Sixteen-year-old Leona is on an airplane with her father, Crandall. Leona is black and Crandall is white. Crandall has taken Leona in from her troubled mother. Leona hallucinates that water is gushing out of the cockpit to flood the cabin. This is similar to what she experienced in the hurricane that devastated New Orleans. Leona's heart races, then stops. She collapses on the cabin floor.
House's leg is causing him tremendous pain, but when he searches for Vicodin in his home he only finds empty bottles. With tremendous effort, he climbs onto a stepstool to reach a lockbox on the top of his bookshelf. He takes out a syringe and a vial of morphine. As he is about to inject, House hears Cuddy leave a message on his answering machine. She has admitted a teenage girl with cardiogenic shock but no heart attack. House becomes intrigued and puts down the syringe.
House goes to the hospital, and Cuddy informs him that Leona's EEG and EKG are normal, she has no signs of infection and the tox screen came out clean. Her heart looks fine. House realizes he knows Crandall from his younger musician days. Crandall explains that Leona's grandfather was Jesse Baker, a famous jazz musician that they both idolized. Leona lost her mother in Hurricane Katrina and Crandall is her natural father. House is convinced that the mother lied to him because Crandall always was a trusting sucker.
The team tosses out possible causes and Houses asks them to retest everything that was checked in the ER. He considers the possibility of arrhythmia but it would not cause a hallucination. They would have to keep Leona under observation for months to spot another arrhythmia, so House intends to induce one. Cameron thinks it's too risky, but House presents the option to Crandall. House advises Crandall to sign the consent form even though the test is dangerous. He then asks Crandall for a DNA sample so he can run a paternity test. He thinks Leona is just using him.
In the electrophysiology lab, Chase threads a catheter through an artery and into Leona's heart. The sinoatrial node is normal. Yet when Chase pushes into the atrioventricular node, the heart goes into a supraventricular tachycardia. The EEG shows normal brain waves, so there is no hallucination. House asks Chase to reset and continue the test but Chase balks, concerned that Leona's heart is fragile after the last attack. House presses him to do it. As Chase enters the next mode, near the cornary sinus, the EEG goes wild. Leona is now hallucinating. Chase freezes a tiny area of heart tissues near the probe and everything returns to normal.
From her room, Leona hears a woman asking for water. She pulls back the curtain and finds a bloated corpse with water pouring over it. Leona, who is really still in her bed, sits up and screams.
Cameron reports that they haven't fixed Leona's heart. Chase insists that the heart is fine and the hallucination must have another cause. House proposes an atypical seizure rather than a hallucination. As he discusses the case, House repeatedly exits the room to pace in the hallway. The team realizes he's trying to walk off leg pain. House comes back in and tells the doctors the fact that they predicted, found and cured Leona's heart problem means the hallucination should just be a coincidence. What if it was caused by the pain of the arrhythmia? Leona might have a disease that translates pain into bizarre physiological responses like hallucinations,
Picking up on this, Cameron considers the fact that Leona may have an autoimmune disease so she recommends a CRP, ANA rheumatoid factors and cryoglobulins. House believes a PET scan will test her response to pain. House straps Leona into a PET scan, assures her that this won't hurt, then jams a syringe into the meat of her palm. Leona screams, but Foreman reports that the cerebral cortex response is normal. House then jams the syringe into her thigh. Leona begins crying as House grills her about Crandall and her real father. He then bends her middle finger backward as Foreman reports the dorsolateral prefrontal cortex also looks fine. Crandall rushes into the room to stop House, and that's when the PET scan lights up. Leona starts to hallucinate.
They confirm that Leona has an autoimmune disease, but they need to discover which one. House suggests killing them all at once. Cameron points out that this would require replacing her entire immune system. House is fine with that, but a bone marrow transplant requires an exact match and Leona has no siblings. House walks off. Crandall barges into House's office and reasserts that he's Leona's father. Crandall demands that House test his marrow. House tells Crandall that he has been scammed. This is not the first time he's been taken.
