The east greenhouse stood at the end of a long path of trodden snow, and every pane of its curved glass roof had fogged white from within, so that from a distance it looked like a lantern someone had carried into the garden and forgotten to put out.

Alan arrived at five minutes to four. He had checked his watch on the path, and again at the corner of the potting sheds, and a third time with his hand already on the door. He wore a pressed shirt. He carried his notebook under one arm and a pen in his breast pocket, and he had rehearsed on the walk from the dormitory exactly what he would say if anyone asked why he had come. In a professional capacity. As co-author. It was a perfectly reasonable sentence. It had survived three days of examination and had so far shown no cracks.

From behind the door came the sound of a great many people being happy in a small space: laughter, a clatter of copper, somebody singing badly and with total conviction, and underneath it all a low gurgling thump, like a large animal clearing its throat.

He opened the door, and the heat hit him like a hand.

It was a wet, green, golden heat, thick with the smell of mint and warm earth and honey and, faintly, scorched copper. Long wooden benches ran the length of the glasshouse, crowded with cauldrons of every size and no two alike: squat black ones, tall thin ones, one that appeared to have been made from a repurposed bell. Baskets of trailing herbs hung from the iron ribs of the roof, dripping gently. Shelves along the far wall were packed with jars, each labeled in a different hand, some in careful copperplate and some in what looked like the result of a quarrel between a pen and a hen. A kettle whistled on a squat iron stove. Somebody had hung a string of dried chilies over the door, and somebody else, apparently in protest, had hung a string of lavender beside them.

It was not tidy. It was the opposite of tidy. Alan stood on the threshold with his notebook against his chest and felt, absurdly, as though he had stepped into the inside of a very large and cheerful pocket.

"He came!"

The cry rang out from the far bench, and every head in the room turned.

There were perhaps fifteen people there. Most were visitors, he gathered, first-years and second-years in twos and threes, holding cups and looking around with the guarded delight of people who suspected they were about to be asked to do something. But the cluster by the far bench was clearly the club proper, and at the center of it, with her sleeves shoved to the elbow and a stained leather apron tied twice around her waist, stood Elen Joy. Her hair was knotted up in a length of kitchen string. There was a smear of green across her jaw. She was beaming at him as though he were a ship that had been given up for lost.

She crossed the greenhouse at a half run, weaving between benches, and caught his sleeve before he could retreat.

"You actually came. I said four and you came at five to, I knew you would, I told them you would." She towed him toward the bench with the gleeful ruthlessness of a tugboat. "Everyone, this is Alan Valemont. He's my co-author. He's here in a professional capacity."

A small silence fell. Then the cluster at the bench exploded in laughter.

"A professional capacity," said a tall, dark girl with a long braid, eyebrows like two drawn blades, and a nose that seemed to flare slightly, as though she were taking his measure by scent. "Oh, that is perfect. So this is the wall."

"I beg your pardon?" said Alan.

"She says it fondly," said the girl. "It's a term of endearment."

"I do!" Elen agreed warmly. "It's a very good wall. Wren, be nice."

"I am being nice. I haven't even asked him his favorite poison yet."

"I do not have one," said Alan.

"Everyone has one."

"Hemlock," said Alan, after a pause, "from a historical standpoint. It was widely misused."

Wren's eyebrows rose, slowly, in two perfect arcs. "Classical. Safe. Slightly dull." She considered him. "I like him."

"Wren is the one who can smell a bad batch from across a room," said Elen, in the tone of one introducing a minor deity. "She's never been wrong. It's frightening."

"Once," said Wren. "And it was a very ambiguous cheese."

There were four of them, Alan gathered, and they closed round him in turn. The big sandy boy with soot ground into one cheek and both eyebrows slightly singed was Theo, who shook his hand with enormous enthusiasm and said, "Welcome, welcome, don't stand near that one," jerking a thumb toward the squat black cauldron on the next bench, which was at that moment emitting a long, low, thoughtful burp of violet smoke.

"That's perfectly normal," Theo added, a shade too fast.

"It is not," said a calm voice.

The girl who stepped forward was small and square-shouldered, in a neat gray cardigan, with a ledger tucked under one arm and a pencil behind her ear. She looked at the cauldron the way a patient mother looks at a child who has been into the jam. Without any fuss, she took a bucket of sand from beneath the bench, tipped it over the violet smoke, and the smoke subsided with a faint, offended hiss.

"Mira," she said, extending a hand to Alan. "I keep the stores. And the books. And, apparently, Theo."

"I'm a man of ideas," said Theo.

"You are a man of three destroyed cauldrons since September."

"Two and a half."

The fourth stood a little apart, by the end of the bench, a thin, serious boy with ink-stained fingers and a very large old book held against his chest like a shield. He nodded to Alan when Elen said his name was Dara, and said nothing at all, and Alan, who knew something of the art, nodded back.

