and Kolos, touched by her warmth towards him, allows her to remain an original being. He does not believe that the helpless young girl can become a threat to the success of his diabolical mission.
The National Intelligence Agency, headed by Austin Welles (Hugh Beaumont) is baffled by a series of mysterious robberies occurring at important research facilities. In each case the prime suspect is a leading scientist and staff member of the robbed organization. In each case the suspect has vanished without a trace.
After careful investigation, special agent, Glenn Martin (George Nader), with the assistance of undercover girl, Gale Wilson (Barbara Nichols), deduces that the highly respected Professor Dornheimer is the mastermind of the intrigue. But in order to prove his deductions, Martin must gain access to the well guarded mansion.
In the mountains near the Dornheimer estate Martin discovers an abandoned mine, and a tunnel which leads him to a secret entrance into one of several basements of the mansion. A chamber of horrors awaits Martin's investigation. In one stone room, a refrigeration vault, he finds the frozen bodies of the missing robbery suspects and numerous other persons. In another chamber Martin finds synthetic components of the human anatomy, male and female - legs, arms, torsos, and heads. Then finally, Glenn Martin finds his way into the electronics lab where he witnesses a monstrous operation. He watches from the shadows as a beautiful Chinese girl, a noted chemist, is duplicated by the professor and his assistants.
But Glenn Martin's observations are brought to a sudden halt. He is caught by Kolos, then he too is duplicated, and the brain of his twin is programmed for a special assignment. The real Glenn Martin is held prisoner in the mansion while the duplicate returns to the National Intelligence Agency with false information regarding professor Dornheimer. Then, satisfied that neither Austin Wells nor Gale Wilson are suspicious, the android Martin proceeds with his assignment, the theft of a government electronics supply vault.
But undercover agent, Gale Wilson, has become suspicious, and as a result she and Welles catch the duplicate Martin in the act. Martin escapes in the night, speeding towards the Dornheimer estate with the police in hot pursuit.
In the meantime, Dornheimer's niece, Lisa, has come to the real Martin's aid. She has helped him escape from his cell in the lower basement of the mansion, and with the aid of the real professor, who has also been held a prisoner, Glenn Martin brings about the destruction of the androids. By concentrating a laser beam on the heads of the robots, Martin causes a mental breakdown in their delicate brain mechanism. The mechanical men begin fighting themselves. It is a vicious struggle to the end.
As Gale Wilson, Welles, the real Martin, and an astonished group of police look on, the cosmic agent, Kolos, informs them that he will leave planet earth and return to the galaxy beings with his report of failure. He has failed, not because he is weak, but because humans are stronger, because the beings of earth have a basic element the galaxy masters do not possess. The human being has faith in each other, they have a heart. Kolos then announces that on his return to his superiors he will be destroyed, but it will not matter, for he knows now what he hadn't known when he arrived he too is an Android.