House receives a lap dance in a strip club. He looks disheveled and somewhat confused as to why he is there. His vision is weak and he realizes that he has a head injury. House starts to have flashbacks about a bus crash. Although he is uncertain, he believes that someone he saw is going to die. He must urgently get to them. When he walks out of the club, he sees the frenzy of an accident scene. A metro bus is on its side. Emergency workers and wounded passengers are amidst the chaos. House realizes that he was also on the bus. He cannot remember who is the person that needs him.
In the ER, Cameron and Wilson tend to House's injuries. House cannot remember why he was even on the bus. He seeks out the bus driver in the ER and considers whether the man may have suffered a seizure. Instead of resting with his injury, House is determined to recall what happened. He is interested in the other passengers and their problems.
Chase hypnotizes House to see if he can remember anything. Wilson observes. In House's mind, he is on the bus with Chase. Then they are at a bar with Wilson, who asks House why he was drinking alone. What is he running from? Now Amber joins them. House jokes that he can't even have a subconscious conversation with Wilson without Amber butting in. House suddenly remembers that the bartender took away his motorcycle keys because he was too drunk to drive. That is why he was on the bus.
In his memories, House is now back on the bus. A beautiful, mysterious woman is making eye contact with him. He is interrupted by another passenger, a young Goth punk who is coughing. Back in the ER, House finds the punk and tells him that he has a brain tumor because he picked his nose on the bus. House is wrong and is distracted by a commotion. The bus driver cannot move his legs.
The team discuss the driver's symptoms. Thirteen suggests Guillain-Barre Syndrome but Kutner thinks it could be transverse myelitis due to the high white blood cell count in the driver. House has a flash of a memory where a passenger is drinking coffee on the bus. He decides that he needs to smell the bus. Foreman starts the driver on antibiotics for transverse myelitis while House goes to smell the clothes of the passengers collected in a box.
House hallucinates that he is on the bus alone with the driver. He is then among the passengers, and asks the mystery woman why she is there. He is yanked back to reality by Wilson, who orders House to get an MRI. Wilson administers the test to House and they discuss Amber. House has a longitudinal fracture of the temporal bone. House does not understand why it is so important for him to investigate the bus accident.
House is in the cafeteria working when he is struck by a debilitating headache. He arrives at the bus driver's room to find him being helped up by Thirteen and Foreman. The driver clutches his stomach in pain. House suddenly starts bleeding from his ear.
Thirteen places House into an Epsom salt bath to achieve an alpha theta state from sensory deprivation. Inside House's mind, he sees Cuddy riding the bus with him. He crosses this with a sexual fantasy of Cuddy where she is dressed in a naughty schoolgirl outfit and she dances around the bus pole. They go through possible illnesses that the driver may have. When he suggests Parkinson's disease, the mystery woman appears. She tells House that she is "the answer." Back in reality, House is pulled out of the water by the team. He pukes on Cuddy and passes out.
House wakes up in his apartment. On Cuddy's orders, a nurse tends to him while a hospital security guard stands watching. Back at the hospital, the team adds jaundice, low albumin and liver failure to the list of symptoms for the bus driver. Thirteen suggests Wilson's Disease and Taub advocates thyrotoxic periodic paralysis (TPP). House calls in to ask how they eliminated Parkinson's. Taub says that TPP fits all of the symptoms. House wants him to run "the bagel test," where the patient jogs on a treadmill while eating bagels to increase carbohydrates.
Since he's not allowed to participate in the diagnosis, House swipes the nurse's cell phone and calls Kutner who is performing the test. House listens in but does not agree that TPP is the diagnosis even though the driver has passed out.
Cuddy allows House back in the hospital. The driver gets intubated and the team looks for a clot in his lungs from a pulmonary embolism. House realizes that the driver has new teeth caps. The team begins to leave the patient's room to make way for the bed to be pushed out. House closes the door shut and wedges his cane into the door frame. Thirteen and House are left inside. House explains that an air bubble must have been in the driver's gums from dental surgery and it got dislodged while driving. House will move the bubble to the patient's heart and wants Thirteen to suck the bubble out with a syringe. Thirteen agrees to perform the procedure against Cuddy's wishes. Thirteen stabs a syringe into the patient's heart and it works.
Cuddy stays at House's apartment to keep an eye on him. House falls asleep and dreams that the mystery woman is on his sofa instead of Cuddy. She shows him her necklace to nudge him to remember more details. He ties a red scarf around her legs. She is cold. For some reason, he tells her, "Stay with me." He wakes up and tells Cuddy that he saved the wrong person. The bus driver's air bubble was caused by the crash. House had been worried about someone else. House wants to reenact the bus accident with 31 stand ins. Cuddy reluctantly gives in.
At a bus terminal, the doctors wear photos of the actual passengers and sit in the seats from House's memory. House pops a few pills. They aren't Vicodin but Alzheimer's Disease meds to speed up his neuronal firing. He goes back to that night in his mind. The mystery woman asks House to name the material of her necklace. The material is amber, and he realizes who she is.
The mystery woman is now replaced by Amber in an actual memory of the crash. Amber's side of the bus is hit, and she and the other passengers hurdle out of control as the bus rolls and spins. House is injured but he tries to save Amber. A broken piece of metal is stuck in her leg. He wraps her red scarf as a tourniquet. She is cold and he tells her, "Stay with me." House then walks away from the accident scene in the direction of the strip club.
House awakens to Cuddy administering CPR to him. His heart had stopped. House tells them that the mystery passenger on the bus is Amber. Wilson has not heard from her lately, but he assumed she was on call. Thirteen rattles off the physical details of one of the unidentified victims at another hospital. Amber matches the description. She is dying.