Undersea Kingdom

Following a suspicious earthquake, and detecting a series of signals, Professor Norton leads an expedition, including Lt. Crash Corrigan and reporter Diana Compton, in his rocket submarine to the suspected location of Atlantis. Finding the lost continent, they become embroiled in an Atlantean civil war between Sharad (with his White Robes) and the usurper Unga Khan (with his Black Robes). Khan wishes to conquer Atlantis and then destroy the upper world with earthquakes generated by his Disintegrator. Thus, he will rule the world unless he can be stopped in time. The star of the serial is Ray "Crash" Corrigan, using that screen name for the first time. The name was created to sound similar to "Flash Gordon", in one of many similarities. Formerly a stunt man – he was the person swinging on vines in Tarzan the Ape Man (1932) – Corrigan went on to use this screen name for the rest of his career in serials and B Westerns. The first two chapters of the serial were mocked on the TV show Mystery Science Theater 3000 in July/August 1992.

The plot involves the main character "Crash" Corrigan trying to stop an evil tyrant ruler of Atlantis from conquering the lost continent and then the entire upper world. Lieutenant Crash Corrigan, in his last year at the United States Naval Academy in Annapolis, Maryland, is invited by Billy Norton to visit his father, Professor Norton, after a wrestling match. At their house, the professor is demonstrating his new invention, which can detect and prevent (at short range) earthquakes, to Diana Compton and his theory about regular tremours from the area where Atlantis used to be. When Atlantean tyrant Unga Khan and his Black Robe army turn their Disintegrator beam on St Clair, Professor Norton leads an expedition to investigate. Along with him in his Rocket Submarine are Crash, Diana, three sailors (Briny Deep, Salty, Joe) and their pet parrot Sinbad. Unknown to the expedition until it is underway and in trouble, Billy has stowed away on the Rocket Sub as well. Problems for the expedition begin when Joe, in charge of the engine room, is driven mad by the fear that the submarine cannot survive such depths. In order to prove this, he locks the engine room door and sends the sub into a fatal dive. As soon as this crisis is averted, Unga Khan and Captain Hakur detect their approach and bring them through a tunnel into the Inland Sea with a Magnetic Ray.

While the technology base of Atlantis is apparently very low, with sword wielding cavalry and chariots the main type of military force, Unga Khan's Black Robes (or Imperial Guard) have several very advanced items of technology. Unga Khan's Disintegrator is the main plot device. A machine capable of artificially creating earthquakes at a precise target, it is this that leads to Professor Norton's expedition to Atlantis and also the means by which Unga Khan means to conquer or destroy the upper world. The Reflector Plate is the most ubiquitous device used throughout the serial. This is a screen that acts much like a view screen, or videophone, in more modern science fiction. It is used to communicate between two plates or it is used, most frequently, to view (and hear) any remote location. No cameras or microphones are apparently necessary to this second function and it appears to have no limits viewing the Sacred City, areas of Atlantis and the upper world with no problems. Unga Khan's Imperial Guard are augmented by Volkites, a type of robot controlled by a bulky remote control device often worn by Hakur. They also perform tasks in the tower, for example operating the Master Controls of other devices such as the Disintegrator when commanded to by remote control (the remote control of most devices is usually done through remotely controlling the Volkite(s) to operate the Master Controls to remotely control the actual device). While the Imperial Guard use swords or bows, the Volkites are armed with Atomguns, rifle sized ray guns. Occasionally these are used by others where necessary but only when taken from a Volkite. In terms of vehicles, Unga Khan has one tank, called the Juggernaut. This can be controlled by remote as well as by the driver (either human or Volkite). It has no armament itself but is used as a battering ram during siege warfare. Though not used very often, Unga Khan's forces also have several aircraft called Vol Planes (also known as Sky Chariots by the White Robes). Unga Khan's tower is armed with one Projector which fires one Aerial Torpedo at a time. This is, again, controlled by remote control. Unga Khan uses his Transformation Chamber to brainwash those unwilling to do his bidding. The effect wears off in time and can be reversed by the Chamber. The Magnetic Ray is used only once to pull the Rocket Submarine into Atlantis (much like a tractor beam in Star Wars or Star Trek) in the first chapter. In the last chapter, an Invisible Wall of Atom Rays is activated to provide Unga Khan's tower with a force field to protect it from the United States Navy's bombardment. Finally, the tower itself has automatic sliding doors and elevators. The most advanced technology seemingly available to the opposing White Robes of Sharad are catapults and flame throwers built into the walls of the Sacred City.