – and introduces the person from his past, a vicious and brilliant criminal, almost certain to be identified, eventually, as his arch-nemesis Moriarty. The episode title is a little cagey, but you don’t have to be Sherlock Holmes, or even Lucy Liu’s Watson, to guess the game that’s afoot. The title of tonight’s episode? “M.” Just don’t expect Peter Lorre. That’s an