Elidee led Billy and me through alleys, up a fire escape to the roof of a building and then down on the other side, and through a junk-cluttered abandoned lot on the way to the Pedway. It took us better than half an hour of scrambling after the tiny faerie through the muggy heat, and by the end of it I wished I'd told Toot-toot that we wanted someone who could read a street map and guide us there in a car.

Chicago's commuter tunnels are fairly recent construction, compared to much of the rest of the city. The tunnels are a maze if you don't know them - long stretches of identical overhead lights, drab, clean walls dotted with advertising posters, and intersections bearing plain and not always helpful directional signs. The tunnels closed after the workday and wouldn't open up again until around six the next morning, but Elidee led us to an unfinished building at Randolph and Wabash. She flitted around in front of a service access door that proved to be unlocked and that led down to a similar door that opened onto a darkened section of the Pedway that looked as though it had been under construction but was abandoned when the building had shut down.

It was completely dark, so I slipped the silver pentacle off my neck, lifting it in my hand and focusing a quiet effort of will upon it. The five-pointed star has been a symbol of magic for centuries, representing the four elements and the power of spirit bound within the circle of will - primal power under the control of human thought. I held the pentacle before me, and as I concentrated it began to glow with a gentle blue light, illuminating enough of our surroundings that we could navigate through the dark, silent tunnels. The little faerie drifted in front of us down the tunnel, and we followed her without speaking. She took us to the intersection with the main tunnels of the Pedway and on a brief walk down another tunnel, to a section shut behind a rusting metal gate with a sign that read, DANGER KEEP OUT. The gate proved to be unlocked, and we went down the tunnel, into a damper section of tunnels, rife with the smell of mold, that was clearly not a part of the Pedway proper.

After another fifty or sixty feet we reached a place where the walls became rough and uneven and shadows lay thick and heavy, despite the glow of my wizard's light.

Elidee drifted over to an especially dark section of wall and flew in a little circle in front of it.

"Okay," I said. "I guess this is where we get in."

"What is where we get in?" Billy asked, his voice skeptical. "Get into where?"

"Undertown," I said. I ran my hands over the wall. To the casual touch it appeared to be bare, unfinished concrete, but I felt a slight unsteadiness when I pressed against it. It couldn't have been solid stone. "Must be a panel here somewhere. Trigger of some kind."

"What do you mean, 'Undertown'? I've never heard of it before."

"I was probably working here for five or six years before I did," I said. "You have to understand the history of Chicago. How they did things here."

Billy folded his arms. "I'm listening."

"The city is a swamp," I said, still searching for a means of opening the door with my fingertips. "We're darn near level with Lake Michigan. When they first built the place, the town kept sinking into the muck. I mean, every year it sank lower. They used to build streets, then build a latticework of wood over them, and then another street on top of that, planning on them slowly sinking. They planned houses the same way. Built the front door on the second floor and called it a 'Chicago entry, so when the house sank, the front door would be at ground level."

"What about when the street sank?"

"Built another one on top of it. So you wound up with a whole city existing under the street level. They used to have a huge problem with rats and criminals holing up under the streets."

"But not anymore?" Billy asked.

"The rats and thugs mostly got crowded out by other things. Became a whole miniature civilization down here. And it was out of sight of the sun, which made it friendly space for all the night-crawling critters around."

"Hence, Undertown," Billy said.

I nodded. "Undertown. There are a lot of tunnels around Chicago. The Manhattan Project was housed in them for a while during World War Two. Did all that atomic bomb research."

"That's cheerful. You come down here a lot?"

I shook my head. "Hell, no. All kinds of nastiness lives down here."

Billy frowned at me. "Like what?"

"Lots of things. Stuff you don't often see on the surface. Things even wizards know almost nothing about. Goblins, spirits of the earth, wyrms, things that have no name. Plus the usual riffraff. Vampires sometimes find lairs down here during the day. Trolls can hide here too. Molds and fungi you don't get in most of the natural world. You name it."

Billy pursed his lips thoughtfully. "So you're taking us into a maze of lightless, rotting, precarious tunnels full of evil faeries and monsters."

I nodded. "Maybe leftover radiation, too."

"God, you're a fun guy, Harry."

