Captain America: The Purple Death (1944) [colourised]

Captain America is a 1944 Republic black-and-white serial film loosely based on the Timely Comics (now Marvel Comics) character Captain America.

Like the Flash Gordon video, I've taken the decision to age-restrict this video too: while 'Cap is still a firm family favourite, 1944 Captain America is a different character entirely to the current MCU 'Cap. A little bit angrier.

This episode is public domain:
https://publicdomainmovies.info/captain-america-1944-serial-chapter-1-purple-death/

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Plot (Wikipedia) [⚠ spoilers]
https://en.wikipedia.org/wiki/Captain_America_%28serial%29

A rash of suspicious suicides among scientists and businessmen, all found holding a small scarab, gets the attention of Mayor Randolph. He demands that Police Commissioner Dryden and District Attorney Grant Gardner get to the bottom of the case, while openly wishing that Captain America, a masked man who has helped defeat crime in the past, were around to solve the mystery. Gail Richards, Grant Gardner's secretary, investigates and realizes someone knows of the "Purple Death", a hypnotic chemical responsible for the suicides. However he then pulls out a gun and takes her into another room. He then orders an associate to tie her up. The D.A. realizes she is there and forces the man to take him to her. He finds her tied up and gagged. He frees her but it is threatened that the purple death will be dropped killing them all. But the D.A. shoots him then gets out of the room with Gail.

All of the suicides were members of an expedition to some Mayan ruins. One of the few remaining survivors, Professor Lyman, turns to his friend Dr. Maldor for support. Dr. Maldor, however, reveals that he is the man responsible for the deaths. He wants revenge because he planned and organized the expedition but everyone else claimed the fame and fortune. However, Lyman has developed the "Dynamic Vibrator" - a device intended for mining operations but one that can be amplified into a devastating weapon. Using his purple death Dr. Maldor forces Lyman to disclose the location of his plans.

Captain America intervenes as the Scarab's heavies attempt to steal the plans and this leads to a sequence of plots by the Scarab to acquire a working version, as well as other devices, while trying to eliminate the interfering Captain before he succeeds in discovering Dr. Maldor's true identity or defeats him.