The knife came out of the reeds before the reeds made a sound. I caught the wrist and felt the blade shiver against my jaw, but he was already lunging, and my feet went out from under me in the black water of the fen. We went down together, knee and elbow, and I drove my knee into his belly until he gave up all the air in his lungs.

"Are you done?" I said.

"Done," he wheezed.

I kept his knife, dragged him onto the hummock where a drowned oak stood like a broken god, and sat him up against the roots. He was a thin man with a wound in his side that had gone bad, and the fever sat in his eyes like a second tenant.

"You're a warden," he said. "Order's coat."

"That's right."

"You hunt the boy."

I put my hand on my chest, where the clay pot rode under my shirt, warm against my heart. I said nothing.

"They say the healer spreads the plague with his touch. Say he's a cup of poison walking through the villages." He laughed, and the laugh cost him. "He healed my sister. Put his palm on her forehead and the phlegm left her in one great haul. That's the plague I caught for him. The Order's truth."

"Where is he?"

"Three nights gone, north." He pointed. "Brother Silas is two days behind with a company of cutters. They take the healed ones and hang them from the ash trees, hands cut off, hung around their necks. The boy knows. He ran."

"They sent the father," he said, and his eyes held the careful pity of a dying man. "Of course they sent the father. Who else can be trusted to cut the root?"

I had heard that before, the Order's way. Everything wears a father's face. I left him my waterskin. I had no friendlier medicine.

The garrison sat on the bones of the old cathedral, a low hall of gray stone where the monks had kept their lamps before the Order renamed God. Commander Ashworth met me in the refectory, where the long tables still carried the carved signs for bread and salt. He was a thin man, knobbed at the shoulders like a tree, and his hands were clean, the way a man's hands are clean when he has never touched a wound.

"The boy?" he said.

"North of the fen. Wounded. Gray."

"And your orders?"

I touched the clay pot over my heart, but I did not say that. "You gave me the vinegar."

"I gave you mercy." Ashworth set a sealed vial on the table between the carved bread and the carved salt. The red wax caught the last light. "The plague is in his breath. The healers call it a cure, but the Lord we serve knows better. When you find him, open his mouth and pour. It will be quick."

"You want a father to poison his son."

"I want a soldier to finish what the sickness began." He looked at me the way the Order looked at everything, as if the whole world were a soul to be saved and every wound a lie that needed closing. "This is not the world we made, Thomas. It is the world that must be endured. The boy was born to be a wound in it. You were born to close him. That is fate, and fate does not ask."

I took the vial. It was cold. It had nothing of the pot in it. The clay pot had been warm for fourteen years, since Edmund was two and burned his arm on the kettle, and my wife Gertrude mixed the sage and honey and poured them over the burn, saying, This will follow him, this will remember him. She died that winter. The pot stayed with the boy until the Order wrote his name in their book, and then I took the pot, and the distance opened between us, one mile and then a hundred, and the old burn went on aching in a pot I carried against my breathing. The distant wound.

At the fen's edge I met Catherine Pemberton. She was old as the drowned oaks and twice as bitter. She stepped out of the dusk with a sack of roots over her shoulder, and she knew my coat before I knew her face.

"Warden Bradshaw," she said. "Or is it father now?"

I stopped.

"The boy is ahead of you," she said. "And Brother Silas ahead of him. They burn the healed ones, you know. Your Order calls the fire a cure."

"I'm not the Order."

"You carry their seal." She looked at my breast, at the pot's outline under the wool. "But that isn't their seal, is it? That's a mother's saying in a pot of clay."

The air of the fen went cold. The mist braided itself around her ankles like the fingers of the buried. The country runs deep in ghost, I thought. Every fenman knows it. And Catherine Pemberton was one of the deep ones.

"What do you need, soldier? Medicine?" She laughed. "I have no medicine can haul a father across the miles."

I told her about the vinegar. I told her about the orders. She was quiet for so long I thought she had gone, and then she put her hand in her sack and held out a tin of black paste that stank of wormwood and gunpowder.

"The boy healed a girl in the village. The Order burned her, but not before she passed the cure to him. He carries the plague in his palms now. The more he heals, the deeper the black climbs his arms. For him to heal, he must spend himself. Don't you see the shape of it? Every soul he saves pays from his own blood." She pushed the tin into my hand. "Hellebore. If the black reaches his heart, no vinegar and no love will matter. That's my medicine. Now let me see yours."

Reluctantly I pulled the clay pot from my shirt. She pried the lid with her thumb. The salve inside had gone dry, flaking, pale as bone. She smelled it, and her mouth turned down.

"That is not salve," she said. "That is grief. It can heal nothing but sorrow, and only if you burn it."

"Gertrude made it for his burn."

"Gertrude is dead, and the boy is dying." She handed the pot back, and her fingers were cold as the fen. "You carried your wife's good-bye for fourteen years. It is the only medicine you own, and it will not cross the distance. Listen to me, Warden. The wound you carry is not your son's arm. It is the distance itself. And distance is not a thing you heal. It is a thing you close with your feet."

I took the hellebore. I did not believe in it. But I kept it.

The fen gave way to broken hill-country, where the plague had barbered the villages and left black crosses at