"So what are you after?" Richard asked Hunter. The three of them were walking, with extreme care, along the bank of an underground river. The bank was slippery, a narrow path along dark rock and sharp masonry. Richard watched with respect as the gray water rushed and tumbled, within arm's reach. This was not the kind of river you fell into and got out of again; it was the other kind.
    "After?"
    "Well," he said. "Personally, I'm trying to get back to the real London, and my old life. Door wants to find out who killed her family. What are you after?" They edged along the bank, a step at a time, Hunter in the lead. She said nothing in reply. The river slowed and fed into a small underground lake. They walked beside the water, their lamps reflecting in the black surface, their reflections smudged by the river mist. "So what is it?" asked Richard. He did not expect any kind of answer.
    Hunter's voice was quiet and intense. She did not break her step as she spoke. "I fought in the sewers beneath New York with the great blind white alligator-king. He was thirty feet long, fat from sewage and fierce in battle. And I bested him, and I killed him. His eyes were like huge pearls in the darkness." Her strangely accented voice echoed in the underground, twined in the mist, in the night beneath the Earth.
    "I fought the bear that stalked the city beneath Berlin. He had killed a thousand men, and his claws were stained brown and black from the dried blood of a hundred years, but he fell to me. He whispered words in a human tongue as he died." The mist hung low on the lake. Richard fancied that he could see the creatures she spoke of, white shapes writhing in the vapor.
    "There was a black tiger in the undercity of Calcutta. A man-eater, brilliant and bitter, the size of a small elephant. A tiger is a worthy adversary. I took him with my bare hands." Richard glanced at Door. She was listening to Hunter intently: this was news to her too, then. "And I shall slay the Beast of London. They say his hide bristles with swords and spears and knives stuck in him by those who have tried and failed. His tusks are razors, and his hooves are thunderbolts. I will kill him, or I will die in the attempt."
    Her eyes shone as she spoke of her prey. The river mist had become a thick yellow fog.
    A bell was struck, a little way away, three times, the sound carrying across the water. The world began to lighten. Richard thought he could see the squat shapes of buildings around them. The yellow-green fog became thicker: it tasted of ash, and soot, and the grime of a thousand urban years. It clung to their lamps, muffling the light. "What is this?" he asked.
    "London fog," said Hunter.
    "But they stopped years ago, didn't they? Clean Air Act, smokeless fuels, all that?" Richard found himself remembering the Sherlock Holmes books of his childhood. "What did they call them again?"
    "Pea-soupers," said Door. "London Particulars. Thick yellow river fogs, mixed with coal-smoke and whatever rubbish was going into the air for the last five centuries. Hasn't been one in the Upworld for, oh, forty years now. We get the ghosts of them down here. Mm. Not ghosts. More like echoes." Richard breathed in a strand of the yellow-green fog and began to cough. "That doesn't sound good," said Door.
    "Fog in my throat," said Richard. The ground was becoming stickier, muddier: it sucked at Richard's feet as he walked. "Still," he said, to reassure himself, "a little fog never hurt anyone."
    Door looked up at him with big pixie eyes. "There was one in 1952 that they reckon killed four thousand people."
    "People from here?" he asked. "Under London?"
    "Your people," said Hunter. Richard was willing to believe it. He thought about holding his breath, but the fog was getting thicker. The ground was becoming mushier. "I don't understand," he asked. "Why do you have fogs down here, when we don't have them up there anymore?"
    Door scratched her nose. "There are little pockets of old time in London, where things and places stay the same, like bubbles in amber," she explained. "There's a lot of time in London, and it has to go somewhere--it doesn't all get used up at once."
    "I may still be hung over," sighed Richard. "That almost made sense."

    The abbot had known that this day would bring pilgrims. The knowledge was a part of his dreams; it surrounded him, like the darkness. So the day became one of waiting, which was, he knew, a sin: moments were to be experienced; waiting was a sin against both the time that was still to come and the moments one was currently disregarding. Still, he was waiting. Through each of the day's services, through their scant meals, the abbot was listening intently, waiting for the bell to sound, waiting to know who and how many.
    He found himself hoping for a clean death. The last pilgrim had lasted for almost a year, a gibbering, screaming thing. The abbot regarded his own blindness as neither a blessing nor a curse: it simply _was;_ but even so, he had been grateful he had never been able to see the poor creature's face. Brother Jet, who had cared for the creature, still woke in the night, screaming, with its twisted face before him.
    The bell tolled late in the afternoon, three times. The abbot was in the shrine, on his knees, contemplating their charge. He pulled himself to his feet and made his way to the corridor, where he waited. "Father?" The voice was that of Brother Fuliginous.
    "Who guards the bridge?" the abbot asked him. His voice was surprisingly deep and melodious for such an old man.
    "Sable," came the reply from the darkness. The abbot reached out a hand, grasped the young man's elbow, and walked beside him, slowly, through the corridors of the abbey.

