On the bridge of an alien spacecraft, the servants of the Galaxy Master dispatch the titan time-probe to determine the identity of the one responsible for the defeat of Umbu.
Ka-Zar emerges from a cave carrying the lifeless body of Bruce Banner. Sensing that life may yet be preserved, Ka-Zar and Zabu enter the jungle to find rare herbs in order to revive Banner. The alien probe finds the now defenceless body, and Ka-Zar returns to discover Banner is missing.
Following the tracks of Banner’s abductor, Ka-Zar reaches the outside world, but the trail mysteriously ends. The aliens have found someone who had the power to smash Umbu, but their puzzlement arises when they are presented with a dead human.
They place Banner within a resuscitator so that they can revive him and question him. The scanning of his mind reveals that Banner is one of Earth’s most brilliant scientists who discovered the doomsday machine and shut it down.
(Note: The alien mind scan does not reveal Banner’s true identity because he has no memories of being the Hulk).
The crew of the vessel argues over the fate of the human when suddenly the Galaxy Master appears and declares the one who thwarted his plans must perish.
They lead Banner to a decompression chamber, where he transforms into the Hulk and smashes a hole in the ship's side.
As the Hulk finds himself in space, he reaches out and grabs onto the ship, defending himself from the lasers that are firing at him.
The aliens launch attack spheres to deal with the ‘intruder’ and the Hulk battles in space, easily defeating the soldiers.
After achieving another victory against the aliens, the Hulk goes on the offensive, climbing into the exhaust port. The commander orders the rocket to be fired, hoping to hurl the Hulk into space. But the Hulk finds a handhold and fights the heat and pressure to make his way to the engine.
When the engine gets destroyed, the ship must land on its home planet. During the landing, the commander orders his crew to crush the Hulk under the ship. But Hulk leaps aside at the last moment. Now that he is on the ground, Hulk will make his attackers pay. However, before he can carry out a counterattack, the Galaxy Master appears and tells the Hulk not all his strength will keep him from being destroyed!