It was an axiom of shadow work that the best way to find something hidden was not to look for it directly. Instead, you watched other things that might be affected by the item you were after. You looked for unusual reactions, strange perturbations that were not logical. And when you found the perturbations, the chance was good that what you were actually seeing was the effect your hidden target had on things around it. If you looked in enough areas, cataloged enough perturbations, you could often mentally calculate the exact location of your original subject. Someone had once told Sly that this technique came from astronomy, and was responsible for the discovery of one of the outer planets—Pluto, she thought it was. Astronomers had measured strange perturbations in the orbits of other planets, and postulated that they were caused by the gravity of another, as yet undiscovered, world. They calculated where that new world would have to be to cause the measured effects, pointed their telescopes to that part of the sky, and bingo.