MacGyver flies in by helicopter toward a satellite reentry zone while Pete monitors him from a defense communications facility. Nine hundred sheep are dead on the ground at a sheep ranch and MacGyver feeds the image to Pete by camera. Pete assures the military man, Phelps, that MacGyver is the man for the job and knew what he was getting into. The news has picked up on the dead sheep from local farmers and Pete wonders if the person responsible, Dr. Sandra Millhouse, is watching. An organism sent into outer space on a satellite mutated and crashed, and MacGyver is there to recover the satellite before the military launches a napalm strike to cleanse the area. He has 42 minutes to recover the satellite before the military strikes. MacGyver finds other dead animals and the military start flying over. MacGyver demands that Phelps draw them back and Pete backs him. Phelps reluctantly gives the order and MacGyver continues on toward the satellite crash zone. He finds the satellite but then slips down a slope. The camera goes out and MacGyver is knocked unconscious.
Phelps assumes that the virus in the satellite killed MacGyver but Pete insists he's okay. MacGyver recovers consciousness but his radio antenna is out: he can hear them but can't talk back. Pete wants to give him the time agreed upon but Phelps notes they knew what they had to do. He calls in the jets to launch napalm and Pete gets on the radio to tell MacGyver what's going on. MacGyver gets to the satellite with the jets 40 seconds out. MacGyver uses the radio dish from the satellite to boost his camera image and they get the signal just in time: Phelps calls the jet off. MacGyver recovers the sample from the satellite and puts it in a containment unit, then signals for pickup.
Pete takes Phelps to a Phoenix Foundation facility with the main laboratory six stories underground. Most of the staff have been given the weekend off and only essential personnel are present. They descend to Millhouse's laboratory and Pete looks for Millhouse. He finds her puppy Ace in the hydroponics lab and finally locates her in a separate area. He isn't happy that Millhouse snuck the sample on to the Phoenix Satellite without permission, and warns she hasn't learned anything since the last time she tried something similar. Millhouse is impatient with the bureaucrats and tells him not to push the panic button too soon. She insists the information she acquired is vital and they need to see it through, but Pete tells her it's over. Phelps arrives to tell them MacGyver's on his way. He arrives and sends the sample down separately, then goes down to Level Six for decontamination. Phelps is leaving to deal with the ranch they burned down and apologizes to MacGyver, who insists it isn't necessary.
Millhouse is examining the mutated sample and Pete warns it's dangerous. MacGyver arrives and notes that it's killed. Millhouse brings in a white rat but MacGyver objects. She relents and MacGyver confirms there was a crack in the canister. Millhouse analyzes the mutated sample and determines it's getting stronger. Phelps brings in the autopsy report which shows that all of the animals died of physiological symptoms consistent with old age. Millhouse insists that the sample can be used to accelerate plant growth but Pete insists on telling the government the truth. He leaves with Phelps and Millhouse shows MacGyver her hydroponics lab which contain trees that are immune to extreme environments and pollution. She insists she wants to solve world hunger and isn't concerned about the right way and the wrong way: she just wants results. Pete comes in and informs her that the government has given orders to destroy the organism. Millhouse refuses but is interrupted when the alarm goes off informing them the lab integrity is compromised. They go to the lab and spot the seal starting to dissolve. MacGyver determines that the sample has mutated and is eating through the sealing compound. The destruct sequence will activate in seven minutes if integrity isn't restored.
MacGyver improvises a seal by using a Bunsen burner to heat up the material, then freezes it once it's filled in the holes. The seal holds but MacGyver warns the sample could start eating through glass. Millhouse reluctantly activates the laser in the containment chamber and destroys the sample. She puts a white rat in the chamber to confirm the organism is dead. Phelps leaves to inform Washington and Millhouse tells Pete and MacGyver to get the hell out. As they leave, MacGyver goes back to talk to Millhouse and notes that while he is big on experimentation, it's too risky. Millhouse shows him the computer disk with the data she's accumulated over the years. MacGyver assures her that it might take longer, but she'll eventually develop her solution.
Up above, Pete and MacGyver say goodbye to Phelps and Pete admits he's going to file a poor recommendation against Millhouse. However, Pete talks about the time she smuggled a virus out of a laboratory in a dog's bladder. He figures she won't give up... and they both realize she gave up way too easily. They head back to the lab. Below, Millhouse goes to the hydroponics lab with her dog and removes an extra sample that she set aside. MacGyver arrives and she seals the greenhouse, and explains she set the sample aside anticipating someone would order her to destroy it. She insists nothing will happen... and Ace leaps up and knocks the sample out of her hand. It smashes on the floor and MacGyver looks on in horror. Millhouse calls Ace over but he's already started to age. The integrity alarms go off and an aging Millhouse cradles her dog while admitting to MacGyver that he was right. MacGyver runs to get a protective suit and Pete looks on as the now horrendously-aged Sandra lies dying. She thanks them for trying and notes the contagion has mutated to age plant life as well. The alarm informs them the self-destruct will activate in seven minutes and Millhouse asks Pete to save her work. MacGyver goes to get the diskettes and returns to tell Sandra they got the information and will get it out. She whispers out a "thank you" and dies.
With five minutes remaining, the section doors close and the two men get out ahead of the doors. They get to the elevator and pry the doors open. However, the elevator has shut down. MacGyver boosts Pete up to the roof of the car and follows him up. However, the maintenance override switch only raises the car a few inches at a time. Pete opens the door and MacGyver goes to the laboratory and removes the transformer. He hooks it up to the manual override switch and boosts the power and they start to ascend up the shaft. They get to the top with no time to spare and run out of the upper level as fire blasts through the laboratory and up the shaft. They can only mourn the loss of life as they walk away.