Winston awakes, immobilized and lying on his back, with O'Brien peering down at him. He has no idea how much time has passed, but he remembers being repeatedly beaten and interrogated. Humiliated and terrified, he remembers confessing to crimes he has not committed. Winston senses that O'Brien is directing the beatings, and though he can't be certain, that he has been imprisoned for seven years.
Earlier in the novel Winston imagined himself dying in defiance of the Party. But now he is kept alive, tortured constantly, until he will admit to doing things he did not do, to things that are not real, just to make the pain go away.
O'Brien turns a dial and Winston receives a painful electric shock. The needle is at 40; O'Brien tells him he will increase the amount of electricity if Winston lies to him. O'Brien asks Winston if the past exists. Winston replies that it does. O'Brien responds that the past exists in the mind of the Party only. To become sane, Winston must see through the eyes of the Party.
Winston and Julia had thought that the Party could trick people about history, but could not actually invade or change people's thoughts. O'Brien is saying that changing people's thoughts, that making them see as the Party wants them too, is precisely the Party's goal
O'Brien holds up four fingers and asks Winston how many he sees. Four, says Winston. If the Party says there are five, says O'Brien, how many are there? Winston says there are four. O'Brien shocks Winston, again and again, then provides drugs that ease the pain. Winston comes to love and depend on O'Brien, because O'Brien alone can ease the pain. O'Brien informs Winston that his goal is not to extract a confession or punish him, but to cure him—to convert his thinking to that of the Party.
Finally, after more torture, Winston gives O'Brien the answers he wants: that Oceania has always been at war with Eastasia, that he invented the photograph of the three traitors, and that he sees five fingers instead of four. Winston begins to understand and practice doublethink, to refuse to believe what he knows is true, and to truly believe what he knows is not.
O'Brien's torture-driven training begins to take hold over Winston. Winston is not pretending that he sees the five fingers. He has been so brutally tortured that is in fact what he sees. The Party is controlling his reality.
O'Brien gives Winston permission to ask him some questions. Winston asks what has happened to Julia. O'Brien says she betrayed Winston and was quickly converted through torture. Next Winston asks if Big Brother exists in the same way that he, Winston, does. O'Brien responds that Winston does not exist. Winston asks if the Brotherhood exists and O'Brien answers that he will never learn the answer to that question. Finally, Winston asks what is in Room 101. O'Brien says that everyone knows what is in Room 101.
O'Brien says that Winston does not exist because he is "training" Winston to see and think as the Party wants him too, to, basically, merge with the Party and lose his individual identity to that collective identity. Room 101 continues to be established as something to be feared.