House and Wilson watch Leon go through radiation. House says that Crandall is not a marrow match, although he didn't do a paternity test per Crandall's request. A match was found in the marrow registry. House notices black goo oozing out of Leona's mouth. House and Wilson have no idea what it is.
The lab results on the goo come back, but House already knows what it is. True to his suspicions, the goo contained stool and digested blood. He recognizes a reverse peristalsis. In order for digested blood to be in the intestines, Leona must have internal bleeding. There must also be a blockage forcing the material up and out of the mouth. Foreman tosses out liver failure. With no proteins to clot blood, it could leak into her stomach. House realizes that this means they were wrong on autoimmune disease. Nothing would shut down an organ in two hours. He orders a liver biopsy.
House finds Crandall and tells him that they need a liver biopsy, but are not sure what will happen. Leona could die the second they stick a needle into her liver. Foreman and Chase begin the biopsy. The needle is millimeters away from Leona's liver when House pages Foreman with instructions to stop.
In House's office, he plays some of Jesse Baker's music for the team, He wants them to hear an uncut portion when a drunken Jesse rails at an engineer for not tuning his piano correctly. The team is unimpressed, but House points out that the piano was not out of tune. If Jesse was drunk, his playing would be off. He is playing perfectly. Something else is ruining his personality, and House believes his aural perception was off. Combined with Jesse's fatal liver failure, this means he had too much iron. Jesse could have had hemochromatosis, which is genetic.
House takes the doctors to Leona's room and shows them a picture from Crandall's book about Jesse. Leona was thirteen then, but her skin is darker now. House attributes this to grayness from direct iron deposits in the skin and tan from too much melatonin. Both symptoms are products of hemochromatosis. House asks for a SQUID exam to calculate the amount of iron in the blood. He prescribes desferoxamine as a treatment, assuming she will be fine after that. A subsequent MRI does indeed reveal lots of iron on Leona's liver.
Chase starts Leona on an desferoxamine IV, explaining to Crandall that the chelating agent will bind to the iron so that the liver will be able to process it. As the medicine drips into Leona's bloodstream, she starts gasping for breath. Chase urgently intubates. A CT reveals that Leona's lungs are basically swiss cheese. Chase thinks her time is up.
House starts over, asking what is supposed to happen when desferoxamine is introduced. Chase explains that iron is heavy and gets stuck. The desferoxamine bonds to it and acts as a lubricant so the iron can be processed and discharged through waste. Yet now, Leona's waste is heading north, not south. Has the iron moved into her lungs? Oxygen will attach itself to iron, which increases the chances of infection. They had put Leona on antibiotics earlier to prevent infection and try to figure out what else would attach to iron. Cameron brings up neurodegenerative disease with brain iron accumulation, but there are no iron deposits in the brain. Foreman inquires about fungus, and Chase points out that there are 25 antifungals. House asks them to go broad. Cameron says the most common fungus is aspergillis. House orders them to continue ventilation, start a voriconazole drip and hope Leona has aspergillis.
Wilson has a sudden revelation. House did the paternity test, but it came back positive, so House simply dropped it. They get word that Leona's lungs have collapsed because they have diagnosed the wrong fungus. House gathers the team and asks them to consider location.
House goes to Leona's room and informs her that she has a fungus. If she's lying about living in a children's shelter before Crandall rescued her, she could die. Leona blinks, indicating that she was lying. House gives her a pad and pencil, asking where she actually was.
House reports to the team that Leona was holed up in Jesse's recording studio. Cameron deduces that soundproof recording studios also absorb moisture. Hurricane Katrina, with its incredibly levels of mold, created zygomycosis in the studio. House asks for an IV drip of amphotericin B and colony-stimulating factors. He declares for a third time that they've solved the problem and that Leona will be fine. As Foreman hooks up the IV, he tells Crandall the truth about where Leona was.
House visits with Crandall and Leona. He asks Crandall why he thinks he will be a good father. Crandall replies that it feels good. House then chases Crandall out of the room and admits to Leona that he did run a paternity test. Crandall is her father. That night, House relaxes at home with the music of Jesse Baker. He examines the paternity test for Crandall. It's negative.