Hugh Laurie stars as brilliant but caustic New Jersey medic Dr Gregory House in the fourth series of the Emmy- and Golden Globe-winning medical drama. This week, in the first part of the season finale, House suffers short-term memory loss after being involved in a serious bus crash. While his colleagues urge him to rest, House is plagued by the belief that someone on the bus needs his help.

“I don’t know how I got here,” says House. Sitting in the corner of a lap-dancing club, the dazed doctor realises he cannot recall the last four hours of his life. He diagnoses himself with concussion and discovers that he is bleeding from a gash on his head. But even more troubling is his conviction that somebody needs his help. “Someone is going to die unless I find them,” he says.

Stumbling into the street, House is confronted with the scene of a terrible bus accident. The vehicle is lying on its side while paramedics swarm to help the victims. Some 30 passengers were injured in the crash and most of them have been taken to Princeton-Plainsboro Hospital. At the ER, House is checked over by Cameron, who insists he go home to rest. But House is convinced that, prior to the crash, he saw one of the passengers exhibit signs of an illness. Who was it?

In order to kick-start his memory, House allows Chase to hypnotise him. He enters a dreamlike state and retraces his movements before the accident. He sees himself getting drunk in a bar with Amber – which may or may not be a figment of his imagination. The bartender takes the keys to House’s motorbike as he is not fit to drive, which explains how he ended up on the bus.

However, House is no closer to identifying the person in need of his help until, in the ER, the driver of the bus suddenly collapses with paralysis in his legs. House’s team runs a differential diagnosis on the driver while House explores other means of jogging his memory. He uses smell to trigger his recollection, before immersing himself in a sensory deprivation tank. Each attempt gives rise to a new set of hallucinatory scenes – all featuring a mysterious, attractive woman whose significance to the case is unclear. “I’m the answer,” she tells House.

Before House can probe deeper, he is dragged out of the tank by his colleagues and collapses. Scans show the fracture in his head has worsened and he is ordered to stay at home – with a nurse and security guard for company. However, with the bus driver’s condition deteriorating, Cuddy soon has no choice but to recall him.

Back at the hospital, House hits on the idea that the driver has an air bubble in his bloodstream. He theorises that the bubble was dislodged while he was driving and caused him to jerk the steering wheel – thus leading to the accident. The solution is to stick a needle in his heart and remove it – but Cuddy refuses her consent. House promptly barricades himself and 13 in the patient’s room and orders his horrified subordinate to perform the procedure. “Shut up and make a decision!” he tells 13. “Keep standing there, he’s dead either way!”

House is vindicated when 13 successfully removes the bubble and cures the driver. House returns home to sleep, only to be disturbed by another dream about the accident. “It’s not over,” he tells Cuddy. “I saved the wrong person.” House now speculates that the driver’s condition, rather than being the cause of the crash, was in fact a result of it –which means there was somebody else on the bus who caught his attention. “I need to get back on that bus with all 31 passengers to remember who and what I saw,” he declares.

House recreates the scene onboard another bus with hospital staff taking the place of the passengers. Fired up on Alzheimer’s pills to help break through his amnesia, he finally decodes the mystery woman’s message and relives the crash, leading to a heart-stopping revelation...