She did not confront him on the path.

She would think, afterwards, that it was the most disciplined thing she had ever done, harder than any assay, harder than a hundred hours at a mass spectrometer. She stood on the gravel with the wind in her hair and the bright morning going on around her, with a crow flying in the pines and the sea washing against the cliffs, and she said, in a voice that was almost level, "I'd like to go in."

"Sienna."

"Not now." She did not look at him. "Tonight. I'll find you in the library after dinner. I'd like to be the one who asks."

There was a pause. She could feel him behind her, and the weight of what he had just done, silent and enormous, like a tree that has begun to fall.

"Yes," Matteo said. His voice was hoarse. "Of course."

She walked back to the house alone, and went up to her room, and shot the bolt, and sat on the edge of the bed with her hands pressed between her knees until the shaking stopped. Then she took out the Divergence Log and wrote nothing at all.

Dinner was served at eight, in a small breakfast room off the kitchen, at a table meant for four. Mrs. Venn brought it herself. Sienna tested every dish, because she could not have stopped herself, and ate nothing. Matteo did not come down. A place was laid for him, and it stayed laid, the silver gleaming, the napkin folded, until Mrs. Venn removed it without a word at half past nine.

The library was on the ground floor at the back of the house, and it was the only room she had not yet explored.

She let herself in at ten. It was a long, high, shadowy room, lined from floor to ceiling with leather-bound books and lit by a single green-shaded lamp on a desk at the far end. A ladder on a brass rail leaned against the shelves. A tall window looked out on the dark garden, and the curtains were drawn half back, so that the glass held two reflections: the lamp, and a man standing in front of it.

He had been waiting for her. She could tell. He had taken off his coat and jacket, and stood in his shirtsleeves with his back to the room, one hand resting on the cold glass. His shoulders were rigid. At the sound of the door he turned, slowly, and she saw his face by lamplight, drawn and gray and without defense.

On the far wall, to the left of the window, stood a glass-fronted cabinet. The blue leather box lay inside on a shelf, closed. She looked at it. Then she looked at him.

"Tell me how you knew," said Sienna.

He did not pretend. He did not ask what she meant. He stood with his hand at his side and his eyes on her face, and something in him that had been held for a very long time gave way, quietly, like a beam that has carried too much.

"May I ask you one thing first?" he said.

"No."

"Then I'll ask it anyway." His voice was very low. "How did you know to test the champagne?"

The lamp hissed softly. In the black window, their two reflections stood facing each other across the length of the room.

She had prepared for everything but this. She had braced for a denial, for a smooth, clever, plausible lie. She had even braced, a little, for a laugh. She had not thought that he would turn the question around, gently, as a man turns a key in a lock he has been trying for a year, and ask it of her.

She said, "I didn't."

"I think you did."

"I didn't test it. That's the whole point. That's the one night in my life I didn't." Her voice cracked on the last word, and she hated it. "I didn't test the champagne. I lifted the glass. I drank. And you stood there with your own glass in your hand and told me not to be afraid."

The silence that followed was so complete that she heard the lamp's wire tick.

Matteo closed his eyes.

It was only a man letting his eyelids fall, very slowly, as if the light had suddenly become unbearable. When he opened them again they were wet. He did not wipe them. He stood where he was, and said, in a voice she hardly recognized, "You remember."

"Yes."

"All of it."

"The cold in my fingers. The coin on my tongue. Your hand on my throat." She heard herself say it, flat and quiet, like a lab report. "The way you lay down beside me on the floor."

He made a low, broken, helpless sound, the sound of a man who has been standing under a very great weight for a very long time and has just felt it lift. He put his hand over his mouth. His shoulders shook once, hard, and then he mastered it, and let the hand fall.

"I thought," he said, and stopped. He tried again. "I've spent a year thinking that I was the only one. That I was losing my mind. That I would put a ring on your finger and watch you fall asleep in a locked room and never be able to tell you why. And you were walking about this house all the while with the same thing inside your head, testing my tea." A shaky, astonished breath that was almost a laugh. "God. Sienna."

