The letter arrived on a Thursday.

She knew it was Thursday because she had been counting days, which she had started doing on the second day in Bellgrave when she realized that time in Avelune passed at the same rate as time anywhere else, which was both reassuring and slightly inconvenient given that she had no way of knowing how it corresponded to time on the other side of the door she had fallen through. She marked Thursday in the leather-bound book with a small T in the corner of the page, the way Agnes had marked Saturdays in her appointment ledger, a habit absorbed in childhood.

She was on the third shelf of the section labeled Threshold when she heard the envelope slide under the door.

Not the front door of the shop, which Cassian kept locked until he opened officially. The door to the back room, which was the door she had started thinking of as her door, the door she used when she wanted to come in or go out without going through the shop. She had been given a key to this door three days ago, handed over without ceremony or explanation, and she had added it to her coat pocket next to the letter from Agnes and had not mentioned either of these things to anyone.

The envelope was plain. White, unsealed, lying on the flagstone floor where it had been pushed through the gap beneath the door. On the front, in handwriting she did not recognize: Mina.

Just her first name. No surname. No indication of who had written it or how they had known to push it under this specific door.

She picked it up and stood with it for a moment, turning it over. Nothing on the back.

She opened it.

Inside was a single folded sheet of paper and a single line of text, in the same handwriting as the envelope: Do not let Cassian remember.

She read it three times.

She was, she found, not frightened, which surprised her slightly. She was unsettled, which was accurate, and alert, which was correct, but not frightened. She had a working theory, which was that Cassian was connected to something dangerous and that the world that contained him also contained people who had strong feelings about that danger, and this letter was a product of that situation rather than a direct threat to her. She held this theory loosely, because it might be wrong, but it gave her enough stability to think.

She thought about what the line meant.

Remember was specific. Not find, not learn, not be told: remember. Which implied that what he was looking for was something he had once known, something that was inside him already in some form, something that had been removed. The way his Afterglow had been removed. A removing rather than an absence.

Someone did not want him to recover what had been removed.

And that someone knew her name and knew which door she used.

She folded the letter and put it in her pocket with Agnes's and went to find Cassian.

He was at the front of the shop, moving books from one crate to another and noting them in the ledger, a task that required both hands and his attention, and he looked up when she came around the shelf and saw whatever was on her face, because he set the book down immediately.

She handed him the letter.

She watched him read it. She had become skilled at reading Cassian reading things: the pace of his eyes, the point at which they slowed, the particular quality of the stillness that settled over him when something registered as significant. He went still almost immediately, which meant the line had hit before he had finished the second word.

He read it twice. He folded it again.

"Where did you find this?" he said.

"Under the back door," she said. "Ten minutes ago."

He looked at the letter in his hands. Then at her. "Are you all right?"

She had expected: who sent it, do you know who left it, what did you do when you found it. The question he asked instead was a different category, and she noted it.

"Yes," she said. "A little unsettled. Primarily curious." She paused. "It frightened you."

"It is concerning," he said, which was the controlled version of what she had said. She gave him the translation: yes.

"Someone knows I am here," she said. "Someone knew which door to push it under. Someone knows my first name."

"Yes," he said.

"And they do not want you to remember something."

He was quiet.

"You know what they mean," she said. "By remember."

He looked at the letter again. "I have a theory," he said.

"Tell me."

He set the letter on the counter. "When I erased my Afterglow," he said, "I removed the record. What I could not remove was the event itself, the thing I had seen. It exists in my memory, or it did." He paused. "Over the years, the memory has become less clear. I believe this is a natural consequence of the erasure: the thing you remove from the record begins to lose coherence in the other places it exists, because the record was the source. The anchor." Another pause. "I remember less of what I saw than I did when I first saw it. I remember less every year."

She thought about this. "So to recover what you had," she said, "you would need to recover the memory."

"Or reconstruct it from the fragments," he said. "Which amounts to the same thing."

"And someone does not want you to do that."

"So it appears."

She looked at the letter on the counter between them. At his hands on either side of it.

"The letter came to me," she said. "Not to you."

"Yes."

"Which means whoever sent it believes I have the ability to help you remember." She looked up. "Or they believe I have reason to want to prevent it."

He was very still. "Do you?" he said.

"Have reason to want to prevent it?"

"Yes."

"No," she said. "We made an agreement. You help me find my way back; I help you find what you are looking for. I am not going to take instructions from anonymous letters to undermine the person I made that agreement with."

He looked at her for a long moment.

