A family arrives at the clinic, claiming to have an appointment with House even though it's a walk-in clinic. They even have a letter that is supposedly from House, although House doesn't write letters. House realizes Dr. Cameron wrote the letter, but agrees to see the patient anyway. Dan is a 16-year-old lacrosse player who has been suffering from double vision and night terrors. House says that post-traumatic stress and sexual abuse are two common factors. Dan admits he recently suffered a head injury during a game of lacrosse. House tells him to get glasses for the double vision and to just deal with the night terrors until his concussion passes.
Later, as the kid and his family are leaving, House notices Dan's foot twitching. House asks him if he's tired or is about to fall asleep. He isn't. House says the myoclonic jerk is common when a person is falling asleep. The body misinterprets the falling pulse as dying and jolts you awake. He tells his staff to admit the boy right away.
Later, House bets Dr. Foreman that the dad isn't Dan's biological father, and they can't rule out genetic causes yet. That night, Dan has another horrifying night terror that House is cutting his toe off. The night terror shows up on the polysonagraph. However, the tests give no explanation for the symptoms. The MRI shows that there is significant blockage, and a shunt is inserted to relieve the pressure.
That night, Dan goes missing. After a search through the hospital, Cameron, Chase, and Foreman find him on the roof. Dan thinks he's on the lacrosse field. Right before be nearly walks off the edge of the roof, Chase tackles him. The next morning, Foreman explains the previous night's events to House, who realizes that Dan isn't having night terrors - just hallucinations. This rules out their previous theory of MS, but shows that Dan must have an infection in his brain, like neurosyphillis.
Later, as penicillin is being injected into Dan's brain, he hears voices in his head again. An auditory hallucination disproves neurosyphillis. House later does a DNA test when he gets a hold of the boy's parents' lunches in the hospital. He discovers that neither is the boy's biological parents, and that he was adopted as a baby. It turns out that his birth mother was not vaccinated. Dan caught a basic measles virus from his mother that mutated and reappeared 16 years later in his brain. He suggests injecting a needle into Dan's eye to do a biopsy on his retina. The test results show that he will need a dangerous brain surgery. However, the surgery is effective and Dan will recover. Dan later tells House that he knew that he was adopted ever since fifth grade, but never told his parents.