A tyrant from Atlantis plots to conquer the upper world with robots, death rays, etc. Our Hero continuously thwarts the bad guy after he discovers Atlantis while riding in his rocket-powered submarine.

Newspaper reporter Diana Compton and Navy lieutenant Crash Corrigan learn from Prof. Norton that a series of destructive earthqueakes originate from the submerged kingdom of Atlantis on the ocean floor. Boarding his futuristic roccket submarine, Prof. Norton journeys beneath the sea to Atlantis with Diana, Crash, Norton's young son Billy and three sailors, Joe, salty and Briny. Joe pancking as the rocket sub dives far below the waves, attempts to scuttle the expedition, but Crash prevents this disaster.

Ten thousand feet eblow the ocean's surface the explorers emerge in lost Atlantis, which is protected from the waers above by ahuge dome that encloses the fabled land. They discover that Atlantis is in a state of perpetual civil war as two politcal factions (one ruled by relativly beevolent monarch Shard, the other controlled by the cruel tyrant Unga Khan) battle for supremacy. When the explorers are accosted by Unga Khans men, Joe panics and is killed by Volkite robots using ray guns. Crash and Billy manage to escape, but Diana and Norton are captured and taken before Unga Khan. In his scientifically advanced headquarters, located in a metal tower, Unga Hjan reveals that he plans to raise the tower above the waves using rocket engines for propulsion, and the conquer the surface world. The ruthless tyrant mesmerizes Prof. Norton, dominating his mind and forcing him to work toward this end.

Meanwhile, Crash has been taken prisoner by sharad's forces. Sharad, believing that Crash is a Khan agent, sentences him to death in the combat arena. Crash emerges victorious, but refuses to kill his opponent. When Sharad is kidnapped by two of Khan's men who speed away with him in a chariot, Crash pursues and overtakes them, rescuing the monarch. A grateful Sharad rewards Crash by making him commander of the army.

Prof. Norton, his mind under Khan's control, continues to assist the tyrant in constructing rocket motors that will propel Khan's tower to the ocean surface. After several narrow escapes in their struggle against Unga Khan, Crash enters the tower headquearters and manages to rescue his friends and restore Norton's memory. But Norton has comepleted his work on the rocket engines; Khan ignites the engines, lifting the tower through the protective dome covering Atlantis. The sea rushes in, drowning the remaining inhabitants, but Crash's friends escape in the rocket sub, following the tower to the surface.

Remaining in the tower, Crash broadcasts a warning to the United States Navy that the tower is rising to the surface and poses a threat to humanity. Crash then escapes to the rocket sub with Prof. Norton, rejoining Diana, Billy and his other friends just before a US Navy Battleship blasts Unga Khan and his tower into oblivion.