MacGyver is driving through the California harvest town of Kasabian when his car breaks down. As he drives to a garage, a policeman warns him that the road ahead is blocked off. A worker and organizer, Tony Garcia, is addressing the crowd about how the contractors are poisoning them with illegal pesticides. The primary farm owner, Caspar Kasabian, steps forward to defend his record, insisting he follows the government regulations. Tony points out that the government has only a few inspectors to enforce the law and the owners often pay them off. At the back of the crowd, Caspar's son Nick is complaining to labor contractor Felix Mendoza that he's tempted to do violent about the workers but his father has ordered him not to start anything. When Tony and Caspar almost come to blows, a fight breaks out and MacGyver helps the workers against Kasabian's people and the police arrest all of them.
As MacGyver and Tony wait to be released with the other workers, Kasabian pays the bail for his men. One of them, Victor Lopez, is a former worker and a young worker, Alex Silva, accuses him of selling out. Tony tells Lopez to do what he has to, informing Alex that Lopez isn't the problem. Tony chats with MacGyver, thanking him for his help. He explains that the town of Kasabian has a high number of cancer clusters similar to those in other towns where pesticide use takes place. MacGyver points out that the government studies don't show the contamination but Tony wants to get recognition of their concerns from the farm owners.
The police arrest the workers that night and the sheriff talks to Tony privately. He warns Tony not to make trouble and insists that Caspar is doing what he can for the workers. Tony offers MacGyver the hospitality of his home until MacGyver can get his car fixed the next morning. As they drive, Tony claims that he has new information that should force Caspar to listen to him. A truck pulls up behind them and tries to drive them off the road while a passenger opens fire with a shotgun. Tony's truck goes off the road and he and MacGyver run toward the nearby trees. Tony runs off to draw their attackers and MacGyver hears a gunshot. When MacGyver goes to investigate, someone knocks him over the head and leaves him lying beneath an owl-shaped balloon. A few minutes later, a spray truck passes by, spraying MacGyver with pesticides.
The next morning, MacGyver wakes up at Tony's house. Tony's wife Carmen and his crippled daughter Natalie are looking after him. Alex is there and explains that workers found MacGyver in the fields and brought him to Tony's house. Tony has gone missing and MacGyver and Alex meet with the sheriff. The police have found Tony's truck but because a shotgun was used, there's no evidence to confirm the shooting. Alex accuses the sheriff of covering up the whole thing but the sheriff accuses MacGyver of being a labor organizer in town to stir things up. He orders MacGyver out of town but MacGyver refuses to leave.
Alex and MacGyver, showing symptoms of pesticide poisoning, go to the fields and find where MacGyver was knocked out. They notice a button on the ground and conclude it belonged to one of the attackers. MacGyver finds blood on a support post and they realize that Tony is certainly dead. They tell Carmen the news and MacGyver asks her about the new information Tony had. Carmen explains that Tony had learned of something illegal that Caspar was up to and planned to use that knowledge to force Caspar to sign a contract guaranteeing adequate protection from pesticides. She explains that she worked in the fields up to the seventh month of her pregnancy and was regularly exposed to pesticides, and Natalie was born with a defective leg. As a result, Tony swore that no other parents would have to see their parents suffer. MacGyver promises to make sure that Tony's dream becomes a reality.
The next day, MacGyver goes undercover to get samples from the fields. While Alex distracts Mendoza, MacGyver manages to get on the migrant bus and out to the fields. He sees the poor working condition and the fact that the workers' drinking water supply is close to the latrine. As he takes plant samples, he notices a jacket with a missing button. It belongs to Lopez, who spots MacGyver looking around and confronts him. He recognizes MacGyver from the protest and orders him off the land. Lopez also believes that MacGyver is an organizer in town to stir up trouble. He says that he was childhood friends with Tony and MacGyver points out that Tony is most likely dead. Lopez angrily orders MacGyver to walk back to town, 20 miles away.
The next morning, Carmen and Alex go to church while Natalie gets MacGyver a pair of sunglasses and nail polishes. He uses the items to make a crude spectroscope and analyze the plant sample he took from the fields. The plants are covered with melting crystals and MacGyver realizes that the Kasabians are using Fixx, a growth enhancer.
Nick is meeting with Mendoza when Lopez arrives to inform him that he's checked MacGyver's fingerprints from the arrest and confirmed the outsider is with the Phoenix Foundation. Nick tells Lopez to meet him at the warehouse. Once Lopez is gone, Nick tells Mendoza that they need to dispose of MacGyver for good.
MacGyver calls Pete to have him confirm his spectrographic analysis. Carmen tells him that Alex learned from a local garage owner that the fender on Nick's truck was damaged the night Tony was run off the road. MacGyver tells her what he's learned and that Pete is sending in a lab team to confirm his results.
As MacGyver calls Pete, Carmen informs him that Alex talked to a local garage owner who fixed the fender on Nick's truck. MacGyver explains that Kasabian is spraying an illegal growth enhancer on the grapes. A team from the Phoenix Foundation is coming to run tests. They figure that Alex will try to get revenge and MacGyver goes to find him.
Caspar learns about the damage to the truck and demands answers from Nick. He warns that his influence with the sheriff only goes so far. He tells his son that he's seen the poisoned workers at the clinic and plans to give in to Tony's demands. Nick warns that they could lose their entire harvest and admits that he's been using the growth enhancer without telling his father. He drives off to clean up the mess while Caspar wonders why he wasn't told.
MacGyver goes to the warehouse and finds Alex preparing to ignite the gas tank on a tractor. MacGyver stops him and tells him that Tony wouldn't have wanted anyone hurt. Alex reluctantly agrees and says that the Kasabians will pay off the inspectors unless they can get more samples of the growth enhancer. They break in and find the growth enhancer hidden in cans of maple syrup. Nick and Mendoza capture them and arrange their "accidental" deaths. They tie MacGyver and Alex up and lock them in a recently-drained wine vat that was pumped clean using carbon dioxide. The carbon dioxide sinks to the bottom and they'll suffocate. Nick will then take off their ropes and claim they broke in and trapped themselves in the vat.
Once Mendoza and Nick leave, MacGyver inches his way over to the interior metal ladder and breaks off a rung. He and Alex use the ladder pipes as a snorkel to breathe the oxygen at the top of the tank. MacGyver then cuts himself free on the sharp ladder edge, frees Alex, and they climb out the top. When Nick and Mendoza return, MacGyver and Alex jump them. Alex manages to knock out Nick while MacGyver uses a spray hose to shoot water at Mendoza, stunning him.
Lopez arrives and holds MacGyver and Alex at gunpoint. Nick orders Lopez to kill them, but MacGyver reveals that they found the button from Lopez's jacket where Tony was killed. Lopez, realizing he's been set up, points out that Tony borrowed his jacket the night Tony was murdered. He prepares to shoot Nick to get revenge for the death of his childhood friend but Caspar arrives with the police and tells his son that it's all over.
MacGyver stays in tony for Tony's funeral. Afterward, Alex and Carmen thank him. As he leaves town, a series of news stories confirm that Nick is being indicted for murder, Caspar has pledged to open up his fields for testing and will encourage the other owners to do likewise, and the government has burned the contaminated fields.