Something cold and haughty flickered through Mab's eyes. "Promises must be kept," she murmured, and the words made wave, wind, and stone tremble. "My vassal's oaths and bargains are binding upon me, so long as I restrain her from fulfilling them."

"Does that mean that you will help me?" I asked.

"It means that I will give you what she might give you," Mab said, "and speak what knowledge she might have spoken to you were she here in flesh, rather than in proxy." She tilted her head slowly to one side. "You know, wizard, that I may speak no word that is untrue. Thus is my word given to you."

I eyed her warily. It was true that the high Sidhe could not speak words that were untrue—but that wasn't the same thing as telling the truth. Most of the Sidhe I had met were past masters of the art of deception, speaking in allusions and riddles and inferences that would undermine the necessary honesty of their words so thoroughly that they might be much stronger lies than if they had simply spoken a direct falsehood. Trusting the word of one of the Sidhe was an enterprise best undertaken with extraordinary caution and exacting care. If I had any choice in the matter, I would avoid it.

But there was nothing I could do but forge ahead. I still had to find out more about what Sergeant Kemmler's Lonely Hearts Club Band was doing in Chicago, and that meant taking the risk of speaking with my godmother. Mab was simply more of the same risk.

A lot more of it.

"I seek knowledge," I said, "about the one known as the Erlking."

Mab arched an eyebrow. " Him," she said. "Yes. Your godmother knows some little of him. What would you know of him?"

"I want to know why all of Kemmler's disciples are grabbing up all the copies of the White Council's book about him."

Nothing that I could imagine would truly rattle Mab's composure, but that sentence apparently came close. Her expression froze, and with it the wind came to a sudden, dead halt. The waves of the shore abruptly stilled to a sheet of glass beneath her feet, dimly reflecting the glow of the city skyline in the distance and the last shreds of purple light in the leaden sky.

"Kemmler's disciples," she said. Her eyes were deeper than the lake she stood upon. "Could it be?"

"Could what be?" I asked.

"The Word," she said. " The Word of Kemmler. Has it been found?"

"Um," I said. "Sort of."

Her delicate white brows rose. "Meaning what, pray tell?"

"Meaning that the book was found," I said. "By a local thief. He tried to sell it to a man named Grevane."

"Kemmler's first student," Mab said. "Did he acquire the book?"

"No," I said. "The thief used mortal technology to conceal the book, in order to prevent Grevane from taking it from him without paying."