Captain America is a 1944 Republic black-and-white serial film loosely based on the Timely Comics (today known as Marvel Comics) character Captain America. It was the last Republic serial made about a superhero. It also has the distinction of being the most expensive serial that Republic ever made. It also stands as the first theatrical release connected to a Marvel character; the next theatrical release featuring a Marvel hero would not occur for more than 40 years.
The serial sees Captain America, really District Attorney Grant Gardner, trying to thwart the plans of The Scarab, really museum curator Dr. Cyrus Maldor - especially regarding his attempts to acquire the "Dynamic Vibrator" and "Electronic Firebolt", devices that could be used as super-weapons.
In a rare plot element for Republic, the secret identity of the villain is known to the audience from the beginning, if not to the characters in the serial. The studio's usual approach was the use of a mystery villain who was only unmasked as one of the other supporting characters in the final chapter
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 investigates and realises someone knows of the purple death. 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. realises 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 organised 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", a hypnotic chemical responsible for the suicides, 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.