The Mysterious Mr. M (1946)

Anthony Waldron, who supposedly died in Africa, returns with the formula for a drug called "hypnotrine" that can make anyone do his bidding. Using an alias of "Mysterious Dr. M", he plots to steal a revolutionary engine design from Dr. Kittridge that will permit ocean liner-sized submarines to reach a speed of 30 knots underwater. He is hiding in a basement laboratory that is accessed via a button in a desk drawer that activates a hidden entrance behind a fireplace. Kittridge farmed out various components of the engine to other manufacturers, often using false names. Three parties are all after acquiring them - the U.S. government, Waldron and an unknown third party who has appropriated the Mysterious Mr. M tag. Federal agent Grant Farrell is sent from Washington, D.C. to Mid City to end Waldron's pursuit of engine sub-assemblies. Homicide Chief Dan Blair, detective Kirby Walsh, and insurance investigator Shirley Clinton join Farrell. Periodically, Anthony Waldron must obey the other Mysterious Mr. M. Farrell is puzzled by how information leaks about components get into the wrong hands just before he can track them down. Part of the time the leak is Kirby who was dosed with hypnotrine. The second Mr. M communicates his requests to Waldron via records that show up unexpectedly all around his house and lab.