House creates a miniature racetrack made from medical supplies around his office to race toy cars. Cuddy reminds him that there are patients waiting for him. She is with Morgan West, a nurse at an old age home who complains of having felt run down all winter. Suddenly, Morgan falls to the floor in a seizure as green-colored urine spills down her pants.
After searching the nurse's office for toxins, Taub and Kutner return to the team with a bottle of Methylthioninium chloride, which can turn urine green. Taub thinks that the nurse faked her seizure. House won't admit that he was tricked and considers phenol poisoning from carbolic acid in her cough syrup. He prescribes charcoal hemoperfusion for the poisoning. House tells Kutner that he only wanted to disprove Taub.
House uses a portable strobe light to induce a seizure in Morgan. She has the seizure, but House realizes that she is indeed faking. He can't stand that Taub was right. Morgan pleads with House, explaining that the resident cat at the nursing home predicted her death.
Taub runs into an old high school classmate named Neil Zane who is coming in to the hospital to be treated for a fall that left him dizzy. Taub treats him, and Neil explains that he is the CEO of a medical device company. He wants to take Taub out to thank him.
Morgan brings the cat to House and says that it is known for sleeping next to people that are about to die. The cat sat with her yesterday. House is dismissive but Morgan begs for his help. Suddenly, she suffers a bronchospasm. Foreman says that this time she is not faking.
Cuddy and House watch a news story about the cat. Cuddy gives him twenty-four hours to prove that her illness is real. The team discusses the possibility that the cat can predict death. Foreman suggests that maybe the cat is a carrier for something that kills the patients, such as Larva migrans. Taub pulls a cigar case out of the trash. House asks him whether a CEO sending him a box of Cuban cigars is connected to Taub's money troubles in the stock market. House tells the team to scope Morgan for worms in her lungs.
In the hallway, Taub and Kutner talk about his marriage and his loss of net worth when Thirteen reports there are no worms in Morgan's lungs. House, followed by the team, brings a crash cart to the room where coma patients are kept. He opens the crash cart and lets the cat out of the drawer. They watch the cat climb to the bed of one of the patients. Kutner seems a little uncomfortable around the cat. House orders a methacholine challenge on Morgan to check whether she has an airborne allergy problem.
When she spots a litter box in his office, Cuddy tells House to get rid of the cat. He replies that, with his disability, he can't always make it to the men's room. She wants the patient discharged. So House escorts Morgan out of the hospital in a wheelchair. He takes her to the smokers' area, where he blows cigar smoke in her face and tells her that she is too superstitious. Morgan recounts that, after her stepson died in a car accident, she turned to things outside of science for comfort. House notes a rash on her neck, and Morgan starts to have trouble breathing. He brings her back into the hospital.
House diagnoses Churg-Strauss disease to the team. He tells Taub to clean out the kitty litter box. Taub gets annoyed and walks out. Kutner grabs his bag to go run a test on Morgan and finds that House had hid the cat in it. House has Thirteen start the patient on steroids.
Taub is in Neil's large office, drinking and complaining about his life. He examines a prototype of a surgical tool and gives his advice on it. Neil then opens a bottle of pricier alcohol.
Meanwhile, Morgan's urine comes out brown. As the team discusses this development, House has surrounded them with things associated with bad luck -- a ladder, an open umbrella, spilled salt. Taub talks with House privately, and House knows that he has started to miss the money he used to make. He thinks Taub is trying to get fired.
House shows Morgan that the coma patient selected by the cat to die has not died. He tells her about a 19th Century preacher that misled his followers. Every time he was proved wrong, his followers believed him more.
Afterwards, Wilson approaches House and accuses him of making this whole case a social experiment. They go to the pediatric oncology wing, where Wilson stops House before he can let the cat pick one of the children.
As the team scans through images of Morgan's intestines to look for cancer with the team, House uses a pocket laser pointer which doubles as a cat toy. He speculates that skin cancer could have metastasized to the intestines. Kutner follows House and Thirteen out the door, but the cat blocks him. He turns around and opens up the side door to avoid the cat.
Kutner calls House in the middle of the night to warn him that Morgan has spider veins on her back. House says this means Cushing's disease. Kutner also informs him that the coma patient chosen by the cat has died. Kutner believes that the cat does know something.
With the cat missing, the team searches the bushes around the building and they discuss the Cushing's source -- the kidneys or the brain. House is out of breath and suddenly coughs blood onto Kutner's face. It's really cranberry juice and meant to scare Kutner. House wants Chase to do a venous sampling in Morgan's brain to look for Cushing's.
Taub has lunch with his friend Neil, and asks to come work for him so that he can leave the hospital. Neil says that there are no positions open, so Taub offers to invest in the equipment instead.
House is in the morgue examining the dead coma patient when Chase, Foreman and Wilson come in to report that Morgan went into cardiac arrest during the venous sample procedure. House says they need the patient to decide if she wants her pituitary gland removed as a remedy.
Chase explains to Morgan that Cushing's is an overproduction of the hormone cortisone. Drugs can treat it, but removal of the pituitary gland will do more. She wants the surgery. Morgan believes there is a reason for everything, including getting sick. If there is no bigger purpose, then she does not want to live in that kind of world.
As the surgery begins, Taub tells House that he is quitting. House rejects his resignation, but says that Taub will eventually come crawling back. House wants him to bring donuts when he does.
In his office, House sees the cat sitting on the warm keys of his laptop. House checks the video of the nursing home and figures it out.
At the medical device offices, Taub waits impatiently to meet his friend, only to find out he was not the CEO at all but a temp receptionist. Taub was not the only one who cured his dizziness problem. Taub looks at the check Neil was ready to hand over to a con man.
House tells Wilson that the cat was not predicting deaths. It was merely sitting on a warm spot, such as a feverish patient or a heating blanket. It also meant that Morgan was overheated. House and Wilson realize that what she really has is a corticoid-producing carcinoid tumor which mimics Cushing's in the appendix. House calls the operating room to stop the surgery.
As Morgan readies to leave the hospital, House stops by to see her. She thinks that the cat sat on the laptop for a reason. She mentions the preacher he had referred to had started the Seventh-Day Adventists, a major American religion.
House retreats to his office and finds that the cat had peed on his chair. He blames Kutner and walks out. Thirteen is impressed that Kutner got a cat to urinate. Yet, it wasn't a cat that did it.
Taub returns downtrodden to the hospital and passes by House. House turns to look back at him. Taub sits down in the office and shares a sad look with the cat, holding the box of donuts.