This 1951 film is a feature re-issue of the 1949 12-chapter Republic serial "King of the Rocket Men" edited down to 65 minutes, which basically means that players such as Tom Steele, David Sharpe and Eddie Parker who had as many as four-to-five different roles (in addition to stunt doubling) in the 12-chapter serial only pop up here in two-three different roles but spaced closer together. Both versions find the diabolical Dr. Vulcan (I. Stanford Jolley) causing the deaths of Professors Drake (Dale Van Sickle in one of his five roles in the serial version)and Millard (James Craven, chewing less scenery than usual for him) of Science Associates, a privately-operated desert research project. The "accidents" attract the attention of Glenda Thomas (Mae Clarke), photographer for Miracle Science magazine. She visits the project and is placated by publicity director Burt Winslow (House Peters, Jr.) and project member Jeff King (Tristram Coffin.) Later, Jeff visits a cave where he has been hiding Professor Millard, who wasn't killed but wants it thought he was, so he and Jeff can work on a rocket-propelled flying suit they have invented, with controls limited to "on", "off", "up" and "down" that work very well, thank you. Periodically, Jeff dons the suit and, as the mysterious Rocket Man (David Sharpe doubling for Tris Coffin), frustrates countless sinister plans (far fewer in the 65-minute version) of Dr. Vulcan to get control of Science Associates' devices which, if in the wrong hands, i.e, Dr. Vulcan, could easily wreak world-wide disaster. Vulcan finally gets his hands on Professor Millard's Decimator, capable of disintegrating rock strata, and plans to use it against New York City if the Mayor doesn't meet his billion dollar ransom demand. The Mayor isn't having any of that,and soon the city is rocked with an earthquake and tidal waves in the harbor, courtesy of stock footage from Republic's 1939 "S.O.S.Tidal Wave." Can the Rocket Man save the city?