The last page of Henry James’s Portrait of a Lady (1881) leaves its heroine, Isabel Osmond, with an ambiguous choice. To go back into the cage of her wretched marriage might be an exercise of will for duty’s sake, or an evasion, based on fear. Readers have been disputing Isabel’s motives ever since her creator so provokingly left the door ajar. Now, distinguished Irish novelist John Banville has taken it on himself to answer the question that James left hanging. What will Isabel do next, and why?