The motivation for this two-hour PBS special is no mystery, and the only thing that’s afoot is a patently obvious exercise in cross-promotion. PBS presents Masterpiece Mystery!, which has a new season of Sherlock returning next year – so why not spend two hours celebrating Sir Arthur Conan Doyle’s famous literary creation as the father of modern forensics? Well, because that’s far too much TV time to assert a simple point – and, besides, it’s arguable as a post hoc fallacy of the greatest order. There’s some interesting information on hand here, making this a more watchable, and less reprehensible, promotional exercise than NBC’s Dracula-pushing Why We Heart Vampires. But still…  Check local listings.