"You're the one who wanted in on the action." My fingers found a tiny groove in the wall, and when I pressed against it a small, flat section of stone clicked and retracted. The switch had to have triggered some kind of release, because the section of wall pivoted in the center, turning outward, and forming a door that led into still more dank darkness. "Hah," I said with some satisfaction. "There we go."

Billy pressed forward and tried to step through the door, but I put a hand on his shoulder and stopped him. "Hang on. There are some things you need to know."

Billy frowned, but he stopped, listening.

"These are faeries. We'll probably run into a lot of the Sidhe, their nobles, hanging out with the Winter Lady. That means that they're going to be dangerous and will probably try to entrap you."

"What do you mean, entrap me?" Billy said.

"Bargains," I said. "Deals. They'll try to offer you things, get you to trade one thing for another."

"Why?"

I shook my head. "I don't know. It's in their nature. The concept of debt and obligation is a huge factor in how they behave."

Billy lifted his eyebrows. "That's why that little guy worked for you, right? Because he owed you for the pizza and he had a debt to you."

"Right," I said. "But it can work both ways. If you owe them something, they have a conduit to you and can use magic against you. The basic rule is not to accept any gifts from them - and for God's sake, don't offer them any gifts. They find anything other than an equal exchange to be either enticing or insulting. It isn't a big deal with little guys like Toot, but if you get into it with a Sidhe Lord you might not live through it."

Billy shrugged. "Okay. No gifts. Dangerous faeries. Got it."

"I'm not finished. They aren't going to be offering you wrapped packages, man. These are the Sidhe. They're some of the most beautiful creatures there are. And they'll try to put you off balance and tempt you."

"Tempt me? Like with sex, is that what you're saying?"

"Like any kind of sensual indulgence. Sex, food, beauty, music, perfume. When they offer, don't accept it, or you'll be opening yourself up to a world of hurt."

Billy nodded. "Okay, got it. Let's go already."

I eyed the younger man, and he gave me an impatient look. I shook my head. I don't think I could have adequately conveyed the kind of danger we might be walking into with mere words in any case. I took a deep breath and then nodded to Elidee. "All right, Tinkerbell. Let's go."

The tiny scarlet light gave an irritated bob and then darted through the concealed doorway and into the darkness beyond. Billy narrowed his eyes and followed it, and I went after him. We found ourselves in a tunnel where one wall seemed to be made of ancient, moldering brick and the other of a mixture of rotting wooden beams, loose earth, and winding roots. The tunnel ran on out of the circle of light from my amulet. Our guide drifted forward, and we set out to follow her, walking close together.

The tunnel gave way to a sort of low-roofed cavern, supported here and there by pillars, mounds of collapsed earth, and beams that looked like they'd been added in afterward by the dwellers in Undertown. Elidee circled in place a bit uncertainly, then started floating to the right.

I hadn't been following the little faerie for five seconds before the skin on the back of my neck tried to crawl up over my head and hide in my mouth. I drew up short, and I must have made some kind of noise, because Billy shot a look back at me and asked, "Harry? What is it?"

I lifted a hand to silence him and peered at the darkness around me. "Keep your eyes open," I said. "I don't think we are alone."

From the shadows outside the light came a low hissing sound. The rest of my skin erupted in gooseflesh, and I shook my shield bracelet clear. I lifted my voice and said clearly, "I am the Wizard Dresden, Emissary of the Winter Court, bound to pay a call upon the Winter Lady. I've no time or desire for a fight. Stand clear and let me pass."

A voice - a voice that sounded like a tortured cat might, if some demented being gave it the gift of speech - mewled out of the shadows, grating on my ears. "We know who you are, wizard," the voice said. Its inflections were all wrong, and the tone seemed to come from not far above the ground, somewhere off to my right. Elidee let out a high-pitched shriek of terror and zipped back to me, diving into my hair. I felt the warmth of the light around the tiny faerie like a patch of sunlight on my scalp.

I traded a look with Billy and turned toward the source of the voice. "Who are you?"

"A servant of the Winter Lady," the voice replied from directly behind me. "Sent here to guide you safely through this realm and to her court."

I turned in the other direction and peered more closely toward the sound of the voice. The werelight from my amulet suddenly gleamed off a pair of animal eyes, twenty feet away and a few inches from the floor. I looked back at Billy. He'd already noted the eyes and turned to put his back to mine, watching the darkness behind us.

I turned back to the speaker and said, "I ask again. Who are you?"

