I peered at the skull. If I didn't know any better, I would think that Bob sounded … nervous? Was that even possible? Bob wasn't a human being. He was a spirit, a being of the Nevernever. The skull was his habitat, his home away from home. I let him stay in it, protected him, and bought him trashy romance novels on occasion in exchange for his help, his prodigious memory, and his affinity for the laws of magic. Bob was a records computer and personal assistant all rolled into one, provided you could keep his mind on the issue at hand. He knew thousands of beings in the Nevernever, hundreds of spell recipes, scores of formulae for potions and enchantments and magical constructions.

No spirit could have that kind of knowledge without it translating into considerable power. So why was he acting so scared?

"Bob, I don't know why you're so upset, but we need to stop wasting time. Sundown's coming in a few hours, and this thing is going to be able to cross over from the Nevernever and hurt someone else. I need to know what it is, and where it might be going, and how to kick its ass."

"You humans," Bob said. "You're never satisfied. You always want to find out what's behind the next hill, open the next box. Harry, you've got to learn when you know too much."

I stared up at him for a moment, then shook my head. "We'll start with basics and work our way through this step by step."

"Dammit, Harry."

"Ghosts," I said. "Ghosts are beings that live in the spirit world. They're impressions left by a personality at the moment of death. They aren't like people, or sentient spirits like you. They don't change, they don't grow-they're just there , experiencing whatever it is they were feeling when they died. Like poor Agatha Hagglethorn. She was loopy."

The skull turned its eye sockets away from me and said nothing.

"So, they're spirit-beings. Usually, they aren't visible, but they can make a body out of ectoplasm and manifest in the real world when they want to, if they're strong enough. And sometimes, they can just barely have any physical existence at all-just kind of exist as a cold spot, or a breath of wind, or maybe a sound. Right?"

"Give it up, Harry," Bob said. "I'm not talking."

"They can do all kinds of things. They can throw things around and stack furniture. There have been documented incidents of ghosts blotting out the sun for a while, causing minor earthquakes, all sorts of stuff-but it isn't ever random. There's always some purpose to it, something related to their deaths."

Bob quivered, about to add something, but clacked his bony teeth shut again. I ginned at him. It was a puzzle. No spirit of intellect could resist a puzzle.