"You could have not told me," he said. "You could have read the letter and said nothing."

"Yes," she said. "I could have."

"Why didn't you?"

She thought about this with the specific honesty she applied to questions that deserved it. "Because keeping it would have been a kind of deciding," she said. "And I told you I did not want you making decisions for me. It follows that I should not make them for you either." She paused. "We agreed to work together. This is information that affects the work. You should have it."

He looked at her with an expression she had no name for yet. She was working on it.

"The letter is also information about who is watching us," she said. "Someone has been watching the shop. Someone knows my name and my habits and which door I use, which means they have been watching me since I arrived or they have sources of information I do not know about yet." She picked up the letter and looked at it again. "The handwriting is educated. Careful. The paper is high quality. Whoever this is, they are not acting out of desperation, they are acting out of calculation."

"Yes," he said. "That is consistent with my theory about who it might be."

"Who?"

A pause.

"Someone who knew my Afterglow before I erased it," he said. "Someone who has reason to want the event within it to remain forgotten." He picked up the letter and folded it again with precise movements. "There are not many people who fit that description."

She watched him fold the letter. His hands were very controlled.

"You are frightened," she said, not as an accusation.

He looked at her.

"I am concerned," he said.

"I know what concerned means, from you," she said. "I am becoming familiar with your vocabulary. I am asking because it is relevant: if you are afraid of this person, I need to know that."

He held the folded letter for a moment.

"I am not afraid of this person," he said. "I am afraid of what it means that they have found you already." He set the letter down. "You have been here less than a week."

She absorbed this. He was afraid for her. Not of the situation in the abstract, not of being exposed or found: afraid for her specifically.

She felt this land somewhere and decided not to examine where.

"Then we work faster," she said. "What do we do next?"

He picked up the ledger and set the crated books aside, the task abandoned for something more urgent. He had made the decision she could see him making: less caution, more information. Something about the letter had tipped the balance.

"There is a person I should speak to," he said. "Someone who was in the archive when I found the Afterglow. He has information I did not ask for at the time." He looked at her. "Will you come? Your ability may help."

"Yes," she said. "Of course."

He put on his coat, and she put on hers, and in her coat pocket were two letters from two different people who knew more than they had said, and outside the city of Bellgrave was going about its afternoon, and she thought: someone is watching this shop, and they know my name, and they sent the letter to me.

Which meant they thought she was the variable. The new element. The thing they had not accounted for in their calculation.

She thought: good. Let them think that.

She thought: they are not wrong.

She followed Cassian out into the afternoon, into the streets of the city she was learning, and behind her the shop door closed, and on the table inside was the list they had made together, and at the top of it was a name that would matter later, and none of the people in this story were yet ready for what it meant.

But they were moving. And movement, in her experience, was where stories began to resolve.

She touched the letters in her coat pocket and kept walking.

The person Cassian wanted to speak to was named Aldred, and he lived above a clockmaker's shop two streets from the river, and he was, from the appearance of his sitting room, either very old or very interested in the appearance of being very old.

Mina sat in the chair nearest the window and looked at the room while Cassian and Aldred went through the preliminary conversation. The chair was red velvet, worn to nap in the places where someone had sat in it for many years. The walls were covered in framed documents and drawings, the kind of room where someone had spent a lifetime collecting and had long since given up organizing. Near the window, a shelf of books, the spines worn and the titles indistinct from where she sat.

She reached toward the nearest book on the shelf, the closest one, and stopped herself.

She looked at Cassian.

He gave her the faintest nod.

She touched the nearest book's spine.

The Afterglow from it was old and very clear, as though the age had concentrated rather than diluted it: a room, a table, documents spread across it, and several people seated around it including a young man she recognized even in this older version of the archive, a younger Cassian, perhaps seventeen or eighteen, bent over something he was reading with the focused attention she knew from the current version of him. The image was still, not an action but a state, the way certain Afterglows captured a condition rather than an event.

And in the corner of the image, barely there, a woman with silver hair leaning over someone else's shoulder to read the same document.

She let go of the book.

Aldred was speaking. She pulled her attention back.

"The boy was brilliant," Aldred was saying, to Cassian, about someone she gathered was Cassian: the old man's way of speaking about the past used the present as reference rather than the past. "Went through the advanced catalog methodology in half the time it took anyone else. His family was pleased. His father came in personally to say so, which was not a thing Vey Senior did often."

"You remember," Cassian said, with the neutral quality of a question that was not quite a question.

