Female drag racer Casey Alfonso preps for a race. Her crew chief is her father, Lou. As Casey maneuvers the dragster on the track, her eyes begin to blur. She manages to regain control and win the race. At the finish line, a reporter interviews her. Casey's eyes blur once more and she passes out.
House and the Fellows debate whether to take on the case. Foreman suggests that Casey only had severe heat stroke. A federal agent enters and asks for Dr. House. The CIA wants him to consult on a case where an operative might have been poisoned. The agent leads House to a helicopter waiting on the hospital roof.
Brennan and Foreman tend to Casey. Foreman tells the patient that, while she is only dehydrated, they will run another cat scan to be sure. He calls House, who is aboard a private jet. House tells Foreman that he is on a mission for the CIA and he suggests that Casey has Miller-Fisher inflammation. Thirteen comes up with the same diagnosis.
Casey suffers a seizure. She is angry that the doctors cannot make a clear diagnosis. Foreman apologizes to her and she falls into a fever induced delirium. The Fellows debate whether Casey shows signs of MS or Lupus. Brennan and the others challenge Foreman.
At the CIA hospital, House meets a beautiful doctor named Samira Terzi. The CIA has also brought in Dr. Curtis, another consultant from the Mayo Clinic. House is not permitted to know about the CIA patient's background but "John" is clearly unwell and suffering.
All Dr. Terzi admits to knowing is that John has been in Bolivia and his file says that he ate chestnuts. House does not believe that John has been poisoned. He thinks it is pancreatitis. Dr. Curtis argues that John has radiation poisoning, and John is started on treatment for it. House insists that John is hiding that he drinks.
House switches John's medicine to treat pancreatitis instead of radiation poisoning. However, John's progress deteriorates and he falls unconscious. Dr. Curtis admonishes House for his misdiagnosis. House now believes John suffers from Waldenstrom's, a rare blood cancer.
Back at Princeton-Plainsboro, Casey's lab results indicate the possibility of both MS and Lupus. Foreman leans toward MS, but Amber and Taub secretly consult Cameron about the Lupus. Foreman is angry when he finds out that Amber and Taub start treating Casey for Lupus, approved by Cameron. This is in addition to treating the patient for MS. They rush into the patient's room when she says she cannot feel her legs.
Foreman argues that Taub and Amber's steroid treatment could have overloaded Casey's system and made her legs paralyzed. Taub suggests botulism. Brennan argues for polio even though there have been no U.S. cases for decades. This is similar to the polio cases he has seen in the Third World. Foreman clashes with Brennan and starts treatment for Botulism.
Cameron finds Foreman waiting for her in the ER. He has dismissed her patient. Although he really did not do that, she knows he only said it to let her know how it feels to have another doctor interfere in a case. When Cameron complains to Chase, he tells her that she needs to let go of working with House. The Fellows test food from Casey's refrigerator for Botulism. Brennan wants to check for Polio.
House calls Wilson to consult on John's cancer. Wilson doesn't believe that he is really at the CIA. House offers Terzi one of his fellowships. John is feeling better, but when his hair falls out, House realizes he may be wrong about the diagnosis. Dr. Curtis chastises House and Terzi. House suggests an herbal treatment.
Brennan brings his test results to Foreman -- Casey has polio. Cuddy asks Wilson where House is. She doesn't believe him and assigns the doctors extra clinic hours.
Foreman apologizes for being stubborn about Casey. Brennan advises administering high doses of Vitamin C. Brennan and Foreman tell Lou about the vitamin remedy.
House also gives John an unorthodox treatment derived from Chinese herbs. As he tells House that he spent forty days of Carnival as an attachÃ�Â© to a female government minister, House realizes that Carnival in Bolivia only lasts eight days. John was in Brazil, not Bolivia. He ate too many Brazil Nuts. The selenium in the nuts caused his illness.
Casey feels her legs again. The protocol of Vitamin C worked. Foreman is stunned. Cameron supports Foreman and admits that she misses the thrill of working with House.
House leaves the CIA hospital, smitten with Dr. Terzi.
The next day in the lecture hall with the Fellows, Foreman brings Casey's file to House. Casey is free of polio because she never even had it. House describes the scenario: Casey had symptoms that seemed like polio because she was poisoned with thallium and then was apparently cured with Vitamin C. Brennan did this to her in order to obtain research for curing polio in the Third World. Foreman was right -- it simply was severe heatstroke.
House won't fire Brennan and he makes him quit instead. He tells the Fellows to listen to Foreman. Cuddy asks House where he has been. At first she believes the lie he gives her, but then doubles his clinic hours in doubt.
Dr. Terzi is waiting for House at the Princeton-Plainsboro entrance. She wants to take him up on his offer. House thinks she is flirting, but what she means is she is accepting the Fellowship offer.