While vacationing on Norway, American Dr. Donald Blake is witness of an alien invasion by Stone Men from Saturn. Discovered by the aliens, Blake hides in a cave where he accidentally opens a secret door that leads to a chamber that holds an ancient wooden cane. Blake tries using the cane to move the boulder out of the cave's exit but is unsuccessful. Striking the rock in anger, Blake transforms into a tall, muscular being of immense strength and the cane into a large hammer with an inscription that says "Whosoever holds this hammer, if he be worthy, shall possess the power of... Thor"
Blake realizes that he's turned into the "mightiest warrior of all mythology" and easily escapes the cave. Blake then quickly learns that he reverts back to his human form if he leaves the hammer for more than a minute. He also learns how to cause storms with the hammer, and that it returns to him automatically after throwing it against a target.
Meanwhile, the Stone Men have launched the invasion on Earth and human opposition (NATO Armed Forces) are worthless. Blake as Thor, hurls the hammer to lift himself upon the air, finds the invaders and defeats them including their Mechano-Monster. The Stone Men flee, Thor turns back into Blake and the NATO men are clueless as to why the terrible menace has ended.