The eyes shifted in place, the voice letting out an angry, growling sound. "Many names am I called, and many paths have I trod. Hunter I have been, and watcher, and guide. My Lady sent me to bring you thither, safe and whole and well."

"Don't get mad at me, Charlie," I snapped. "You know the drill as well as I do. Thrice I ask and done. Who are you?"

The voice came out harsh and sullen, barely intelligible. "Grimalkin am I called by the Cold Lady, who bids me guide her mother's Emissary with safe conduct to her court and her throne."

I let out a breath. "All right," I said. "So lead us."

The eyes bobbed in place, as though in a small bow, and Grimalkin mewled again. There was a faint motion in the shadows outside my light, and then a dull greenish glow appeared upon the ground. I stepped toward it and found a faint, luminous footprint upon the ground, a vague paw, feline but too spread out and too thin to be an actual cat's. Just as I reached it, another light appeared on the floor several feet away.

"Make haste, wizard," mewled Grimalkin's voice. "Make haste. The Lady waits. The season passes. Time is short."

I moved toward the second footprint, and as I reached it a third appeared before us, in the dark, and so on.

"What was that all about?" Billy murmured. "Asking it the same thing three times, I mean."

"It's a binding," I murmured in reply. "Faeries aren't allowed to speak a lie, and if a faerie says something three times, it has to make sure that it is true. It's bound to fulfill a promise spoken thrice."

"Ah," Billy said. "So even if this thing hadn't actually been sent to guide us safely, you made him say so three times would mean that he'd be obligated to do it. Got it."

I shook my head. "I wanted to make sure Grimalkin was on the level. But they hate being bound like that."

From ahead of us, the faintly glowing eyes appeared briefly, accompanied by another mewling growl that sent a chill down my spine.

"Oh," Billy said. He didn't look any too calm himself. His face had gone a little pale, and he walked with his hands clenched into fists. "So if Grimalkin had good intentions to begin with, wouldn't that make him angry that you needlessly bound him?"

I shrugged. "I'm not here to make friends, Billy. I'm here to find a killer."

"You've never even heard of diplomacy, have you?"

We followed the trail of footprints on the ground for another twenty minutes or so, through damp tunnels, sometimes only a few feet high. More sections of the tunnel showed evidence of recent construction - if you could call swirling layers of stone that seemed to have been smoothed into place like soft-serve ice cream "construction." We passed several tunnels that seemed entirely new. Whatever beings lived down here, they didn't seem too shy about expanding. "How much further?" I asked.

Grimalkin let out a mrowling sound from somewhere nearby - not in the direction of the next footprint, either. "Very near, noble Emissary. Very near now."

The unseen faerie guide was good to its word. At the next glowing footprint, no other appeared. Instead, we came to a large, elaborately carved double doorway. Made of some black wood I could not identify, the doors were eight or nine feet high, and carved in rich bas-relief. At first I thought the carvings were of a garden theme - leaves, vines, flowers, fruit, that kind of thing. But as I walked closer to the door, I could see more detail in the light of my glowing amulet. The forms of people lay among the vines. Some sprawled amorously together, while others were nothing more than skeletons wrapped in creeping roses or corpses staring with sightless eyes from within a bed of poppies. Here and there in the garden one could see evidence of the Sidhe - a pair of eyes, a veiled figure, and their hangers-on, little faeries like Toot-toot, leaf-clad dryads, pipe-wielding satyrs, and many, many others hiding from the mortals' views, dancing.

"Nice digs," Billy commented. "Is this the place?"

I glanced around for our guide, but I didn't see any more footprints or any feline eyes. "I guess it must be."

"They aren't exactly subtle, are they?"

"Summer's better at it than Winter. But they all can be when it suits them."

"Uh-huh. You know what bothers me, Harry?"

"What?"

"Grimalkin never said he'd guide us out again."

I glanced back at Billy. Quiet, hissing laughter came out of the darkness, directionless. I took a deep breath. Steady, Harry. Don't let the kid see you get nervous. Then I turned to the door and struck it solidly with my fist, three times.

The blows rang out, hollow and booming. Silence fell on the tunnels for a long moment, until the doors split down the middle, and let out from behind them a flood of light and sound and color.

