Our identity, our self-image, is built up through our childhood, our youth, into a mosaic of all we have learned about the world, about ourselves and our position in it. But what if a key part part of that information suddenly turns out to be false? What if, for instance, one of our parents turns out not to be the person we thought they were, but someone else altogether? I always thought that my father was a Canadian, of Irish descent. But in my middle age, long after he had been taken from the world by a car accident, and after my mother had died, I made the astonishing discovery that he was...