A student named Matt begins sweating and grimacing during a test. He stands up and passes out. His body goes into convulsions. Foreman presents the case to House. Matt has a severe case of bradycardia, which means that his heart rate is falling fast. House thinks it's simply drug use. While Chase is examining the boy, he begins seizing again.
On House's orders, Foreman and Cameron inspect Matt's home for signs of drug use. They turn up nothing, but Cameron does find a jar of tomato sauce with the lid popped. This could indicate a bacterial infestation. House says the seizures rule out food borne toxins. Or drug use, as Foreman points out. They suspect some sort of poison.
Matt is hooked up to an IV of pralidoxime. Chase tells the boy's mother that the blood work is conclusive that an organophosphate is causing Matt's trouble. Suddenly, Matt's heart rate plummets. Chase puts zoll pads on Matt's chest and their electricity brings his heart rate back up.
The doctors are stumped. Foreman mentions an experimental treatment that should work, but they need to know the exact poison. Foreman and Cameron go back to the kid's house to see what kind of pesticides might be used on the tomato garden. Cameron finds an empty can of disulfoton. Chase prepares an injection of disulfoton hydrolase, but Matt's mother insists he only used orange peel oil on the garden. He dumped the disulfoton out because he couldn't use pesticides in his environmental science class. Since the hydrolase would increase the toxicity if they're wrong, Mom begs Chase not to inject her son.
Cuddy tells House that he will need to get the mother to sign off on rejection of the treatment. He changes the legal language to be slightly more condescending when reading it to her. Mom changes her position. But before they can start Matt on the hydrolase, another patient named Chi is admitted with identical symptoms. Although the two have never had any contact, they do go to the same school.
Chase and Cameron inspect the school bus that Matt and Chi both rode that morning. The driver noticed a truck spraying near a pond. The country had been spraying ethyl-parathion to fight West Nile virus. There is a hydrolase for that, but Matt's mother refuses all treatments until she hears from the Centers for Disease Control. Cameron is sent in to talk to her, and she still refuses until an angry Cameron lays it out for her. Mom finally relents.
They administer the hydrolase. Later, both boys go into convulsions. The doctors save them, but the boys are left in terrible shape. It wasn't ethyl-parathion. They were poisoned in the morning at home. What's the answer? The lanolin in acne cream or deodorant? Foreman and Cameron head out on another inspection. They find a 128-ounce bottle of TKO detergent in each house. But Chi's mom says her son wore all-new clothes today that had never been washed. House and Chase salvage Chi's and Matt's clothes from the trash and run tests on them. They test positive for phosdrin. Time for another hydrolase.
Matt's Mom again rejects treatment until she hears from the CDC. House visits her once again. But instead of merely talking, he decides to just sit in the room with the medicine to pressure Mom. As House predicted, the CDC claims they can't diagnose simply by records. The mother agrees to the third hydrolase. Yet Chase had called her using a fake accent to tell her that the CDC had no opinion. The third time is indeed the charm, as Matt and Chi both recover.
Foreman learns that somebody was selling pants out of the back of his truck. The person's second job was at a cornfield. Some pesticide was spilled on the pants, which weren't washed. The boys were poisoned that way.