Dan is playing lacrosse when suddenly his vision blurs and everything seems to slow down for him. Another player slams into him and he falls to the ground, dazed.
House is hiding out in the clinic examination room, refusing to see patients so he can avoid the last five minutes of his shift. Wilson finds him and is surprised to learn that House has no cases and his differential team is sitting on their hands doing nothing. As House leaves, Dan and his parents approach him and say they got an appointment. When House informs them it's a walk-in clinic, they show him the letter they received confirming that he'd see them.
House confronts Cameron, who signs his name on the letter. She explains that Dan couldn't get in and House was ignoring their requests. She describes Dan's symptoms of double vision and night terrors. House is intrigued by the night terrors and goes to see the family and examine Dan. He's been having night terrors for three weeks and tests his mental function. He then explains that he either suffers from posttraumatic trauma or sexual abuse: the two most likely causes. Dan insists that there was no abuse and he was hit in the head. However, Dan's father insists that they had him scanned and there was no concussion, but House figures the ER screwed up. When Dan says he had double vision before he was hit, House tells him he needs glasses.
As House walks away, Cameron accuses him of enjoying taking apart her case, but he insists that he wanted to make sure there was no sexual abuse. However, House notices Dan's legs twitching repeatedly and goes to talk to Dan. He asks if Dan is tired and when Dan denies it, House points out that he's having a myoclonic jerk that occurs when someone is asleep… and Dan is awake. He tells Cameron to admit Dan.
The team begins differential but House notes they don't even have an accurate family history. When Cameron protests, House notes that Dan's father isn't his biological father. He offers a bet of $50 and Foreman accepts, and raises it to $100. Chase suggests it might be systemic and doubts the parents' observation that the parents were able to identify night terrors correctly. House agrees and orders a polysomnograph for Dan at the hospital.
That night, the team place Dan in a bed and hook him up to monitor his sleep patterns. Dan has a night terror that House has come in and is restraining him. House then starts preparing to amputate Dan's toe as he screams in terror within his dream. Chase and Foreman confirm that it's a night terror.
The team runs a series of tests but they all show negative. House looks at the MRI and tells the team that the slightest thing is significant. Chase suggests a meningeal enhancement caused by viral meningitis. House congratulates Chase on figuring he saw something on the MRI and took a guess at what it was. House then points out that there's some bowing between the two halves of the brain. Foreman believes Dan moved during the MRI but House points out that it's not possible. There's pressure causing the symptoms, and orders a radionucleotide cistenogram to reveal the blockage.
Foreman injects the material into Dan's spine via a lumbar puncture so it travels up to his brain. As he does so, he notices Dan's eyes don't match his father's. As he and Chase check the results, he tells Chase what he's found but admits it's not conclusive. They wonder how they can convince the parents to let them conduct a DNA test. House arrives as Foreman confirms there's blockage, and Chase orders surgery to put in a shunt to relieve the pressure. House sarcastically compliments them and leaves.
At the clinic, House is treating a young mother whose child's face has swollen up. He notes that there are no vaccinations and she explains that she thinks vaccinations are a scam by the pharmaceutical companies. House tells her she's an idiot and then admits the child only has a cold.
As House leaves, the team informs him the surgery went fine, but they've confirmed the bowing is a symptom of multiple sclerosis. However, Cameron disagrees with the diagnosis and notes it will take months for a definitive diagnosis. House admits it's come on suddenly. However, he still orders immediate treatment, tells them to tell the family, and goes home.
Chase tells Dan and his parents he probably has MS and warns that there's not much they can do as the nerves are stripped down, causing pain.
That night, a nurse checks on Dan and discovers that he's left his bed. The team confirms that he's still in the hospital and they spread out to search. They call House, who finally comes in. Foreman greets him and House points out that there's not much he can do to help. He also tells Foreman not to tell the parents, and as he leaves says to have someone check the roof because the orderlies prop the door open to get a smoke.
Dan believes he's on the lacrosse field at night. Chase appears and asks if he's okay, and tries to convince him there are possible treatments. He then insists they're on the roof of the hospital and Dan is hallucinating. Dan starts to turn and fall and Chase tackles him.
