Simon Lawson takes his six-year-old daughter Emily to the park. She wants to go on the carousel by herself and Simon reluctantly lets her, warning her not to tell her mother. As her father films her, Emily rides on the carousel but her nose starts bleeding. When her horse comes around, there’s no sign of Emily on it. A desperate Simon runs onto the carousel and finds Emily, unconscious, in the center.
House tracks down Wilson at an oncologist’s office, going over scans of his tumor. House insists on staying, claiming it’s revenge for all the times that Wilson wouldn’t leave him alone, and promises not to tell anyone that his friend has cancer. Wilson finally gives in and House pours himself a drink and explains that he’s taking vacation time.
Foreman calls the team in for differential and they become nervous when they realize that House is taking a vacation. Their superior tells them that they’re taking Emily’s case, and that she has a rare genetic A-T mutation. The doctor with him, a developmental geneticist, explains that she’s an expert on Emily’s condition. Chase realizes that Elizabeth’s last name is Lawson and that she’s their patient’s mother. Elizabeth admits that she is but she’s there as a doctor, and that what they’re seeing is not a normal progression of the mutation. When the team toss out some basic diagnoses, Elizabeth tells them that Eric told her that they were the best and that she’s already considered the obvious. Park suggests Wegener’s granulomatosis and Elizabeth agrees that it’s a good fit. However, she tells the team that they’ll have to do a MRI because the A-T makes Emily susceptible to radiation from x-rays. As Elizabeth leaves to prepare the MRI, Chase points out that she could be a problem but Foreman makes it clear that Elizabeth will be working with the team whether they want her or not.
Wilson meets with his oncologist, Dr. Michael A. Kondo, who advise radiation treatment three days a week to shrink the tumor so that they can remove it. If that doesn’t work, he advises that they then use chemo. Wilson disagrees, insisting that he receive radiation and chemo simultaneously. When Kondo refuses, Wilson stalks out to get a second opinion. Kondo asks House to convince Wilson to take the treatment, but House tells him that his friend is right and goes after him.
In Emily’s hospital room, Simon and Elizabeth argue about his taking her to the park. Taub and Adams come in and Elizabeth explains that Simon had Emily for the week and that was when the girl collapsed. She then prepare to take her daughter to the MRI chamber.
After House gets Wilson drunk while playing Battleship, House asks his friend why he stormed out earlier. Wilson insists that he wasn’t but House points out that Kondo was right, and that every day Wilson waits gives the tumor another day to grow. Wilson tells House that he doesn’t want him around and walks out.
As Taub and Adams run the MRI, Emily admits that earlier she was pretending not to hear her parents argue. Taub admits that his children pretend to be asleep when he argues with his wife, but quickly shuts up when Emily asks if he’s still married. Adams objects to how Elizabeth treats her daughter, referring to her as “the patient,” but Taub suggests it isn’t unusual given that Emily is expected to die by age 20. When Emily cries in pain, they run in and discover that her fingers and toes are turning blue from lack of circulation.
The team goes back into differential after restoring the girl’s circulation. Adams suggest stress, pointing out that Emily heard her parents fighting. However, Elizabeth notes that Emily has heard them fighting plenty of times before and doesn’t suffer from stress because of it. She suggests heavy metal poisoning brought on by the paint in the old apartment that Simon recently moved into. Chase disagrees, believing that it’s lupus, but Elizabeth overrides him using her parental authority. She orders chelation therapy and goes to the apartment to do environmental tests, and Chase suggests to his teammates that they should treat Elizabeth just like any other mother of their patient. He and Adams go to Elizabeth’s house and discover that she’s converted the basement into a laboratory to experiment on her daughter. They find a cabinet filled with an experimental antibiotic, LEX-2, and figure that Elizabeth has been administering it to her daughter.
House persists and visits Wilson later, telling him that he’s checked with four other oncologists that Wilson went to. Each one reported that Wilson wants chemo immediately at a level high enough that there’s a one in three chance that it will kill him. House figures that Wilson didn’t want him to know because he’s already found someone stupid and desperate enough to administer the chemo. He then searches Wilson’s office and finds the bags of chemo that Wilson plans to administer to himself. Wilson says that he was going to take them to his place and do it, and House threatens to cut open the bags. His friend asks him to stop explaining that he wants to go the extreme route now while he’s healthy enough to give himself a better chance of survival. When House points out that the chemo is just as lethal as the treatment, Wilson shows him the toys tokens he has from other patients, including a young boy, John Taylor. All of them died despite the high chance they were supposed to have of survival. Wilson doesn’t want to take any chance of dying alone and miserable in the hospital. House tells him that he’s an idiot... and then volunteers his own place for Wilson to take the treatment.
Chase takes the LEX-2 to Foreman, who calls in Elizabeth and confronts her with what they know. She explains that she tested the antibiotic on herself first to make sure there were no ill effects, and then administered it to her daughter. It would have taken five years for FDA approval of the drug, and Emily would have been long dead by then. However, Foreman has checked the current research and tells her that tests have confirmed that the drug causes renal failure. As Elizabeth realizes that she’s made her daughter worse, Chase says that they’ll do an ultrasound renal biopsy to check for liver damage and hopes that the damage is reversible.
At House’s apartment, House offers Wilson a toast to all the pain and suffering that he’s going to go through as his body fights the chemo. He then asks his friend what they’re doing, and Wilson hands him the first chemo bag.
While Chase does the biopsy, Simon tries to reassure Emily. Elizabeth is there as well and watches over her daughter. Emily starts coughing up blood and Chase confirms that it isn’t her liver as they suspected.
