A family arrives for an appointment with House even though it's a walk-in clinic. They claim to have a letter from him about the appointment, which is odd because House doesn't write letters. It seems that Dr. Cameron wrote the letter and signed House's name to aid the family.
House agrees to see the patient. Dan is a 16-year old who has the sudden onset of double vision and night terrors. House says that post-traumatic stress and sexual abuse are two common symptoms. Dan, a high school lacrosse player, admits that he was recently struck in the head. House tells the kid to get some glasses to correct the double vision and ride out the concussion that's causing the night terrors.
As the kid is leaving, House notices Dan's foot twitch and he asks if he's tired or about to fall asleep. He isn't, and House knows the myoclonic jerk is common when a person is falling asleep. The body misinterprets a falling pulse as dying and jolts you awake. House instructs his staff to admit the patient.
House bets Dr. Foreman that the dad isn't Dan's biological father. They can't rule out genetic causes just yet. During the first night, the patient has another night terror, which is recorded on a polysonagraph. But a series of scans and tests show no explanation for the symptoms. House re-examines the MRI and orders another test that shows there is significant blockage. A shunt is inserted to relieve the pressure. After surgery, it turns out what they thought was the issue was only a symptom of something larger. Is it Multiple Sclerosis?
That night, Dan goes missing from his bed. Cameron, Foreman and Dr. Chase set off on a search, eventually finding Dan on the roof. Dan thinks he's on the lacrosse field walking around. The doctors tackle him moments before he wanders off the edge of the roof.
The next morning, House is confused by Foreman's report from the roof. House is thrilled because this means Dan doesn't have night terrors -- and thus, is not suffering from MS. Dan must have an infection in his brain, which House thinks is neurosyphillis.
As Cameron and Chase inject penicillin into Dan's brain, he begins having another attack of voices in his head. The auditory hallucination disproves neurosyphillis.
House orders more tests to read Dan's brain. He notices that the parents have left their lunch behind in the hospital, so House takes a sample to run a DNA test. Cameron finds that neither of them are Dan's biological parents. He's adopted. Was his birth mother vaccinated?
House thinks infant Dan caught a basic measles virus that mutated and reappeared 16 years later after settling into his brain. He suggests injecting a needle into the boy's eye to do a biopsy on his retina.
That frightening test reveals the mutated virus which requires a dangerous brain surgery. However, the surgery if effective and Dan will be fine. Turns out Dan already knew he was adopted after doing his own research in the fifth grade.