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.