Phantom Creeps Chapter 10: Phantom Footprints

The Phantom Creeps is a 1939 serial starring Bela Lugosi as a mad scientist who attempts to rule the world by creating various elaborate inventions. In a dramatic fashion, foreign agents and G-Men try to seize the inventions for themselves. Also starring Dorothy Arnold and Robert Kent.

Dr. Zorka, a rogue scientist, is the creator of various weapons of warfare, including a devisualizer belt which renders him invisible; an eight-foot tall slave robot, robot spiders that can destroy life or paralyse it and he also has a deadly meteorite fragment from which he extracts an element which can induce suspended animation in an entire army. Foreign spies, operating under the guise of a foreign language school, are trying to buy or mostly steal the meteorite element, while his former partner, Dr. Fred Mallory, miffed that Zorka will not turn his inventions over to the U.S. Government, blows the whistle on him to Captain Bob West of the Military Intelligence Department. Tired of answering the door and saying no to the spies and the government, Zorka moves his lab. When his beloved wife is killed, Zorka, puttering around for his own amusement up to this point, is crushed and swears eternal vengeance against anyone trying to use his creations and to make himself world dictator. And would have if not for his assistant Monk, an escaped convict virtually enslaved by Zorka, who is cowardly, treacherous and totally incompetent, and whose accidental or deliberate interference with Zorka's efforts repeatedly frustrates his master's own plans...

text from wikipedia