"We thought it... it might be a spell," Yaotl said. "That you'd help."

"I'm a priest for the Dead," I told him gently, smoothing the hair on the boy's forehead. "The only magic I have is to usher the souls of the dead into the underworld." And other things, too, most notably making sure that nothing of the underworld came back among us. "Why bring him here, rather than to the Great Temple?"

Yaotl shook his head. "The priests at the Great Temple are too obsessed with their sacrifices. They don't care about human lives."

Human lives, as I knew all too well from numerous funeral wakes, were worth nothing. Death was cheap, and caught us all, often giving little warning as to its coming. But this a the purplish, clenched lips, the pale face, the shaking fingers a this wasn't a death I'd have wished on anyone, much less a child. "How long has he been like this?" I asked.

"One week," Yaotl said. "Chimalli woke up one morning and refused to get up. He said that he was cold. We thought he'd caught a sickness at first. The doctor at the marketplace prescribed sweat baths, but they didn't help. He wouldn't eat, wouldn't leave his sleeping mat. He just... dwindled away."

The boy Chimalli's head came up, the eyes suddenly trained on me with a disturbing intensity. "Leave me alone," he whispered, and his voice echoed as though in a great room.

I shivered. Beside me, Yaotl had gone pale, his face showing a sickly fear unbecoming a warrior, but I didn't blame him. Even during my long career banishing underworld monsters I had seldom seen a gaze so... wrong. Living, and yet stripped of human feelings.

Chimalli's eyes had closed again. I moved cautiously away from him, not eager to repeat the experience. "I'll tell you what I see," I said to Yaotl. "He has the aura of the underworld, though he's still alive."

"Dying, then," Yaotl said curtly. Not a muscle in his face moved. A true warrior to the end.

"No," I said. "The dying don't have this aura. I think he's somehow cursed." I was about to say that I could do nothing to help, when my gaze rested on Chimalli. Four years old. He had outgrown most of the diseases that took their toll on babies and toddlers. His life should have been ahead of him, and yet... "Can you take me to where he sleeps?"

Yaotl nodded. His face still bore no expression, but there was something else, a glimmer in his eyes. I thought it might be hope.

Unsure of what I would find, I armed myself before I left: two obsidian knives went into my belt. I also took a jade and turquoise pectoral of Quetzatcoatl, the Feathered Serpent god, He who had once descended into the underworld to save mankind. It was poor protection against a curse, but without living blood I would not be able to do more.

Yaotl did not speak as we left my temple and headed towards his house. He held Chimalli's hand: the boy followed where he was pulled, but appeared to have no will of his own, like a sacrificial victim drunk on peyotl and led towards the bloody altar.

This, if anything, was creepier than the rest a a wrongness that gave pause even to the passersby.

At this early hour in the afternoon, the streets of Coyoacan were full of people, from peasants in loincloths to priests in tunics and rich cloaks, their hair matted with dried blood.

As we walked, I tried to think on what or whom might have cursed Chimalli. He was young and vulnerable: a target for many monsters, whether supernatural or human.

Beasts of shadows, fierce hunters from the eighth level of the underworld, feasted on human hearts, and would have found Chimalli's lifeforce a rare delicacy. Ciuapipiltin, the Haunting Mothers, preyed on the children they could no longer have a for they were the spirits of mothers dead in childbirth, transformed after death into something darker.

But neither of them fitted. Anything from the underworld would have killed Chimalli outright, not bothering with this slow attrition.

Which left the living. Sorcerers, those who made magic, not with the living blood, but with corpses: the skin of drowned men, the hands of warriors fallen in battle, the finger-nails of strangled captives. Chimalli was too young to have incurred anyone's hatred. However, sorcerers had no scruples, and the child was the perfect vehicle to strike back at Yaotl.

"Do you have any enemies?" I asked Yaotl.

He had been walking in silence; now he turned to me, startled. I guess he had not thought of the possibility, but he did not look wholly surprised. "I'm a warrior, and honoured for my skill on the battlefield. But my father was a peasant, and so was his father before him. Some have no taste for this."

"I see," I said, and waited for something more. But Yaotl's eyes had moved back to his son, and he did not speak again.

Sorcerers needed to be close to their victims to cast their spells. Perhaps there would be some traces near Chimalli's sleeping mat, something to help me track the curse to its source.

I hoped so. For otherwise it was likely that we would never find the culprit. And then Chimalli would die, slowly leeched of life until every part of him belonged to the underworld.

Yaotl's house was in the richer districts, close to the governor's palace. It was a two-storey dwelling, decorated on the outside with numerous frescoes of gods battling our enemies and presiding over sacrifices a the vibrant colours bearing the telltale sheen of new paint.

Inside, a courtyard garden with pine trees and marigold flowers, tended to by slaves, told me that I had not been wrong in my assessment: Yaotl was wealthy, immensely so.

A woman was waiting for us on the doorstep of the private quarters. She was middle-aged, older than Yaotl, but still beautiful, an arresting, stern beauty that time had not yet altered.

Her eyes moved to Chimalli, eagerly searching the boy's blank face, but after a while she stared at Yaotl instead. He in turn shook his head, almost imperceptibly.

Her disappointment was palpable, though she obviously struggled to hide it. "Who is this, Yaotl?" she asked.

I bowed to her, low. "My Lady. I'm Acatl, a priest for the Dead."

Her lips twisted upwards, in what might have been a smile. But there was genuine tenderness in her eyes as she embraced Yaotl. And yet... and yet something was not quite right in their gestures or mumbled words of love; something lay between them, as dark as the blade of an obsidian knife.

"Acatl, meet Xoco, my wife," Yaotl said.

"I'm honoured," I said. Xoco bowed in turn, but said nothing.