When Matt is rushed to hospital, Margo gets there right away and meets Robert Chase. As the team suspects that Matt may have overdosed, he asks Margo if Matt takes drugs. She insists he does not and says she used a home testing kit on Matt's hair to confirm that he was clean.
Blood tests on Matt confirmed he had some type of organophosphate poisoning. The team did an environmental scan and found an empty can of pesticides. However, Margo insisted that the container had been filled with orange oil because Matt was doing an experiment and wasn't allowed to use toxins. When she learned that if they gave Matt the wrong treatment he could get worse, she refused treatment.
House intervened and brought a form for her to sign confirming she was refusing treatment, and belittled her for her failure to provide consent to the treatment. However, after she agreed, another patient came in with identical symptoms. The doctors realized it couldn't have been the pesticide they thought because the other patient hadn't been exposed to it.
After that, Margo lost faith in Chase, particularly because he admitted to taking drugs as a teenager to attempt to get Matt to admit he took them too. Foreman replaced Chase even though Chase was a specialist in intensive care. However, Margo got mad at Foreman too when he told her that most family members are wrong on medical calls and told him he was as arrogant as House.
Cameron and Chase learned that the bus Matt and the other boy took to school had passed by someone spraying for mosquitos. However, Margo once again refused treatment until the CDC provided a consult. House sent in Cameron to get consent, and after Margo insulted her, Cameron uncharacteristically stood her ground and told the mother that if Matt didn't get better because they couldn't treat him, it would be her fault. Margo once again consented to treatment.
However, the doctors were wrong again - both patients got worse on treatment. The team kept looking for what they might have in common and House finally realized they both might have been wearing new clothes. His hunch was right and tests showed both Matt and the other patient's clothes were tainted with the same pesticide.
The other family consented right away, but Margo resisted once again, waiting to hear from the CDC. House told Chase to call Margo on her cell phone and pretend to be from the CDC. House then went to Matt's room with the treatment, just in case she wanted to change her mind. She talked about the CDC, and House told her that they probably wouldn't be able to give an opinion right away. Margo then got a call, ostensibly from the CDC, which told her exactly what House had said about not being able to provide an opinion. At her wits end, she asked House why he thought he was right. He said he thought he was right for the same reasons that he thought he was right when he tried the other treatments that didn't work. Margo finally gave in.
Matt finally improved and was ready for release. Margo got a real call from the CDC and realized she had been deceived. On her way out, she met Chase and House and told them about the call. House could only say "Ooops!". She then left with Matt. When Matt asked her who the men were, she told them they were the arrogant jerks who had saved his life.