The next morning, House is coming in and Foreman tells him what happened as he leaves. House is intrigued by the fact Dan was conscious and has Foreman come back with him into differential. He tells the team that the hallucination confirms that Dan doesn't have MS because he was conscious, meaning no night terrors. House explains it must be a brain infection and believes that it's caused by neurosyphilis and orders IV penicillin. However, they have to inject it into the brain and it could herniate the brain stem. House points out they already put in a shunt and tells Foreman to administer the penicillin via lumbar puncture.
As Foreman administers the penicillin, Dan's father wonders how he could get neurosyphilis without sex. Foreman admits it's possible, but rare.
In the clinic, House treats a patient, Funsten, who has a knee infection and apparently tried to relieve the pressure using a nail file. House offers him some Vicodin and asks why he's in Princeton. When Funsten wonders what House is asking question, House points out that Funsten lives 70 miles away and drove by two hospitals. He figures that Funsten has sued other hospitals and they won't take him, and now he has a real medical emergency. However, House offers to treat him anyway.
As House tells Wilson about the clinic patient, Cuddy comes by and House quickly switches topics. She wants to know if he told the parents about Dan's rooftop excursion, and then asks if there was a paternity bet. She wants in and believes Dan's father is the biological father. House covertly offers to take her bet: he goes to a symposium and wears a tie if she wins. He gets off clinic duty for a week if he wins.
Chase administers another lumbar treatment and has Dan focus on Cameron's necklace—and cleavage—to distract him. Dan starts hallucinating voices telling him he's going to die and screams in terror.
Back in differential, the team concludes their diagnosis is wrong and they go back to square one. They rule out basics and House comes up with a new idea: they hook up microphones to Dan's brain and let it talk to them. He goes outside to chat with Wilson, who notes that House panicked. House admits he did, but his idea sounded good. Dan's parents come out with lunch and demand to know why he's doing nothing. When they accuse him of not checking on Dan, he recites their son's readings from memory, and tells them to hold his hand. He even offers to bus their tray. When they leave, House takes their cups and goes to run a DNA test.
House checks in on Foreman and Cameron as they run tests, and tells Cameron to run the DNA test.
As House leaves, Funsten serves him with papers. House responds by claiming Funsten has gonorrhea and threatens to go public with it. He dares Funsten to get a test and the man grabs for the papers. House refuses to turn them over and promises to see him in court.
The team goes over Dan's results and Cameron realizes that Dan's father isn't the biological father. Much to their surprise, the DNA shows that Dan's mother isn't his mother.
The parents are talking to Cuddy about getting a second opinion when House comes in to tell them that they lied to him. They admit that Dan is adopted, and House points out that he needs an accurate genetic history. Cuddy wonders how House learned they weren't the parents and House admits he sampled their DNA. They insist they gave him the biological mother's history, and never told Dan he was adopted. House asks if the mother was vaccinated. They don’t know, and House explains that during a child's first six months, the child relies on the mother's immuno system.
House explains that Dan picked up a measles virus, but once every million or so times, the virus mutated. The virus hid in his brain for 16 years and then caused subacute sclerosing panencephalitis. They figure that Dan is in Stage I, because Stage II is fatal. He's showing Stage II symptoms and could progress at any time. They can treat with intraventricular interferon, but they'd have to drive a spike into his brain to administer and he can't handle it in his condition unless there absolutely sure. They've given him too many incorrect treatment to get a clean test now.
Foreman comes up with one other way to test: paralyze Dan's eye and push a needle through it to perform a biopsy on his retina. They confirm the virus and Foreman tells Dan's parents. He admits they're not going to understand enough to make an informed decision, and he tells them to authorize the procedure. They agree and they drill and insert the interferon.
House gives Cuddy the $3,200 bill for the DNA test. When she objects, he notes that without the bet, they would never have learned the truth. Cuddy agrees to let him out of clinic duty after he pays for the test. House pays her off with the money he won from the bet.
Cameron and Foreman tell Dan that he's doing fine and confirm that his brain is functioning properly. He admits he knew since fifth grade that he was adopted and points out he had a cleft chin and his father doesn't. They realize that's House knew from that all along. Dan assures them that he's fine wit being adopted and loves his parents.
Later, House watches as Dan scores the winning goal. House considers his cane and his leg. Later, after the field is cleared and everyone is gone, he walks away, limping.