Bill, Jeff, and Judy are heading for the humanoid settlement across the plain between the mountain ranges when they spot what look like humans far below. Bill calls to them, but Jeff quickly stops him -- the figures are dummy targets. Suddenly, to their amazement, a World War II-era Curtiss P-40 fighter plane appears in the sky. Piloted by a gorilla, the aircraft flies toward the dummies and drops a net on them. Apparently, the Ape army is testing the plane in preparation for war games. Bill concludes that with the plane, there will be no stopping Urko from capturing every human and that they must try to steal it. Later at the ape plane hangar, Urko congratulates Dr. Likis, the ape scientist who restored the flying machine, and wants the aircraft ready for an air demonstration for Dr. Zaius the following day. He then visits Zaius, and demands that Zaius give him complete authority. He backs up his demands with threats of using the plane to secure his power. Zaius, fearing human technology from the past, wants Urko to destroy the plane.
Zira and Cornelius receive an invitation at their lab for a demonstration of a new "secret weapon". They see a flash and realize it is Bill signaling them. They all meet in the clearing where Bill tells the apes of Urko's aircraft and their plans to steal it. Cornelius gives them directions to Urko's fortress. Reaching it, the three cause a diversion with some barrels that lets them slip past the guards and find the plane's hangar. They discover that, using the old P-40 fighter as a guide, the apes are building an entire fleet. To make matters worse, humanoids are being herded as target practice in the next day's demonstration. Back at the lab, Cornelius is concerned that Urko, with his hunger for power, might resort to using his air force against apes to gain control of the government. Inside the hangar, Judy thinks that she could fly the P-40 away during the airshow as the plane might be very useful to the humans. The next day all of Ape City has turned out to see the demonstration. Jeff and Bill secretly pose as messengers bringing a good luck gift to Largo, the ape who is to fly in the airshow, and tie him up. As wagons of humans are trucked onto the field, Judy disguises herself in Largo's flight suit and is escorted there as well. Largo, who has managed to free himself, tries to warn Urko by radio, but Jeff and Bill had cut his radio wires. When Largo enters the field, Urko realizes that someone else is flying. At that moment, Jeff and Bill send a locomotive crashing into the aircraft factory, destroying it. Dr. Likis tells Urko that without the original plane, no further aerial research can be done.
Bill and Jeff manage to round all the humans into the truck and speed off with soldiers pursuing while Judy drops the net meant for the humans on the apes and they crash. Zaius ends the disastrous demonstration by recommending an investigation into Urko's command abilities be conducted at once. Zaius later decide that Blue Eyes must have been responsible for the day's events and warns Cornelius and Zira (despite their claims that they had nothing to do with it) of the danger in aiding fugitives. Judy lands the plane in the desert and they wonder if it could ever help them get back home.