A woman named Cynthia drives her daughter Hannah to the hospital because she slipped on ice. Hannag insists that she is fine. As they speed through a snowstorm, the car is broadsided. With Cynthia unconscious, Hannah dials 911 with a cell phone. The dispatcher asks Hannah is she has any injuries. She looks down, sees a metal rod jammed into her thigh and says she's fine.
At the hospital, Foreman examines Hannah, who's only worried about her mother. House comes by as Foreman is cleaning her wound. When Hannah winces at the soaked gauze, House studies her. He immediately figures out that she has CIPA -- congenital insensitivity to pain. It is one of the rarest conditions on the planet, with only about sixty documented cases. They will need to x-ray to check for internal injuries. Foreman is skeptical, so House whacks Hannah in the shins with his can. Her delayed reaction, followed by her slumped shoulders, tells the doctors everything they need to know.
House petitions Cuddy to let him run tests on Hannah. When she learns about the CIPA, Cuddy realizes that he only wants to find out about his own pain through Hannah's illness. House doesn't deny it, and he keeps pressing Cuddy about the tests. She agrees to x-rays, blood tests and an EEG. Yet she refuses a nerve biopsy, which runs a risk of paralysis. If the EEG shows a problem, then they can talk further.
The doctors try to run an EEG, but it is rendered useless when Hannah screams to see her mother the entire time. They tried to sedate her and couldn't hold her down. She is strong and has no fear. House goes in to see Hannah and he starts trading notes with her on their respective conditions, arguing the difficulties they each face living a life of either constant pain or none at all. When Hannah turns around to show House a scar from sitting on the stove when she was three, House stabs her with a syringe loaded with sedative. He instructs his team to finish the test.
Hannah awakes and Cameron explains that all of the tests came back negative. Suddenly, Hannah's eyes roll back in her head and she collapses. Her temperature is 105. The team analyzes possible causes for Hannah's fever, coming up with nothing tangible. House suggests running a biopsy on the spinal nerve, so he goes to request Cuddy's permission. House tracks her down on a blind date at a coffee house and again asks for a nerve biopsy. Cuddy initially resists, but when House presses the issue she acquiesces.
Chase and Cameron observe surgery on Cynthia, who is not faring well. They decide to keep Hannah in the dark as long as possible. Foreman comes in to discuss House bulldozing a path toward a spinal biopsy, which is a procedure they're greatly opposed to. Chase figures the only chance they have to stop him is if they find the answer first. In an attempt to determine the problem, Chase suggests overloading Hannah's pain receptors until something starts reaching the brain.
Chase hooks Hannah up to a PET scan and has her stick her hand back and forth between two containers of hot and warm water. The test begins and Hannah asks about her mother. Distracted, she leaves her hand in the hot water. By the time Chase is able to pull her hand out, Hannah has second-degree burns.
They put Hannah in a surgical chair with a stereotactic frame screwed into her head to prevent her from moving. She is wired to a series a monitors. Foreman withdraws a needle from Hannah's skull, announcing that he has injected kinase proteins which will replace missing chemicals in her brain and perhaps trigger a response. Another doctor begins drilling into her skull, and Hannah casually chats with Foreman throughout the procedure. Suddenly, her eyes open wide and she starts screaming. Foreman immediately stops the procedure and asks Hannah where it hurts. Hannah smiles, pushes him over and runs out of the room.
Wilson confronts House about Hannah because he is convinced House is only keeping the girl in the hospital so he can study her. Although House claims he is merely curious, Wilson isn't having it.
Hannah goes to the lobby balcony in order to jump. Cameron pleads with her to come down from the railing, explaining that she's having a paranoid delusion. Hannah claims that she can't feel her legs, then tumbles to the floor below.
That night, Hannah sits in bed looking perfectly comfortable. Cameron rattles off the list of her ailments: six broken bones, a concussion, a fever, erratic heart rate and total numbness below the waist. Hannah smiles and says she feels fine. She asks if her mother is out of surgery.
The team examines Hannah's x-rays. Since her spine is clean, they figure temporary paralysis was caused the fall. House allows the paranoia and paralysis to lead him to a neurological issue, so he once again suggests a nerve biopsy. Cameron jumps in with the idea of a thyroid storm, which House is unable to rapidly shoot down. Foreman points out that this thyroid storm makes sense, given her glucose reaction is slow and her potassium is down. House is stuck to disagree, so he calls for an endocrinologist.
House drops by Cuddy's place with the file. She asks why he didn't call Dr. Bennett, the endocrinologist on call. House claims that he did but that Bennett didn't pick up. Bennett's phone must be broken. Despite the fact that she's in the middle of another date, Cuddy reads through the file and shoots down the possibility of a thyroid storm. Then Cuddy steps close to House and asks if he likes her. House is thrown, and he has no answer. Cuddy joyfully points out that she spoke to Dr. Bennett fifteen minutes ago. She finds it interesting that House feels the need to constantly drop in on her when she's on dates.
House returns to the hospital with confirmation that it's not a thyroid storm. He notices that some papers are missing from his desk, so he walks directly to Wilson's office. The team trails him, repeating their warnings about the risks of performing a nerve biopsy. House demands his papers back from Wilson, who asks for some privacy with him. Wilson refers to the article, mentioning that researches recently found a protein that speeds up nerve growth. If that protein was insulated with spinal nerve, it could create a nerve garden. If that spinal nerve came from a CIPA patient, then a doctor might be able to grow pain-free nerves and perhaps graft them onto his own leg. Wilson points out that he would be risking the patient's life, but House counters that the idea is justified. Wilson wants to know whether House really thinks he's the one who should be making this call. Finding his team waiting in the hallway, House instructs them to biopsy whatever nerve they think they can extract with no risk.
After they take a biopsy, Foreman and Cameron are confused because CIPA shouldn't cause this much degeneration. They call in House for a consult. The insulation around the nerve fibers has basically been stripped, meaning the damage is coming from the outside in. House pronounces it secondary demyelination, which means it is not a nerve disease but more likely metabolic. Cameron walks out of the discussion in order to take Hannah to see her mother, who just came out of surgery.
Seeing her mother is quite stressful for Hannah, and when her mother is taken away for a second surgery she cries over a pain in her head. Unfortunately, this tells the doctors nothing because the pain is emotional. House adds guilt to the white board of potential metabolic symptoms, which could be caused by a vitamin B12 deficiency. Yet Foreman notes that the hospital administered B12 as part of a multi-vitamin supplement when Hannah was admitted. House's theory is going nowhere.
House visits Wilson to complain about again being stymied in Hannah's case. House takes a bite from Wilson's sandwich. Wilson jokes that he derives pleasure from beating other hunters to the food. Suddenly, House has an idea.
He rushes into the procedure room where Chase and Foreman are about to sedate Hannah. House grabs the mask, mentioning that nitrous makes a B12 deficiency worse. Foreman again points out that Hannah already received a B12 supplement. House is convinced that somebody else already ate it first, alluding to his conversation with Wilson. House calls for an abdominal MRI. Hannah begins freaking out with another paranoid delusion. House barges into an OR with her.
House cuts into Hannah's stomach without any anesthesia, and he pulls out a floppy, wet, white worm. He continues pulling and pulling, eventually removing the entire 25-foot parasite. A worm like this would have caused anyone else tremendous pain since it would have sunk its numerous claws into the intestinal wall to lock into its host.
That evening, Cameron remembers that it is Valentine's Day and she invites Chase to come to her place. Chase questions whether or not she is settling because she is feeling lonely. Cameron tells him to forget it.