    There was no solid ground; there was no lake. Their feet were splashing through some kind of marsh, in the yellow fog. "This," announced Richard, "is disgusting." It was seeping through his shoes, invading his socks, and making a much closer acquaintance with his toes than Richard was entirely happy with.
    There was a bridge ahead of them, rising up out of the marsh. A figure, dressed in black, waited at the foot of the bridge. He wore the black robes of a Dominican monk. His skin was the dark brown of old mahogany. He was a tall man, and he held a wooden staff as tall as he was. "Hold fast," he called. "Tell me your names, and your stations."
    "I am the Lady Door," said Door. "I am Portico's daughter, of the House of the Arch."
    "I am Hunter. I am her bodyguard."
    "Richard Mayhew," said Richard. "Wet."
    "And you wish to pass?"
    Richard stepped forward. "Yes, we do actually. We're here for a key." The monk said nothing. He lifted his staff and pushed Richard gently in the chest with it. Richard's feet slid out from under him, and he landed in the muddy water. The monk waited a few moments, to see if Richard would swing up and begin to fight. Richard didn't. Hunter did.
    Richard pulled himself up from the mud, and watched, mouth open, as the monk and Hunter fought with quarter-staves. The monk was good. He was bigger than Hunter, and, Richard suspected, stronger. Hunter, on the other hand, was faster than the monk. The wooden staves clacked and whapped in the mist.
    The monk's staff made sudden contact with Hunter's midriff. She stumbled in the mud. He came in close--too close--as he discovered that her stumble had been a feint and her staff slammed into him, hard and precisely, on the backs of his knees, and his legs no longer held his weight. The man tumbled into the wet mud, and Hunter rested the tip of her staff on the back of his neck.
    "Enough," called a voice from the bridge.
    Hunter took a step back. She stood beside Richard and Door once more. She had not even broken a sweat. The big monk got up from the mud. His lip was bleeding. He bowed low to Hunter, then walked to the foot of the bridge.
    "Who are they, Brother Sable?" called the voice.
    "The Lady Door, Lord Portico's daughter, of the House of the Arch; Hunter, her bodyguard, and Richard Mayhew, their companion," said Brother Sable, through bruised lips. "She bested me in fair fight, Brother Fuliginous."
    "Let them come up," said the voice.
    Hunter led the way up the bridge. At the apex of the bridge, another monk was waiting for them: Brother Fuliginous. He was younger and smaller than the first monk they had met, but he was dressed the same way. His skin was a deep, rich brown. There were other black-clad figures, just barely visible, further into the yellow fog. These were the Black Friars, then, Richard realized. The second monk stared at the three of them for a second, and then recited:

    _"I turn my head, and you may go where you want.
    I turn it again, you will stay till you rot.
    I have no face, but I live or die by my crooked teeth--who am I?"_

    Door took a step forward. She licked her lips and half closed her eyes. "I turn my head . . . " she said, puzzling to herself. "Crooked teeth . . . go where you . . . " Then a smile spread over her face. She stared up at Brother Fuliginous. "A key," she said. "The answer is, you're a key."
    "A wise one," acknowledged Brother Fuliginous. "That's two steps taken. One more to take."
    A very old man stepped out of the yellow fog and walked cautiously toward them, his gnarled hand holding onto the stone side of the bridge. He stopped when he reached Brother Fuliginous. His eyes were a glaucous blue-white, thick with cataracts. Richard liked him on sight. "How many of them are there?" he asked the younger man, in a deep and reassuring voice.
    "Three, Father Abbot."
    "And has one of them bested the first gatekeeper?"
    "Yes, Father Abbot."
    "And did one of them answer the second gatekeeper correctly?"
    "Yes, Father Abbot."
    There was regret in the old man's voice. "So, one of them is left to face the Ordeal of the Key. Let him or her stand forward now."
    Door said, "Oh no."
    Hunter said, "Let me take his place. I will face the ordeal."
    Brother Fuliginous shook his head. "We cannot permit that."
    When Richard was a small boy he had been taken, as part of a school trip, to a local castle. With his class he had climbed the many steps to the highest point in the castle, a partly ruined tower. They had clustered together at the top, while the teacher pointed out to them the whole of the countryside, spread out below. Even at that age, Richard had not been very good at heights. He had clutched the safety rail, and closed his eyes, and tried not to look down. The teacher had told them that the drop from the top of the old tower to the bottom of the hill it overlooked was three hundred feet; then she told them that a penny, dropped from the top of the tower, would have enough force to penetrate the skull of a man at the bottom of the hill, that it would crack a skull like a bullet. That night Richard lay in bed, unable to sleep for imagining the penny falling with the power ............