"I remember everything," Aldred said, with the satisfaction of someone who considered this both a skill and a virtue. "The question is what you are asking me to remember specifically."

"The day I found it," Cassian said. "The fragment in my record."

Aldred was quiet for a moment.

"You were not supposed to be in that section," he said. "You knew that."

"Yes," Cassian said.

"But you went anyway, because the section was relevant to work you were doing on the family archive, and you thought you could access the peripheral material without touching the primary records."

"Yes."

"And you touched the primary records."

"Yes."

Aldred sighed, which was the sigh of someone who had spent many years sighing at the particular variety of intelligent young person who believes that rules are provisional guidelines for people less capable than themselves.

"The girl was there," Aldred said. "The Voss girl. Elara."

"Was she with me when I found it?"

A pause. "She was in the archive," Aldred said. "Whether she saw what you saw, I cannot say for certain. But she was there when you came out of the primary records section." Another pause. "I remember her expression. She knew something had happened."

Mina watched Cassian.

He was very still.

"What happened after?" he said.

"You came to me," Aldred said. "You told me you had found something in your record. You did not tell me what, but you asked me whether the future shown in an Afterglow could be altered. I told you yes, with sufficient skill and the right intervention, it was possible. The same as I had told you in your theoretical training." He paused. "You left. You came back three weeks later and you told me you had done something that I should not ask about."

"You did not ask."

"I did not ask," Aldred confirmed. "Because I had my theory and I preferred not to have it confirmed." He was quiet. "I have had, in the years since, a number of chances to revise my position on that choice. I have not fully resolved whether I should have pressed you."

Mina looked at the framed documents on the wall. At the old man who had chosen not to ask and lived with that choice for five years.

She thought about all the people in this situation who had been choosing not to ask, or not to tell, or to wait, or to hope that silence was the same as prevention. She thought about the specific shape that produced: silence all around a thing that was still happening anyway, in the dark, without witnesses.

She thought: that is the cost. Not just his cost. All of their costs.

"Thank you," Cassian said to Aldred.

They left.

On the street she walked beside him and let the silence be what it was for two blocks.

Then she said: "He knows more than he told you."

"Yes," Cassian said.

"He knows whether Elara saw what you saw."

"Yes."

"But you did not press him."

"No," he said.

She looked at him. "Because you already know she saw it."

He was quiet for half a block. Then: "I believe she did. I have believed it for some time. I wanted confirmation from an outside source before I acted on the belief."

"And now you have it."

"Now I have it," he said.

She thought about this, about the difference between believing and knowing, about the way confirmation changed what you were allowed to do with the information. She thought about Elara Voss with the silver hair in the archive five years ago, watching, knowing, making her own choices in response to what she had seen.

"She watched you remove the Afterglow," Mina said. "She saw it happen."

"Yes," he said.

"And then she spent five years watching to see what came next." She paused. "And what came next was me."

He looked at her briefly, sidelong.

"Yes," he said.

She walked beside him through the evening streets of the city that was becoming familiar, and she thought about being the next thing in a sequence that had been running without her for five years, the variable that had arrived, the element that changed the calculation.

She thought: I am the next move in a game that was already in progress.

She thought: that is all right.

She thought: I have always been better at the middle of things than the beginning.

She touched the letters in her pocket and kept walking.

At the shop, he held the door and she went in, and the familiar warmth of it was there, the books and the lamps and the particular smell of cedar and old paper, and she stood in the middle of it and felt, for the first time since she had arrived, that she was somewhere rather than somewhere else. The distinction was subtle and total.

She took off her coat.

"I need to think," she said. "About Elara and what she wants and what it means."

"Yes," he said.

"Tomorrow," she said.

"Tomorrow," he agreed.

She went upstairs.

She lay on the bed and held the leather-bound book and thought about Agnes's patience and Aldred's silence and Elara's watching, all of the people who had been waiting for the next thing to happen. She thought about being the next thing.

She wrote, in the book, in pencil: Someone has been waiting for me without knowing they were waiting. Several someones. I arrived and the sequence continued.

She wrote: I wonder whether the sequence knows where it is going.

She wrote: I think I am beginning to.

She closed the book and fell asleep with her hand on the cover, and outside the city of Bellgrave went about its quiet hours, and in the archive two streets from the river an old man sat in his worn red chair and thought about choices, and across the city a woman with silver hair was thinking about the same thing from the other side of it.

The story was moving. Everything was moving.

Soon it would be time to see where.