I emerged through a low doorway behind Thomas onto a platform perhaps twelve feet wide, enclosed by eight crenellated walls the height of a man's chest. Beyond them I could see the carriage drive and the cart track by which I had approached the house, the woods that bordered the path spread out far below us like a green canopy, and behind them, the line of distant blue hills, still misted in the early light. At this height, more than a hundred feet above the ground, the wind was shrill in my ears, slicing across the roof of the tower. On the far side, Jerome once again held Sophia at the point of his knife, his hair whipping over his face. He beckoned to Thomas with his eyes.

"Come, then, Thomas," he called, "will you save her?"

Thomas hesitated a moment and I saw his body stiffen as he gathered his resolve, perhaps trying to judge how quickly he could move compared to Jerome. Sophia whimpered softly, her eyes flicking wildly from Thomas, to me, to the man whose arms now held her close, not for the first time, but now with very different intent. From the confusion and terror in her expression I could tell that she did not know if Jerome was serious or playacting to trap Thomas. I reached out a hand to restrain Thomas, but in that moment he made up his mind and threw himself once again at his former master, bending to hurl his full weight at Jerome's midriff. The priest, pushing Sophia roughly to the ground, tried to stick Thomas with his knife, but Thomas twisted aside at the crucial moment, grabbing Jerome's raised arm in midair. For a moment their arms were raised aloft in the shape of an arch, locked together and trembling with the force of their opposing efforts, the knife flashing silver as it twisted in the air. Then Thomas jerked a knee sharply upward into Jerome's groin; the priest yelped and doubled over, the tension in his arm momentarily lost, and in that second's lapse Thomas bit him hard on the wrist, causing him to drop the knife. But before Thomas could pick it up, Jerome had grasped him by the hair, yanked his head back, and punched him hard in the face. Thomas attempted to hit back, blood coursing down his nose, but Jerome caught him again with a fist hard in the jaw and Thomas stumbled backward, dangerously close to the parapet.

Sophia had wriggled away to the shelter of the wall. I crouched beside her and motioned to the stairway, but she shook her head, her eyes glassy with fear and still riveted on the life-or-death struggle before us. Slowly, so as not to attract attention, I reached out and scrabbled Jerome's fallen knife toward my hand, keeping my eyes on the fighting pair all the time. Thomas, now badly bruised and bleeding, mustered one last burst of energy and thrust a hand forward to grip Jerome by the throat; Jerome, his face contorted with rage, let go of Thomas's hair and clamped both his hands around the boy's neck. They swayed together in this oddly intimate dance, matching each other's steps, now one pushing forward, now the other, both choking and gasping through gritted teeth until it seemed that both must expire in the same moment, so fierce and determined were their crimson faces, when Jerome, who had the advantage of weight and strength, managed to force Thomas a few steps farther back, into a gap between the battlements. Thomas felt the wall against his back and appeared to tighten his hold on Jerome's neck; Jerome leaned all his weight forward, pushing Thomas so that he was hanging backward through the gap, and for a moment I thought they would fall to their deaths together, when suddenly Sophia leaped to her feet, grabbed Jerome's knife from my hand before I realised what she was doing, and ran across to the fighting pair where she stabbed the knife, just once, into Thomas's right hand, still clamped fast around Jerome's throat.

Thomas cried out and released his grip involuntarily; in the same moment Jerome also let go of Thomas's throat and, bracing himself against the brick parapet, gave Thomas one almighty shove in the chest. With a harrowing scream, the boy flailed for a moment, his hands grasping furiously at nothing, before he toppled backward and vanished from our sight, that terrible last cry echoing fainter and fainter as he fell seven tiers to the waiting ground. The impact was so dull that we barely heard it from the roof. I wanted to lean over and look but kept my distance from the parapet, afraid to turn my back to Jerome. Sophia collapsed into his arms, sobbing and shaking violently. Gently he prised the knife from her fingers and rested his chin on the top of her head, breathing hard in ragged gasps. He looked across at me, the fury drained from his face and in its place only a bone-deep exhaustion. He rubbed his throat and twisted his neck from side to side as if to ease the pain.

"It had to come sooner or later," he croaked, his voice barely audible. "He would have been found out eventually, and then he would have taken me down with him."

"We have killed him," Sophia sobbed, raising her tear-streaked face from Jerome's shoulder. "Oh, God, we have killed him! Poor Thomas-he was my only friend once. Will God ever forgive us his blood?" She looked up to the sky, now streaked with bands of blue, the worst of the rain clouds scurrying away toward the horizon.

"He killed two men, Sophia," Jerome said hoarsely, still rubbing his throat. "He would have killed me. We are fighting a holy war, remember. To kill those who oppose God's kingdom is not murder."

"Is that what they teach you at Rheims?" I asked, recovering myself and moving toward the stairs. Now that Jerome was in possession of his knife again I realised how vulnerable I was. I fervently did not want to follow Thomas over the parapet, but it was clear that Sophia could not be counted upon to act against Jerome, and I could not see that there was any chance he might let me walk free.

"And what of Sophia?" I added. "Would it have been murder to have her killed before she reached France? Is she in the way of God's kingdom?"

Jerome laughed abruptly, wincing as the effort hurt his bruised throat.

"You saw for yourself how troubled that boy's mind was, Doctor Bruno. Once he had dirtied his hands with murder, he began to believe the rest of the world was also bent on killing. He was deluded to the very end."

He took a step toward me, but before I could reach the stairs I collided with a body; whipping around, I saw that the doorway was blocked by two solid-looking servants in household livery. One of them, a burly man who was a good foot taller than me, grasped my arm and twisted it up behind my back, sending bursts of white-hot pain through my shoulder. This time I offered no resistance. I was not going to fight my way out of this, I realised. It seemed that unless the Jesuit was willing to show mercy, I had very little hope.

I will ask you again, Bruno-who else knows you are here?" Jerome circled me, his eyes infinitely patient.

"No one," I said through clenched teeth.

"Where are the papers you took from my chamber? The ones Thomas left for you to find?"

I shook my head. "I hid them in my room. No one else knows they are there."

He frowned.

"He is lying," he said, after a pause, addressing the servants. "Listen-we have not much time. You"-he motioned to the second man-"go now, tell Lady Eleanor to expect a visit from the pursuivants in the near future, and request her to send a fast rider to Rowland Jenkes of Catte Street in Oxford. Bring him here as soon as possible. I must get Sophia safely on the road-her father will have people looking for her by now. Then I must return to Oxford. This man"-he nodded toward me-"must be kept alive until Jenkes arrives. He travels with the royal party-there must be nothing in his death that could point to us, any of us. It must be made to look like a highway robbery or some such. But Jenkes must speak to him first. He will be glad to be reunited with you, will he not, Doctor Bruno?"