As House serves Wilson some soup, Wilson thanks him for taking the risk given his parole status. House tells him that he’s already made a plan to bury Wilson’s body if he doesn’t survive the chemo. As Wilson begins to suffer muscle spasms, he admits that he hoped to have a family to look after him when he got old or sick. House assures him that he has what he needs: painkiller, and lots of it. He hooks both himself and Wilson up to a morphine drip and they sit back and relax.
Back in differential, Chase figures that they’re dealing with side effects from the LEX-2 treatment. Taub suggest a clot caused by the carousel fall and Elizabeth seizes on it, ordering heparin to prevent an embolism. However, they’re interrupted when they get a page that Simon is checking Emily out. When they go to see him, the parents start arguing because Simon wants to take his daughter to a new hospital. Chase points out that they’re frightening Emily. Once Chase takes her away to get some candy, Taub warns Simon that they’re treating for a clot and that new doctors wouldn’t get up to speed in time to save her. Simon is angry that Elizabeth is treating their daughter like a lab experiment and points out that she doesn’t know anything about their daughter’s life outside of the basement lab. Elizabeth defends her choices, pointing out that Simon doesn’t know anything about Emily’s medical conditions. Simon says that he doesn’t care about letters and numbers, but Elizabeth reminds him that if she doesn’t find a cure then their daughter will die. Simon begs her to save Emily and then walks away.
When Wilson wakes up, he finds a young boy sitting in the room with him and no sign of House. The boy says that he just walked in, but he’s playing with the toy that Wilson had in his office that belonged to his patient, John Taylor. John reminds Wilson that he promised he would go home and asks why he died if he didn’t do anything wrong. Wilson wonders if he’s dead and House shakes him away, saying that it just feels that way.
Taub, Park, and Elizabeth run a MRI and Taub tells the mother that it’s easy to forget what matters when it comes to children. Elizabeth defiantly insists that she hasn’t. They confirm that Emily doesn’t have a clot, but they do discover that she has jaundice due to liver failure. Back in differential, Taub reports that they found a block restricting blood to Emily’s liver. Elizabeth figures that they’re just seeing the end result of the A-T mutation and finally realizes that she can’t be objective. Once she leaves, the team tosses out differentials. Taub suggest advanced Lyme disease and Chase realizes that they wouldn’t have picked it up on the test in its advanced stage. They wonder why it would have become active and Adams realizes that the LEX-2 antibiotic has been keeping it in check until Emily was taken off the drug. The team orders amoxicillin to treat for the Lyme.
House warns Wilson that his white cell count is dropping and their out of morphine. He tells his friend that he’s been using his personal painkillers but assures him that he has plenty. Wilson isn’t convinced but House gives him his Vicodin and then limps out into the kitchen. Once he counts his last few pills, House pours himself some whiskey instead.
Elizabeth and Simon sit at Emily’s bedside and listen as Chase and Adams tell them about the Lyme. When Elizabeth insists that Emily has never been out in the woods to be exposed to Lyme, Simon admits that he took her out there once. Elizabeth takes the news surprisingly well, saying that they can’t protect Emily from everything, and tells the doctors to perform a LP to confirm the diagnosis.
When House is out of the room, Wilson pulls out the medical sensors and tries to crawl to the bathroom. When House finds him and reminds him that he’s wearing adult diapers, Wilson refuses to let his friend change him and collapses in a heap on the floor. He admits that he’s pathetic but that he was fooling himself and all of his patients all of the years that he told them not to bother finding an answer. Wilson says that he should have been a self-centered ass like House. When House points out that Wilson would still have cancer, Wilson says that he would be that he would have deserved to have it.
As Chase and Adams perform the LP, Emily points out that her parents are fighting because of her and wonders if they’ll get back together once she dies. Her arm suddenly goes numb and Chase confirms that she’s having a stroke.
As Wilson’s condition worsens, House tells his friend that they have to go to the hospital. Wilson makes him swear not to go there, insisting that he’d rather die in the apartment than in a hospital. House reluctantly promises not to take him there.
The team tries to work out what is happening to Emily, wishing that House was there. Park suggests cancer but the others note that cancer wouldn’t present and kill Emily in three days. Chase finally realizes that it’s a tumor in the chest, blocking blood flow both ways and causing all the symptoms due to lack of blood. Chase tells the parents that they can remove the tumor surgically and that they should hope that it’s benign.
The next morning, Wilson wakes up, having gotten through the worse. House tells him that now they have to wait seven to ten days for the tumor’s swelling to go down, and then they can rescan and schedule surgery to remove it. Wilson apologies for what he said earlier but House says that he didn’t even pay attention and complains that his leg was hurting him. As House helps him to the bathroom, Wilson realizes that the pain he went though is what House goes through every day of his life. House agrees but says that at least he doesn’t have cancer.
Chase informs Elizabeth and Simon that the tumor was benign and that Emily is fine now that they’ve removed it. Emily wonders if she’s cured but Elizabeth is forced to tell her that she still has the A-T mutation and will still most likely die by the time she’s 20. Simon says that they can’t let that stop them and suggests going to the aquarium. Elizabeth asks if she can go to and Simon says that she’s always been welcome.
Wilson and House arrive at the hospital and Wilson says that he’ll see House later at the cafeteria. House leaves without more than a simple acknowledgement. However, when Wilson goes to his office, he discovers that House has sent him a gift: photos of him all of the time that he was unconscious, with prostitutes surrounding him. Laughing, Wilson studies the pictures with awe and amusement.