She should have felt relief. She had imagined it, in the long nights, this moment: the other person in the room who knew. She had expected it to feel like a hand reaching down. Instead, with a slow, cold, merciless certainty, a different thing was rising in her chest, and it was not relief.

"You were in the room," she said.

He went still.

"You were in the room. It was you who poured. It was you who said a very long life, and meant it, and handed me the glass." She heard her own voice climb. "You knew about the card. You read it, and you hid it, and you went quiet, and then you gave me the flute with your own hand. And two minutes later I was dying on your carpet. So you will forgive me if I do not find this a happy reunion."

"I poured it," Matteo said.

The words dropped into the room like stones into a well.

"I poured it. I did not know." He did not look away. "I have had a year to say that sentence to myself in the mirror, and it has not become any less terrible. I took the bottle out of the ice. I did not test it, because I am a man who has never in his life been afraid of a bottle of wine. I filled both glasses. I put one into your hand. I wished you a long life." His voice broke. "I would have given anything. I would have given every ship in that harbor."

"Then why should I believe you?"

"Because I drank too."

She stared.

"I drank mine. A second after you. I stood there, and I watched you go pale, and I thought: she's ill. It was another full second before I felt it in my own hands. The cold. The taste." He pressed his thumb and forefinger against his eyelids. "You asked, in the lab, what the worst drink at a wedding was. I answered you without thinking. It is the one you don't think to test because someone has been kind. I have been that man. I know exactly how it feels."

The lamp burned steadily. A log shifted in the grate. She stood in the middle of the carpet with her hands clenched at her sides, and her heart hammered so hard that she could taste it.

"The card," she said.

He lowered his hand.

"What did it say?"

"It said, Drink to a long life." His mouth twisted. "That's all. Five words. Written in a slanting, upright hand, in black ink, on thick cream paper." He drew a slow breath. "It was my father's handwriting."

She did not understand at first. Then she did, and the floor seemed to shift beneath her.

"Your father is dead," she said.

"Nine years."

"Then it was a forgery."

"I thought so. In that room, with the card in my hand and you laughing at something I had said, I thought: someone is playing a joke. A cruel, clumsy joke. I put it in my pocket to deal with in the morning." His eyes were dark and haunted. "I did not suspect that it was a message, because I did not yet understand that it was a signature. Someone who knew my father's hand that well. Someone who knew I would hesitate at the sight of it." A pause. "There are very few people alive who could have written it."

"Who?"

"I don't know." He said it clearly, without evasion. "I swear it to you. I have a list, a very short list, and I cannot make any name on it fit. I've had a year, and I have not found the lock."

She looked at him for a long moment. The old animal in her spine said what it always said, which was: this is exactly the sort of thing a clever man would say. It was a great deal quieter than it had been. She found, to her dismay, that she was listening to it with only half an ear.

"Sit down," she said abruptly. "Please. You look as though you might fall."

He did. He sank into the leather chair beside the desk, like a man whose strings had been cut, and leaned his head back and shut his eyes. She did not sit. She went to the cabinet instead, and stood before the glass with her arms folded, looking at the blue box. It seemed a very small thing to hold so much.

"I need to tell you something," she said, to the glass. "About the flutes."

He opened his eyes.

She told him. She stood with her back to him and told it plainly, in order, the way she would have presented a case. The eleven samples, the empty columns, the faint, patient peak far to the left of the trace. The harmless compound sleeping in the etched band of leaves. The acid in the champagne, and how the two of them had met in the glass, in her hand, in the span of a sip. The bottle was innocent. The wine was innocent. The poison had been made at the last, in the mouth of whoever drank.

When she finished, she turned. He had sat up. He was staring at her with an expression she could not read, shock and pain and something close to awe.

"You found that," he said. "In four days. With a mass spectrometer that had only just been repaired."

"I had a good motive."

