I don't know if Tod Slaughter ever played Professor Moriarty on stage, but he should have. The role of a criminal mastermind is exactly the kind of role the actor relished in his films. The closest he came in his film career was as Michael Larron, the head of The Black Quorum in Sexton Blake and the Hooded Terror (1938, directed by Slaughter's long-time collaborator, George King). This is a stock series programmer, so no one should go into this expecting some kind of transcendent masterpiece. Hell, it's not even very good--just staying--but the idea of Slaughter as Moriarty is all kinds of delicious.
In truth, Larron the Snake is kind of an amalgam of pulp fiction supercriminals. Inspired by Moriarty, sure, just as Sexton Blake, his adversary, is a knock-off of Sherlock Holmes. But Larron also has elements of Sax Rohmer's Fu Manchu (there's an orientalism in his sartorial habits and employment of faux Si-fan underlings), and elements of a proto-James Bond villain. Slaughter plays this with surprising restraint, given the broad nature of the character and the actor's own tendencies. No mustache-twirling or hand-wringing here, though he has awesome facial hair for the role. On the other hand, once all pretenses fall, the tics come out.
The movie itself doesn't make a lot of sense. Sexton Blake is enlisted to track down the head of the evil Black Quorum. He suspects Larron, a fellow stamp collector, and this suspicion is confirmed when he is captured after entering the Quorum's safe house. Larron sees him coming a mile away with his fancy closed circuit tv technology, but instead of killing Blake, the ties him up and attempts to burn the house down. Blake is rescued by femme fatale Julie, an intelligence agent on the same trail. Unfortunately, Larron has his eye on HER, too, and at the end of the film, he "collects" her and puts her in a death trap with Blake's sidekick, Tinker. Blake is obliged to rescue them both. The weird thing about all of this is that individual elements don't really lead to any other elements. There are a LOT of talking killer scenes in this movie, mainly built around Slaughter's persona. In fact, these scenes seem to be the entire reason the movie exists. Like any good master criminal, he escapes in the end, even though he never played the role again. You can see a blatant early example of franchise building in this movie, even though later Sexton Blake movies didn't take advantage.
There's a dated quaintness in this movie that makes it seem even more out of time than Slaughter's Victorian roles. This movie's version of superscience--closed circuit television--may have been cutting edge in 1938, but it seems like a ridiculous contrivance now in our surveillance society. And it seems out of place with its Indian blow darts and secret occult criminal cabals. What this seems like is an overdressed chapter play. Don't get me wrong, there's certainly pleasure to be had from this, particularly if you have a nostalgia for this kind of poverty row entertainment, but if it wasn't for Slaughter or for its ancestral relationship with James Bond (a bridge, if you will, between Holmes and Bond), I doubt anyone would watch this these days.
Oh, and for the record, my favorite Moriarty is Henry Daniell in The Woman in Green.