After returning from a scouting mission in a time machine, the Mandroid hands a Roman centurion shield to Abbott Reeves [Roy Dotrice]. Reeves immediately orders the Mandroid to be dismantled, but his assistant Takada [Tad Horino] steps in, trying to help the captive escape. Although Takada sacrifices himself in the attempt, he leaves the Mandroid with a crucial lead: seek out scientist Nora Hunter [Denise Crosby] to help foil Reeves’s looming evil plan. In the United States, the Mandroid finds Nora and reveals his true nature. Nora, who had believed Reeves was dead, recognizes the Mandroid’s new Mars-probe design and begins repairing the damage done to him. As she renovates the machine, the Mandroid makes clear his intent to return and put an end to Reeves’s schemes, whatever they may be. To help him, Nora joins as his mechanic, bringing along S.P.O.T., her own compact flying scout robot.
Their adventure continues as they reach Mexico, where Nora secures a guide in the roughest of bars: Harry Fontana [Andrew Prine], a riverboat captain with a taste for trouble. Fontana becomes their rough-edged ally as they float down a winding river, navigating clashes with rival riverboat chiefs and Reeves’s men. The journey leads them to the Mandroid’s crashed plane, a find that occurs after a tense confrontation with a tribe of cavemen—brought forward in Reeves’s time-travel experiments. In the midst of the frontier, they also encounter Kuji [Conan Lee], a ninja warrior and the son of Doctor Takada, who has come in search of his father. The Mandroid informs Kuji that Takada is no longer alive, killed by Reeves, and Kuji makes the choice to join them on their mission.
With Kuji aboard, the group breaches Reeves’s headquarters, only to be captured by Reeves himself, a cyborg far more advanced than the Mandroid. Reeves’s plan unfolds: he intends to slip back to ancient Rome and seize control as a modern Caesar. In the ensuing showdown, the Mandroid fights valiantly but is overwhelmed and badly damaged. In a final act of sacrifice, the Mandroid frees his companions, allowing them to pursue Reeves to his laboratory. They witness Reeves escape into his time machine and blast off toward ancient Rome, leaving Fontana to an act of necessity: he crashes the lab’s control panel, causing the machine to overshoot its target date and fling Reeves hundreds of millions of years into the past.
In the end, what began as a clash of technology and time becomes a race against a tyrant who seeks to rewrite history. The Mandroid’s sacrifice, the stubborn bravery of Nora Hunter, the loyal grit of Fontana, and the unexpected aid of Kuji converge as a last stand against a future dictated by Reeves’s chrome-plated ambition. The result is a bold blend of sci-fi adventure and pulp-style heroism, where science and courage collide across the ages, and where a single act of defiance can alter the trajectory of time itself.