"I know." A long, unsteady breath. "I know. And I have been sitting in this house for a year with that crystal in a cabinet and it never once crossed my mind that it could be the glass." His hands tightened on the arms of the chair. "You have no idea what you have given me."

"I've given you a method," Sienna said. "I haven't given you a name."

"It will do for a start."

She came away from the cabinet. She did not go near him. She stopped at the edge of the lamplight, with the desk between them, and set her hands flat on the leather blotter.

"When?" she said. "When did you wake up?"

He was silent for a moment. His voice, when it came, was low and strange.

"Two years before the wedding," he said. "Two years before the night. I was at my desk on the ninth floor, signing a ledger, on a Tuesday afternoon in an ordinary week. The sun was in my eyes. And I looked down at the page, and there was a name on it. Hale, Edmund. Debtor. Underneath it, in the margin, in a clerk's hand: daughter, Sienna, toxicology technician, Marenna General. Unmarried." His mouth moved. "I didn't know why. I had not read that name in my life, and I knew it as I knew my own. I sat there for a quarter of an hour with the pen in my hand. Then I looked at the calendar, and it was the wrong year."

The room waited.

"I woke up on the day I first heard yours," Sienna said slowly. She had not known she would say it until it was out. "A year ago. In the lab. The telephone rang at a quarter to eight, and my father said the word Bellandi, and I thought, I know that name, and then I..." She stopped. "Not at the call. Before it. That morning."

"The day we first learned each other's names," said Matteo.

"Yes."

"I did not understand it either. I have never understood it. It has no reason." He rubbed his face with both hands. "But I think that is the rule, if there is one. We went back to the first day the other existed. For me, that was twenty-four months before the poison. For you, only twelve."

"That's why you had a year's start."

"It is why I had a year to be afraid," he said, and the plainness of it undid something in her chest.

She sat down at last. She did it carefully, on the edge of the chair on the far side of the desk, with her hands in her lap. The lamplight lay across the blotter between them, and neither of them touched it.

"The ring," she said.

"I ordered it eleven months ago. From the same jeweler. The same size." He looked at her left hand. "I had held your hand for what I thought was the last time. I remembered it."

"The room."

"I had it stripped in March. I did not want you ever to walk into the room where it happened and find it as it was." His voice was almost inaudible. "I took the sideboard out myself."

"The salt."

He was silent for a long moment. When he spoke, his voice had a quality she had not heard before, a sort of exhausted, helpless honesty.

"I lied about the salt," Matteo said. "I said a technician mentioned it. There was no technician. You did it that morning in the kitchen, at six, on the day we were married, when you thought no one in the house was awake. You stirred a pinch of salt into your coffee at the long table, and you smiled at the cup. I was on the back stairs." He swallowed. "It is the last ordinary thing I remember. I thought: I would like to see her do that again."

She put her hand over her mouth.

It was so small. It was the smallest thing in the world, and it undid her more completely than the champagne, the hand, the terrible carpet. She sat in the green lamplight with her eyes burning and could not speak, and across the desk he looked at her with the same raw, dazed tenderness she had seen in a registry office, and he did not say another word.

At last, when she could trust herself, she said, in a voice she did not recognize, "Davit Orsini."

His face changed.

"The Santa Ilaria. The foreman. The ditch." She forced the words out one at a time. "Did you know?"

"No." It came out very low. "It did not happen the last time. Not any of it. I did not know there was a ship called the Santa Ilaria until the morning it was robbed." His hands had closed into fists. "I have changed things. I did not mean to. I only meant to make a room safe, and a marriage, and a ring. But ripples do not ask which way they are going." He looked at her. "A boy of twenty-three is dead because of something I did, or something someone else did because of what I did, and I do not know which. I do not know where it ends."

"The memory gets less useful," she said slowly.

"Every day."

She saw it then, the shape of it, the great black machinery of cause and consequence turning above them both, and a chill ran down her arms. It was a year in which every step they took would bring them a little further from the ground they knew. The map in their heads was growing old. Soon it would be wrong.

