Part 1: The Coming of the Hulk
At an Army base in the desert, Doctor Bruce Banner is readying the first test of his invention, the G-Bomb. General "Thunderbolt" Ross wants to know why Banner keeps delaying the test. His daughter Betty tries to calm him down, with little success. Banner tells Ross that the final countdown has begun. His assistant, Igor, demands that Banner share his work so that someone may check his calculations. "I don't make errors, Igor," says Bruce, and, when Igor threatens him, "You know how I detest men who think with their fists."
Banner takes a last look at the bomb with binoculars. He notices a teenage boy in a car, tells Igor to halt the countdown, and hurries after the boy in a jeep. Igor, who supposedly defected to the U.S. from the Soviet Union, is a spy and decides not to stop the countdown so that America will lose its greatest nuclear physicist. Banner gets the boy into a trench, but, before he can jump in himself, the G-Bomb explodes! Gamma rays saturate Banner's body.
Hours later, Banner regains his senses. The boy, Rick Jones, who drove onto the base on a dare, brought him back to base. Banner waits for some kind of symptoms to appear. When night falls, Jones turns on a "radio," actually a Geiger counter. Its clicking increases, and Banner changes into a huge grey figure. "Get out of my way, insect," says the figure, shoving Jones aside. He pushes through the wall, wrecks a jeep full of soldiers when it hits him, and wanders off to hide. Jones follows.
Part 2: The Hulk Strikes!
The thing that was once Banner, with Jones trailing him, sneaks past the soldiers trying to find him and finds Banner's cabin. Inside, Igor is trying to find Banner's notes. He shoots at the Hulk, without effect. The Hulk takes away his gun and crumples it with one hand. He picks up Igor and slams him down on a lab bench. Jones notices a folder taped to the bottom of a large beaker, labeled "Top Secret: Report on Gamma Ray Bomb," and takes it. The Hulk picks up a photo of Banner and says, "I—I know that face!! But it is weak—soft!! I hate it! Take it away!" Jones reminds him that he is Banner. The Hulk briefly remembers what happened, then says, "I don't need you! I don't need anybody! With my strength—my power—the world is mine! As for you—you are the only one who knows who I really am!" He advances on Jones. The sun comes up at that moment, and the Hulk changes back into Banner.
Part 3: The Search for the Hulk
The MPs storm in, arrest Igor, ask Banner about the Hulk, take the folder, and leave. Betty comes to apologize for her father's outburst and tells him he should get medical attention. Banner says he'll call her and shows her out. He tells Jones that he's afraid he will change again at sunset.
Part 4: Enter ... the Gargoyle!
In his cell, Igor uses a transmitter overlaid on his thumbnail. The message finds its way to the Gargoyle, a deformed Soviet scientist and secret agent, who travels by submarine and short-range missile to the desert. Banner and Jones take a jeep out into the desert before night falls, in case he changes again. He does change, and the Hulk wrecks the jeep. He recognizes the area near Ross's house and decides to visit Betty. At the same time, Betty decides to take a walk. She encounters the Hulk and faints in his arms. The Gargoyle appears.
Part 5: The Hulk Triumphant!
The Gargoyle shoots the Hulk and Jones with drug-filled bullets, making them like robots. They follow him to a truck, whose driver also gets shot. Ross finds Betty, who was frightened by her encounter but says, "In spite of everything, there was something ... something sad about him!! Almost as though he was seeking ... help!" Ross says, "If it takes an eternity, I'll find that monster!"
The Gargoyle and his captives reach a sub on the coast and get into a jet. As they streak towards the USSR, the sun rises on the Hulk, who changes back into Banner.