FRYEAN MYTHOS: *adventure*
CAMPBELLIAN FUNCTION: *sociological*
PURPLE MONSTER-- which is what the Martian villain pictured above (Roy Barcroft) calls himself, sans any explanation-- is credited with being the first postwar serial based in science fiction tropes. He's just as much of a one-dimension "foreign invader" as many of these seen prior to and during WWII, but it's interesting that Republic Studios does a nice job of blending sci-fi "gadget-philia" with the thrills and spills of action-cinema-- something one doesn't see in the last two FLASH GORDON serials from Universal. I can imagine PURPLE MONSTER being very influential on Sam Katzman's Columbia serials, some of which share the heavy emphasis on gadgets but aren't nearly as good devising adventure[-scenarios.
In a twist on the familiar theme of world conquerors trying to latch onto new devices created by peace-loving American scientists, the Purple Monster, a native of Mars, arrives on Earth in a spaceship, and he's come looking for Doctor Layton. Layton has plans for devising a new type of jet-plane for peaceful interstellar exploration, but the Monster wants to create the vehicle so that he can take it back to Mars so that his people can create an invasion fleet.
The Monster then introduces his most prominent gadget: a vial of "Martian gas." He exposes Layton to the gas, which is immediately fatal to the Earthman. However, when the Monster exposes himself to the gas, it has a very different effect, which the script never attempts to explain. The gas causes the Martian to become invisible and insubstantial-- making him akin to a spirit. In this form he possesses and revives Layton's body, now entirely inhabited by the Martian's intelligence. For the remainder of the series, the false Layton-- much like the "false father" seen in 1941's JUNGLE GIRL-- orders various thugs to work his will. Neither of the two heroes-- Layton's niece Shelia and his two-fisted attorney Craig Foster-- realize until the serial's end how they've been manipulated and endangered by the phony scientist.
Many chapters are fairly repetitive "chase-down-the-next-part-we-need" schticks, though the fight-scenes are top of the line for Republic Studios. Late in the serial the one-man invasion force appeals to get an aide, a Martian female with the un-ironic name "Marcia." Marcia kills off an Earthwoman to assume her identity and has a tussle with Shelia (Linda Stirling) in one chapter, but this time heroine Stirling doesn't even get as much action as she did in the same year's earlier MANHUNT ON MYSTERY ISLAND. Craig (Dennis Moore) gets to have all the fun, including dealing the death-blow to the evil invader.