first broadcast on November 23, 2004.
A 16-year old lacrosse player starts suffering from double vision, night terrors and frequent hallucinations after being struck in the head. House and his team must diagnose the mystery brain condition which is causing all these symptoms before it progresses to a fatal stage.
House had first dismissed the symptoms as concussion and then suggests that the cause might be post-traumatic stress due to sexual abuse. But then he notices Dan's foot twitch with a myoclonic jerk which normally only occurs when falling asleep. He immediately admits Dan and starts diagnosis with his team.House claims that Dan's father isn't his true biological father and makes a bet with Foreman about it. Soon after, Dan has another night terror. None of the tests show why the night terror occurred, but House finds a large blockage in one of Dan's brain ventricles. House and his team relieve the pressure as fast as they can, but they find that the blockage isn't what is causing the other symptoms. It is in fact a symptom itself.
During the night, Dan is found missing from his bed. Cameron, Chase, and Foreman search frantically to find him, soon locating him on the roof, where he is hallucinating that he is on the lacrosse field. Chase tackles him just before he steps over the edge of the building. House is excited by this new development — it rules out House's previous diagnosis of multiple sclerosis. The new diagnosis provided by Cameron is neurosyphilis. To treat this, they inject penicillin directly into Dan's brain, but during an injection, Dan suffers an auditory hallucination, which rules out this diagnosis. House is stumped by this new development, and admits his problems to Wilson. Dan's parents are angered to discover House having coffee with Wilson while their son is dying, but House rebukes them with his intimate knowledge of Dan's current condition. He tells them to go and support Dan, after which he takes their coffee cups to run DNA tests to decide his bet on Dan's paternity. The tests show that neither parent is biologically related to Dan.
House thinks that infant Dan caught the basic measles virus from his biological mother (who possibly had never been vaccinated) that had mutated, remained latent for 16 years, and reappeared in his brain. Avoiding a dangerous brain biopsy to confirm this unusual case, they biopsy Dan's retina to find the virus, confirming House's diagnosis of subacute sclerosing panencephalitis.