She drew a long breath. She thought of her father in the kitchen, with his hand over hers on the oilcloth. She thought of the plain gold ring on her finger, and a man on a rotting pier, saying: I'd rather hear it from you than guess. She thought of a pale, steady, unreadable face at the head of a long table, and a hand that shook after it had closed a man's life with two fingers.

She thought: sixty-five percent.

And she knew, with the clarity of long practice, that she could no longer tell what that number meant.

"I have conditions," she said.

"Name them."

"We work together. We find who did this, and we stop him, or her, before the fourteenth of September." Her voice steadied as she spoke. "We tell each other everything that bears on the other's safety. Clause seven, in full. No half-truths. No careful sentences."

"Agreed."

"If I ask you a question, you answer it, or you say plainly that you cannot. You don't say not before this year."

A faint, rueful flinch crossed his face. "I deserved that."

"You did." She held his gaze. "And you don't decide for me what I can bear to know. Ever. That's the last one, and it's not negotiable."

He was quiet for a long moment. Then he rose from the chair, slowly, and came around the end of the desk. He stopped a careful two paces from her. He did not touch her. He held out his right hand, palm up, empty, in the old, formal gesture of a man offering an oath.

"On my life," he said, "and on yours."

She took it.

It was a plain handshake, firm and brief, her fingers in his. His palm was warm and dry. It did not tremble. For a moment, only a moment, he held on a fraction longer than a bargain required, and she felt the quick hard pulse at his wrist against her thumb. Then he let go, and stepped back, and the lamp went on burning as if nothing had changed.

Everything had changed.

She stood, and so did he. The clock on the mantel struck midnight, twelve slow strokes. In the dark glass of the window their two reflections stood close together now, not touching, a man and a woman in a lamplit room, and she thought: we died in the house of this man's family, and we are still in it, and both of us are alive.

"Is there anything else?" Sienna said quietly. "Anything about my safety that you haven't told me?"

It was a plain question. She asked it in a plain voice, looking him in the eye, and she saw it land.

It was the smallest of hesitations. A pulse. A breath that began and did not quite finish. His eyes did not leave hers, and his face did not change, and the long, careful, gentle architecture of the man held steady and smooth. But she had watched the surface of that face for six weeks, she had learned its tides, and she saw something move far down in the dark water, a thing turning, a thing that did not want to be seen.

"Nothing that bears on your safety," Matteo said.

It was a true sentence, or it sounded like one. She turned it over in her mind, as she turned all of his sentences, and found no flaw in it. She saw the same slight, careful shape she had seen in the kitchen, in the corridor, on the pier. A door held not quite shut.

"All right," she said.

She did not say what she knew, which was that she had not told him everything either. She had not told him that she had written a number in her notebook with his initials beside it, and that it was still there. She had not told him that when he had said I poured it, she had believed him completely, and that she still did not know whether that was wisdom or the most dangerous folly of her life. It was her one reservation, and she meant to keep it, as he plainly meant to keep his.

She went to the door. At the threshold she stopped, with her hand on the brass, and looked back.

He was standing where she had left him, in the green pool of lamplight, with the old books rising dark behind him. He looked younger than she had ever seen him, and also very much older. In his face there was an expression she could not name: gratitude, grief, and beneath them both a faint, stubborn, terrible hope.

"Goodnight, Matteo."

"Goodnight, Sienna."

She went out, and closed the door, and stood in the dark corridor with her back against the wood. The house breathed around her. Somewhere a clock ticked, steady and slow. In the library, behind the door, she heard a long, shaky exhalation, and then the soft creak of a chair, and then nothing.

She climbed the stairs alone, with one hand on the banister, and did not look back. In the east suite she drew the bolt and sat at the desk by the window, under the green lamp, and opened the notebook to a clean page. She wrote the date. She wrote, in a hand that was almost steady: Both remember.

She looked at the two words for a long time.

Then she wrote underneath: He is still keeping one thing from me.

And, a little lower, in smaller letters, with the pen pressed so lightly that it hardly marked the paper: So am I.