Bruce Banner has created an indestructible robot that will allow its passenger to study atomic bomb blasts from a short distance. Thunderbolt Ross is impatiently waiting for Banner. His daughter Betty Ross tries calming him down. Banner arrives late at the Air Force base because he was trapped in his cave as the Hulk.
While double checking his robot plans, Banner realizes he changes into Hulk (and back) during extreme moments of stress. Banner theorizes that if he avoids any strain, he won’t change into the Hulk.
Thunderbolt Ross tells Banner that they have scheduled the robot test for the next morning. Banner works all night to finish his creation. He hears someone on the premises and when he chases him, strain turns him into the Hulk, who leaps away into the hills.
The unknown man, a spy, knocks out a soldier watching over the lab and enters the robot to walk into the testing area.
Ross and his men learn about the attacked soldier, believe Banner did it (!), and dispatch a remote controlled tank to stop the robot. But the robot withstands the shells and breaks the tank with a blow. The spy now dreams of selling the robot to foreign countries to make a fortune, or conquer the world with it.
Hulk sees the robot, believes Banner has created it to defeat him and attacks. But his fists prove useless against the indestructible machine.
The strain of fighting something stronger than himself (for the very first time) makes Hulk turn into Banner (!).
When soldiers find Banner, he explains Ross and Betty that someone else is inside the robot. Ross is furious. Betty tries comforting his loved one. But Banner feels horrible because he has endangered humankind a second time by creating another terrible menace which is like or worse than the Hulk.
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