"Are we there yet?" said Madman.

"Shut up," I said.

"Are we even still under the Nightside?" said Sinner. "We do seem to have travelled rather a long way."

"We haven't left the Nightside, sweetie," Pretty Poison assured him. "I'd know."

"We are in the dark places of the earth," said Madman. "Where all the ancient and most dangerous secrets are kept. There are Old Things down here, sleeping all around us, in the earth and in the living rock, and in the spaces between spaces. Keep your voices down. Some of these old creatures sleep but lightly, and even their dreams can have force and substance in our limited world. We have come among forgotten gods and sleeping devils, from the days before the world settled down and declared itself sane."

"I think I liked it better when you made no sense at all," said Sinner.

The hovering lights turned out to be paper lanterns, nailed to the rock face at regular intervals. Their tightly stretched sides were made up of silently screaming faces. The eyes in the agonised faces turned to watch us as we passed.

"Are they still alive?" I said. "Still suffering?"

"Oh yes," said Pretty Poison, her voice heavy with a certain satisfaction.

"Hush," said Sinner.

"But what are they?" I said. "Who were they?"

"Uninvited guests," said Madman, and after that no-one felt like talking for a while.

We descended further and further into the earth. The stairs wound around the curving wall of the vast abyss. The dark rock of the wall showed clear signs of having been worked on long ago, at first by tools but later by what seemed to be bare hands. Someone had fashioned this great gulf under the Nightside for a purpose, but who and why and when remained a mystery. Could men have done this, alone or with help? Why would they have wanted to? Was the Lord of Thorns really so dangerous that they had to bury him this deep in the earth? The deeper I went, the more scared I became. My hands were trembling, and my mouth was dry. This was all getting too big, too important for me. I wanted to go back to being just another private investigator, dazzling the natives with tricks and mind games, trading on a reputation I'd never really earned. But I had to go on. I'd come this far for the truth, and though I'd run out of courage and good sense, stubbornness kept me going.

The wall at my shoulder became increasingly pitted and corroded, and thin streams of liquid trickled down the dark stone. I stopped and studied the wet surface closely.

"Don't touch it," said Sinner.

"I wasn't going to. What do you suppose this is? Acid rain, or the underground equivalent?"

"No," said Pretty Poison. "Tears."

Sinner looked at her dubiously. "You know this place?"

"Of it. All demons and angels are warned about this place. We are almost at the domain of the Lord of Thorns, the Overseer of the Nightside."