I've just had an hour's chat with WNA (see below), and the crime idea has gone out of the window. For good. Lovely Graham at the police station will be terribly disappointed, as he was coming to see it as a joint venture, but I'll give him a signed copy of something (Graham collects signed copies) and hope he understands.
But - having an agent is WONDERFUL! A whole hour just to talk about my ideas, my book, and (even better) her ideas, without feeling I was taking up too much of her time; a whole new experience. (Which is not to say that Will isn't hugely helpful - he is - but this is different).
So it's back to square one, although I may recycle some of my characters. Square one and I are getting rather used to each other, although we have an uneasy relationship, but that can't be helped. Please wish me luck!