I don't know what I'd expected from the Winter Court, but it wasn't big-band music. A large brass section blared from somewhere behind the doors, and drums rattled and pounded with the rough, genuine sound of actual skins. The lights were colored and muted, as if the whole place was lit by Christmas strands, and I could see shadows whirling and moving inside - dancers.

"Careful," I muttered. "Don't let the music get to you." I stepped up to the great doors and passed through them.

The room could have come from a Roaring Twenties hotel. Hell, it might have been, if the hotel had sunk into the earth, turned slightly upon its side, and been decorated by things with no concept of human values. Whatever it had once been, it had always been meant for dancing. The dance floor was made of blocks of rose-colored marble, and even though the floor was tilted, the blocks had been slipped to the level, here and there, creating something that looked almost like a flight of low, shallow stairs. Over the treacherous blocks danced the Winter Sidhe.

Beautiful didn't come close. It didn't start to come close. Men and women danced together, dressed in regalia of the 1940s. Stockings, knee-length skirts, dress uniforms of both the army and the navy that looked authentic to the month and year. The hairstyles in evidence corresponded as well, though the color didn't always match the setting. One Sidhe girl I saw wore hers dyed sapphire-blue, and others wore braids of silver and gold, or of other colors. Here and there, light gleamed from metal or gems set into ears, brows, or lips, and the riot of subtle colors gathered around each and every dancer in its own distinct, fascinating nimbus, a corona of energy, of power manifesting itself as the Sidhe danced.

Even without the whirling auras, the way they moved was something hypnotic in itself, and I had to force my eyes away from it after only a few seconds of lovely legs being displayed as a woman spun, body arched back underneath a strong man's hands, throats bared and breasts offered out, as hair caught the gleam of the colored lights and threw it back in waves of color. I couldn't look anywhere on the dance floor without seeing someone who should have been making fun of people on the covers of magazines for being too ugly.

Billy hadn't been as paranoid as me, and he stood staring at the dance floor, his eyes wide. I nudged him with my hip, hard enough to make his teeth clack together, and he jerked and gave me a guilty look.

I forced my eyes away from the dancers, maybe twenty couples all told, to check out the rest of the ballroom.

To one side of the room stood a bandstand, and the musicians on it all wore tuxes. They were mortals, human. They looked normal, which was to say almost deformed in comparison to the dancers they performed for. Both men and women played, and none of them looked well rested or well fed. Their tuxes were stained with sweat, their hair hung lank and unwashed, and a closer look showed a silver manacle bound around the ankle of each of them, attached to a chain that ran through the bandstand, winding back and forth among them. They didn't look upset, though - far from it. Every one of them was bent to the music, faces locked in intensity and concentration. And they were good, playing with the unity of tone and timing that you only see from bands who have really honed their art.

That didn't change the fact that they were prisoners of the fae. But they evidently had no particular problems with the notion. The music rattled the great stone room, shaking dust from the ceiling hidden in the darkness overhead while the Sidhe danced.

Opposite the bandstand, the dance floor descended directly into a pool of water - or what I presumed was water, at any rate. It looked black and unnaturally still. Even as I watched, the waters stirred, moved by something out of sight beneath the surface. Color rolled and rippled over the dark surface, and I got the distinct impression that the pool wasn't water. Or not just water. I fought down another shiver.

Beyond the dance floor, on the side of the room opposite me, stood raised tiers of platforms, each one set with a separate little table, one that could sit three or four at the most, each one with its own dim, green-shaded lamp. The tables all stood at different relative heights to one another, staggered back and forth - until the tiers reached a pinnacle, a single chair made out of what looked like silver, its flaring back carved into a sigil, a snowflake the size of a dinner table. The great chair stood empty.

The drummer on the bandstand went into a brief solo, and then the instruments cut off altogether - but for one. The other band members sagged into their seats, a couple of them simply collapsing onto the floor, but the lead trumpet stayed standing, belting out a solo while the Winter Lords danced. He was a middle-aged man, a little overweight, and his face flushed scarlet, then purple as his trumpet rang out through the solo.

Then, all at once, the Sidhe stopped dancing. Dozens of beautiful faces turned to watch the soloist, eyes glittering in the muted light.

The man continued to play, but I could see that something was wrong. The flush of his face deepened even more, and veins began to throb in his forehead and throat. His eyes widened and began to bulge, and he started shaking. A moment later the music began to falter. The man tore his face away from the trumpet, and I could see him gasping for breath. He couldn't get it. A second later he jerked, then stiffened, and his eyes rolled up in his head. The trumpet slipped from his fingers, and he fell, first to his knees and then limply over onto his side, to the floor of the bandstand. He hit with finality, his eyes open but not focused. He twitched once more, and then his throat rattled and he was still.

