Nurse Wolf is Manhattan's Queen of Pain - she gives pleasure by inflicting it, gains pleasure from causing it. The neurologist Dr Oliver Sacks is her opposite, a defuser of pain, a comforter. And yet the dominatrix and the doctor operate in similar territory: both are involved in the ritual and theatrical aspects of sexuality. In Nurse Wolf and Dr Sacks, Paul Theroux hears two remarkable confessions. His book offers an extraordinary insight into the 'other' side of New York.