Two 12-year-olds walking home from school sneak into an abandoned building to join their friends for beer and cigarettes. One of the boys, Gabriel Reilich, trips and falls on the old, wooden floor. Later that week, Gabe develops a rash on his arm. His worried mother, Sarah, takes him to the hospital, concerned with the fever he's had all week. Gabe tries to get out of bed, but collapses on the floor.
Cuddy reads Gabe's file to House, who assumes the boy merely has pneumonia. This can only be considered important only because Gabe's parents are big donors to the hospital. Yet when Cuddy describes Gabe's rash as a papular lesion on the arm, House becomes suddenly interested.
He and the team try to figure out which kind of pneumonia would cause this rash. Foreman suggests Chlamydia pneumonia, but 12-year-olds don't have much sex. Could the rash have come first? Then Lyme disease is a possibility.
House instructs the doctors to keep Gabe on cefuroxime, biopsy the rash and gather another patient history.
As Chase takes fluid from the rash, Gabe's father, Jeffrey, angrily demands to know what they are doing. Chase wheels Gabe off for a private conversation. While the two bond Gabe admits to Chase that he fell in the abandoned building and scraped his arm. He also remembers it smelling moldy up in the attic.
Chase is about to head out to take a sample from the building when Dr. Rowan Chase enters House's office. He is Chase's father. Chase brusquely leaves, not exchanging any pleasantries with his father.
After Chase returns with samples of the felt-based insulation between the floorboards of the abandoned building, House realizes that the old insulation is made from animal hair. He then notices Anthrax on Gabe's CT scan.
Cameron rushes out to put Gabe on levaquin and move him to the ICU. Jeffrey can't believe his son has Anthrax poisoning, and he asks about leishmaniasis and filariasis, which he looked up on the internet. Meanwhile, Gabe struggles to breathe.
Foreman sticks a laryngoscope into the boy's mouth to open his throat. Yet he can't insert an endotracheal tube. Chase is about to administer an emergency tracheotomy when Foreman's intubation finally works.
The team tries to figure out what caused the swollen throat nodule reaction. Is it an allergy? House wants to consult with Rowan, Chase's father. Everyone except the obstinate Chase moves off the Anthrax diagnosis and they run tests for sarcoidosis, which makes the body's tissues swell up.
But before Foreman can administer anti-inflammatory medicine, Chase notices that Gabe's rash has turned black. This is a sure sign of Anthrax, even though throat nodules are a sure sign it isn't Anthrax.
Everyone offers dissimilar opinions. Rowan Chase suggests Anthrax plus sarcoidosis. His son insists that both diseases are too rare to occur at the same time, and offers up an allergy plus Anthrax. House thinks the Anthrax damaged Gabe's immune system enough to trigger a dormant sarcoidosis. He instructs them to keep Gabe on antibiotics for Anthrax and start him on methotrexate for the sarcoidosis. They can wait to see what happens.
Jeffrey is furious. He tracks down House and demands to know why he's experimenting on his son without even seeing him. Jeffrey also protests that he gives to the hospital solely to get immediate attention. He shows off his wrist as an example. After six months of diagnoses that told him to rest, Jeffrey wrote a big check and was admitted to surgery for carpal tunnel that afternoon.
Gabe has now developed hideous looking fatty red nodules on his back and the lesions are spreading all over his body. Rowan Chase advocates that it's an autoimmune problem. The body is working so hard on attacking the Anthrax that it's also attacking itself. Autoimmune problems could indicate almost anything, so they start Gabe on steroids and cytoxan.
Chase, meanwhile, conducts a biopsy on Gabe's lesions in an attempt to prove his father wrong. Although Gabe's swelling is down and his skin looks better, Chase shows his father an ANA test that shows no autoimmune disease. Rowan Chase counters that ANAs are unreliable. Chase demands to know why his father is even here.
House tracks down Rowan in the hall. He noticed a blue dot on his neck, which is a tattoo for guiding radiation treatment. Rowan admits to House that he terminal stage four lung cancer.
Chase tests Gabe for every possible autoimmune condition, and the boy senses that he can't move his hand. His right hand and forearm are now paralyzed and the fever has kicked in again. Chase claims that toxic neuropathy was brought on by the cytoxan.
Cameron wonders what brain process would cause paralysis, skin lesions and throat nodules. Rowan realizes that his son's diagnosis -- multiple neurofibromatosis -- might be correct. House orders another CT scan.
The test shows no masses or fibrous tangles. It isn't neurofibromatosis. It could possibly be Burger's Disease, but Gabe has never left the country.
The team considers the parents, and House remembers Jeffrey mentioning leishmaniasis and filariasis, which are two diseases basically exclusive to Southeast Asia. They consider whether Anthrax didn't trigger the second disease, but the hospital treatment or antibiotics did.
House heads to Gabe's room and grabs Jeffrey's wrist. How did he know about those obscure diseases?
House tells Jeffrey that if he doesn't tell the truth, Gabe will die. Jeffrey breaks down and confesses that he spent two years in India. After joining an ashram, he ended up losing all his money. He was too embarrassed to admit his failure to his family.
House tells his staff to run a FITE stain to check for leprosy. This could have weakened Gabe's immune system and enabled the Anthrax. Although the antibiotics they administered would stave off the leprosy, the dying bacteria produce antibodies which eventually attack the body's neural and fat cells. This would cause inflammation and all the other symptoms Gabe was suffering from. House orders Cameron to get the boy some thalidomide.
Gabe improves and his father is also treated for leprosy. That night, Chase sees Rowan off as he heads to the airport. Chase promises to visit him in the next year. Rowan stares at his son but doesn't admit that he likely won't live that long. Chase hugs his father, not knowing that it is the last time he will see him.