As a result of the dog fight with the flying monster, most of the plane's fuel is gone, leaving only a two- to three-hour supply. They must replenish the fuel somehow, since it is their only way to keep watch over the mountain pass at the far end of New Valley. Using an abandoned gorilla truck and a map Brent found inside, Bill and Jeff leave to find more fuel, planning to travel only at night and hide inside an old farm house. Meanwhile, Urko orders his troops to find some way of getting into New Valley to capture the humans. After Bill and Jeff have left in the truck, Nova becomes very ill. Thanks to Brent's 21st century medical training he diagnoses the symptoms as Acute Infectious Streptococholus, a very contagious lung disease which is fatal after seventy-two hours. Ron does remember that there is a serum that will cure the victim and immunize others. Judy suggests that Zira and Cornelius could help and takes the P-40 to meet up with Jeff and Bill at the farmhouse. Bill and Jeff are surprised to spot the aircraft overhead just as they reach the farm house. Judy lands the plane, which is now completely out of fuel, and explains Nova's situation to the men. They now have a deadline of a day and a night to get more fuel, obtain the serum and return in time for Judy to fly back to Nova and the tribe. Judy reaches the lab and Zira and Cornelius agree to make the serum. Meanwhile, the men have reached the abandoned air base on foot and begin loading fuel into the truck. Cornelius finishes the serum just as Dr. Zaius, seeing their light, enters to check on them. He leaves quickly after Cornelius lies to him that the serum is highly explosive, but there is not enough time left to deliver the serum back to Nova before she becomes contagious. So the Apes disguise Judy as a patient and drive her quickly back to the plane. Bill and Jeff have finished loading the fuel and are forced to risk using the highway in order to reach the farm house before sunrise. The truck overheats, so they head back to the river for water. Meanwhile, Zira and Cornelius are stopped by a gorilla road block. They tell the soldiers that their "patient" died of a very contagious disease, and are allowed to pass. Bill and Jeff get the water they need for the truck as it begins to storm, but are spotted by a gorilla patrol. They run for the truck as the gorillas cross the river by raft and they refill the radiator and get away. Judy and the chimps arrive at the farmhouse before the men and when the men finally arrive with the fuel, Judy takes off with it. She reaches New Valley in time to save Nova and prevent the disease from spreading.