A murmur went through the Sidhe, and I looked back to see them parting, stepping aside with deep bows and curtseys for someone emerging from their midst. A tall girl walked slowly toward the fallen musician. Her features were pale, radiant, perfect - and looked like an adolescent copy of Mab's. That was where the resemblance ended.

She looked young. Young enough to make a man feel guilty for thinking the wrong thoughts, but old enough to make it difficult not to. Her hair had been bound into long dreadlocks, each of them dyed a different shade, ranging from a deep lavender to pale blues and greens to pure white, so that it almost seemed that her hair had been formed from glacial ice. She wore leather pants of dark, dark blue, laced and open up the outside seams from calf to hip. Her boots matched the pants. She wore a white T-shirt tight enough to show the tips of her breasts straining against the fabric, framing the words OFF WITH HIS HEAD. She had hacked the shirt off at the top of her rib cage, leaving pale flesh exposed, along with a glitter of silver flashing at her navel.

She moved to the downed musician with a liquid grace, a thoughtless, casual sensuality that made a quiver of arousal slip down my spine. She settled down over him, throwing a leg over his hips, straddling him, and idly raked long, opalescent fingernails over his chest. He didn't move. Didn't breathe.

The girl licked her lips, her mouth spreading into a lazy smile, before she leaned down and kissed the corpse's dead lips. I saw her shiver with what was unmistakably pleasure. "There," she murmured. "There, you see? Never let it be said the Lady Maeve does not fulfill her promises. You said you'd die to play that well, poor creature. And now you have."

A collective sigh went up from the assembled Sidhe, and then they began applauding enthusiastically. Maeve looked back over her shoulder at them all with a lifted chin and a lazy smile before she stood up and bowed, left and right, to the sound of applause. The applause died off when Maeve stalked away from the corpse and to the rising tiers of dinner seats, stepping lithely up them until she reached the great silver throne at the top. She dropped into it, turned sideways, and idly threw her legs over one arm, arching her back and stretching with that same lazy smile. "My lords and ladies, let us give our poor musical brutes a little time to recover their strength. We have a visitor."

The Sidhe began drifting toward the tables on the tiers, stepping into place one by one. I stood where I was and said nothing, though as they settled down I became increasingly conscious of their attention, of the glittering intensity of immortal eyes upon me.

Once they were all settled in, I stepped forward and walked across the dance floor until I stood at the foot of the tier. I looked up at Maeve and inclined my head to her. "Lady Winter, I presume."

Maeve smiled at me, showing a dimple, and gave one foot a girlish bounce. "Indeed."

"You know in what capacity I am here, Lady?"

"Naturally."

I nodded. Nothing like a frontal assault, then. "Did you arrange the murder of the Summer Knight?"

Silence fell on the room. The regard of the Winter Sidhe grew more intent, more uncomfortable.

Maeve's mouth spread into a slow smile, which in turn became a quiet, rolling laugh. She let her head fall back with it, and the Sidhe joined in with her. They sat there laughing at me for a good thirty seconds, and I felt my face begin to heat up with irrational embarrassment before Maeve waved one hand in a negligent gesture and the laughter obediently died away.

"Stars," she murmured, "I adore mortals."

I clenched my jaw. "That's swell," I said. "Did you arrange the murder of the Summer Knight?"

"If I had, do you really think I would tell you?"

"You're evading," I growled. "Answer the question."

Maeve lifted a fingertip to her lips as though she needed it to hold in more laughter. Then she smiled and said, "I can't just give you that kind of information, Wizard Dresden. It's too powerful."

"What is that supposed to mean?"

She sat up, crossing her legs with a squeak of leather, and settled back on the throne. "It means that if you want me to answer that question, you're going to have to pay for it. What is the answer worth to you?"

I folded my arms. "I assume you have something in mind. That's why you sent someone to give us safe passage here."

"Quick," she murmured. "I like that. Yes, I do, wizard." She extended a hand to me and gestured to an open seat at the table to the right and a little beneath the level of her throne. "Please sit down," she said. Her teeth shone white. "Let's make a deal."