IT is only just that an argument about phantoms begin by introducing its own ghosts. Shakespeare's Hamlet and Macbeth prowl the shadows of Charles Dickens's Great Expectations and Peter Carey's Jack Maggs, the novels that are my central subject, and they are plays in which the outraged dead return to reveal the fraudulence of a social imposter. The opening scene of Hamlet contains one of literature's most devastating visitations, who appears to the royal sentinels as they await the midnight return of the apparition that resembles their buried sovereign. Darkness and duty explain only part of the care with which the sentries test the men who approach their post. The play begins with Barnardo's cry, 'Who's there?' and the guard's cautious rejoinder, 'Nay, answer me. Stand and unfold yourself' (I,i,l-2). Before Francisco yields his watch to the man sent to relieve him, he poses Barnardo's question to new interlopers, calling again into the night, 'Who is there?' (I,i,l4). It is Horatio, come to see the rumoured ghost. When it floats into view moments later, he asks, 'What art thou' (I,i,46)?