Maria Palko steps out of the shower and finds a masked man in her bathroom. The man drags Maria to her bed and she fights him off. The man begins struggling to breathe. Maria calls an ambulance for the man, who is actually her husband, Bob. Their rape fantasy had an unexpected end.
Another interesting couple prepares for the day. Wilson is staying at House's apartment during his separation. House is bothered by Wilson's habits, and he orders him out only one night. Wilson promises to be moved by the next day.
At the hospital, Bob explains to Cameron that he has dry throat and a feeling that his tongue is swelling. Two previous doctors tested him for food allergies before referring him to House. The Palkos are remarkably open about their sex life during the examination. They reveal that they recently had a threesome with Maria's old college roommate. House wonders if the problem is actually in Bob's lungs. He orders more blood drawn, a chest VT and a body plethysmograph.
Bob sits inside an egg-shaped body pod, holding a tube in his mouth. Maria watched while Cameron runs the test. Their conversation turns to the couple's unusual sex life. Maria defends the effort, saying that marriages fail because people don't want to change.
The team reports that House was correct in the lung diagnosis. The plethysmograph revealed decreased lung capacity and the CT showed lung scarring. The team is convinced that Bob has interstitial pulmonary fibrosis. However, with all common reasons are ruled out, they don't know the cause. Since Bob's condition is currently stable, House wants to wait until the cause presents itself in another fashion.
Suddenly, bright red patches of skin emerge on Bob's chest. The team reconvenes to figure out what causes itchy splotches and lung scarring. Foreman suggests lupus. House is hit with the realization that heavy metal toxicity might be the problem. House orders the team to search the Palko house. They also need to test Bob's hair for lead, mercury and arsenic. Perhaps the Mexican resort that Bob and Maria vacationed at cooks with such metals. Maybe they recently repainted or made plumbing repairs.
At home that night, House asks Wilson if he thinks somebody could suffer lung damage after eating out of a pot painted with lead paint. Wilson replies that it would require months of daily eating.
Foreman searches the fastidious Palko house and finds an ant. House wants to know what type of ant. When Foreman tells him it was medium and brown, House rules out poisonous ants. A tox screen also disqualifies lead, mercury or arsenic, but House wants the tests run again. The team begins to resist House's thoughts on heavy metals. He orders treatment for lead poisoning.
Chase is performing a scratch test on Bob's back when he patient begins agonizing over a burning pain in his feet. This rules out food allergies. House thinks this is another sign of heavy metals, but Cameron insists that another hair and blood test ruled out any possible exposure. The team is paged to Bob's room. He again struggles to breathe. They attempt to intubate, but Bob begins coughing up vomit. There is too much to be suctioned off, so the team is forced to perform a tracheotomy to help him breathe.
Foreman reports that Bob's urine has elevated proteins and red blood cells. He stands by his theory of lupus, and House insists that the cause is a heavy metal. Foreman wants to run an ANA but House points out that they've already treated for lupus with no results. Unless House can prove his metal idea, Foreman plans to start a new treatment for lupus.
House considers whether Maria is poisoning her husband. He wants Cameron to search Maria, but she objects. House decides to do it himself. He corners Maria and tells her his suspicions. He searches her purse and asks for permission to examine her vagina because it is the only place she could be hiding something since she hasn't left the hospital. Maria, Cameron and Cuddy all refuse to allow the search.
Foreman wheels Bob into an isolation room and the patient immediately seizes. Foreman races into the hallway for the crash cart and shocks Bob back to life. As House and Wilson observe Maria's concern for her husband, House begins to doubt his theory on poisoning.
The team reconvenes in the office. Foreman is confident that what's happening to Bob is the definition of lupus. Chase suggests a different treatment, and House mentions interferon, which treats neither lupus nor heavy metal toxicity. Yet House thinks it's about all they can do right now for a viral infection. House says the lupus treatment has wiped out Bob's immune system which is what invited the current viral infection. Foreman points out that interferon will make lupus even worse. House strongly orders interferon.
That night, Bob and Maria are alone in the isolation room. Bob tells her that he sat behind in her high school to cheat off her during a test. They've had a long history and he loves her. Maria refuses to say she loves him because he's not dying, and she doesn't want to say goodbye. After a moment, she gives in and says it.
The next morning, Foreman tells House that the interferon isn't working. House wants an increased dosage. Yet tests for every virus they can think of are all coming up negative. House repeats his instructions to up the dosage. Later, House looks at a gold wedding band and has another epiphany. He calls Cameron and asks if Maria has a family history of arthritis. When Cameron confirms this, House orders Cameron to stop the interferon, run a heavy metal screen for gold and prevent Maria from using the bathroom.
The doctors are stunned as they read the results of the tox screen. House, meanwhile, races home and pulls a wooden box from underneath his bed. House searches through a selection of small glass vials in the box until he finds the one he's after. At the hospital, the doctors are trying to prevent Maria from using the bathroom. House arrives, looking for Maria. When he founds out she's heading for the bathroom, House barges into the ladies room in search of her.
He finds her coming out of a stall and grabs her hands. House says that the damage to Bob's lungs is permanent, but the coma and kidney damage are reversible. He should also regain all neurological functioning. Despite Maria's complete confusion, House continues. He says that nitric acid, mixed with gold, turns bright purple. Maria's hands are stained purple. House accuses Maria of sprinkling Bob's food with gold sodium thiomalate, an arthritis remedy that's out of date in the U.S. but still popular in Mexico. Maria denies it, but Chase reports that the tox screen for gold was off the charts.
Two police officers walk Maria out of the hospital in handcuffs. Cameron reports that they have started chelation therapy, but Bob will need a lung transplant. House doesn't mind. He's too pleased at having been proven right once again.