"Yes, it's rare, but not in the way you think. The explanation's a bit complex, but try and keep up. Chaos theory says that if a butterfly flaps its wings over China, we end up with a storm over America. Since everything in the world is connected, or at least on speaking terms. So, if you could identify and track down that particular butterfly ... Well, I have, and there it is. The little troublemaker. A wonderfully unique item, which I intend to let go for an equally unique price. Oh, the Collector is going to be so jealous!"

(Wilde and the Collector had a thing going once. It didn't work out. No-one ever thought it would, but you just can't tell some people.)

"The butterfly theory is nothing new, really," said Grave, in her most academic and tweedy voice. Auctioneers always sound like failed scholars. Probably because most of them are. "The ancient Romans had people called Augurs who could predict the future by studying the flight of birds."

Wilde gave her a withering look. "They also had a tendency to cut open goats, then accuse people of treason over which way the goat's liver was pointing. And give themselves lead poisoning with their choice of plumbing materials."

"Let us all make a valiant effort to stick to the point, please," I said. "Isn't the whole butterfly thing just a metaphor? There isn't a real butterfly, as such."

Wilde hit me with her most withering smile. "Metaphors can be as real as anything else in the Night-side, darling. Symbols can have their own identity here. So, whatever lucky person takes possession of this butterfly at auction will possess the power to identify all such butterflies; the first domino in the line that will produce future events. The owner should then be able to predict and possibly even control the way the future turns out. The possibilities are endless! In theory, anyway. Trust me on this, John darling; I am going to be rich, rich, rich!"