While Wilson is in his jail cell he is met by O'brien. O'brien is a powerful man from the inner party. who then brainwashes Winston to believe that the government is amazing and to never have his own thoughts. Wilson goes through psychological torture during this time and you really see how brutal the government is.
O'brien brings Wilson to room 101. Room 101 is where you see your greatest fears. O'brien threatens to put rats, Wilsons greats fear, in his head so they eat his face to get out. Instead Wilson agrees to let the government take control of him and he tells O'brien to do it to Julia instead.