Fidelis Berlin, who has featured in several of my books and plays a large part in the most recent one, Dead Woman Walking, is an old woman. She is in fact about the same age as me, which I admit because there is certainly no point now (if there ever was a point) in pretending otherwise, since the truth can so easily be found on line. I don't know who first remarked that old women are invisible, but rather to my surprise, it seems to be true. For example: last week, in a train on the way from Cornwall to London, the inspector came along the coach scrupulously checking everybody's tickets and rail cards - or rather, I should say checking everyone else's. But his eyes passed unseeingly over my seat. I was invisible. I would have minded being ignored if it hadn't given me an idea. As people say to young journalists, every unpleasant experience can be made into good copy.