On a plateau high above the Amazon river in South America, an ape army stands in formation before two evil men: Colonel Vaster and Dr. Rukas, who controls the apes using sonic vibrations from his backpack.
Experiencing engine problems, Clark lands the plane he and Lois are in at the nearby river. Clark goes looking for a boat and changes into Superman. Hearing an odd sonic voice, Superman ventures to a nearby town and apes attacking it run away in fear.
Learning of the ape army, Superman flies back to where Lois is and drives the apes there away. Superman brings Lois to her destination of an excavation site but it is deserted with a message scrawled on a wall stating that the apes are on the march. Superman gets Lois to stay at the site while he goes to look for Clark.
Vaster and Rukas learn from the apes that the archeologists have fled and look to get the gold buried at the excavation site. Vaster attempts to double cross Rukas but Rukas has an ape chase the rogue colonel and shove him off the cliff. Superman saves Vaster from certain death and learns the secret of the ape army.
At the excavation site, Rukas has an ape tie up Lois and looks for the gold. Superman arrives and saves Lois and ends Rukas' control over the apes, who quickly disperse.
Superman delivers Vaster and Rukas to the local authorities and afterwards, Clark says he went missing as he figured there was monkey business going on.