He had expected, he realized, to be uncomfortable. He had prepared for it. What he had not prepared for was how quickly the discomfort turned into something else. They did not stare. They did not interrogate him for long, and when Wren's teasing grew sharp, Mira said her name once, quietly, and it stopped. Somebody put a stool behind his knees and said, "Sit, it's the only one that hasn't been singed." Somebody else pressed a cup of hot tea into his hands. And Elen, who had been talking to three people at once, glanced back at him with a flash of that quick, private, entirely uncomplicated gladness, and tossed him an apron.

"Put that on. Theo's cauldron has opinions."

He put it on. He looped the strings behind him, found that the knot would not hold, and felt a hand come in beside his elbow, light and brisk and smelling faintly of mint, and tie it for him in a single quick tug.

"There," said Elen. "Now you're one of us."

"I am a visitor."

"With an apron," said Elen, "it's practically a membership."

The teacher arrived at ten past four, through a side door nobody else seemed to know existed.

He was a very tall, very thin man with white hair that stood up in a dandelion cloud, wearing a waistcoat buttoned one hole out and two different socks, one gray, one green. He carried a copper watering can in one hand and, in the other, a half-eaten apple, and he walked through the greenhouse humming under his breath with the air of a man who had been somewhere else for several hours and was not entirely sure where.

"Ah," he said. "Tom. Marta. Ellen, hello. Wendy. And, ah."

"Theo," said Theo. "Mira. Elen. Wren. Dara."

"Quite so," said the professor, entirely unembarrassed. "Quite so. Thank you." He looked at Alan. His eyes, in his lined and sleepy face, were very pale blue and, for a second, extraordinarily sharp. "And this is the visitor. Valemont."

"Professor Marlow," said Alan, rising.

"Sit, sit. Open evening, article twelve, subsection c." He recited it in a pleasant singsong, as though he were reading a recipe. "All visitors shall be offered water, informed of the location of the exits, and not permitted within the radius of an active cauldron without a protective garment. Exits, two. Water, there." He pointed with the apple. "Garment, yes, very good, I see Miss Joy has attended to that. A tidy name, Valemont. We have too little of it in here."

Alan stared. He had known the article. He had not known that it was so exact, or that it could be said so well by a man who had just called Wren Wendy.

"You are correct, sir," he said.

"I generally am about rules. It is people I get wrong." The professor smiled, a vague kind smile, and drifted away along the bench, watering a row of seedlings with great tenderness and an occasional word of encouragement. "Good evening, Marigold. Don't sulk. You are doing very well."

"He's talking to the plants," said Elen, at Alan's shoulder.

"I assumed."

"He's the best teacher in the school. He doesn't know anybody's name." She said it with so much love that something shifted in Alan's chest. "But he's never once made a rule up on the spot or let someone else's rule be bent for the wrong person. He says rules are for the weakest person in the room. Everybody else can look after themselves."

Alan filed that away, slowly, carefully, as one files something that is not yet clear.

It was a small thing that he noticed next, and he would not have noticed it at all if he had not been trained from childhood to read the edges of rooms. On the noticeboard beside the door, among curling slips of paper advertising lost cauldrons, newt futures, and a fight club for first-years (denied, in a different hand), hung one sheet of heavy cream parchment, with a clean red seal at its foot and a script so neat that it seemed to have been drawn with a ruler.

Notice of Annual Inspection. The Potions Club shall be examined for compliance with Academy standards on the second Friday of next month. Signed, with the compliments of the Council, Aldric Voss.

It was a perfectly civil notice. It said please and thank you twice.

He had not realized that the professor had come up beside him until the old man's hand, resting for a moment on the corner of the board, went very still.

It was only a moment. The pale eyes read the notice once, without moving, and the long jaw tightened under the loose skin like a drawn cord. The watering can did not wobble. The humming had stopped.

"Ah," said Professor Marlow, lightly. "The inspection. Annual. Delightful."

"He looks at my cauldron like it's personally insulted him," said Theo, cheerfully, from the bench.

"Mr. Voss looks at everything that way," said the professor. "Be polite to him."

"He always smiles, though," Wren said.

"Yes," said Professor Marlow.

It was one word, perfectly flat. Then he turned from the board, and the vagueness came back over his face like a curtain drawn, and he said brightly, "Who would like more tea? I believe there is a ginger one in the blue pot."

Alan said nothing. He added it to the list he did not know he was keeping.

At half past four, Elen clapped her hands.

"Open evening tradition!" she called. "One of us shows the visitors what we do. Tonight it's me, because I asked first, and also because Theo isn't allowed."

"Once," said Theo, wounded.

She took the middle bench. The visitors drifted in, cups in hand, and the club made space around her without a word, as one makes room for a sun. She set a small cauldron on the burner, pushed her sleeves higher, and for a moment, before she spoke, she was quiet. Alan saw her fingers brush the rim of the pot, lightly, almost reverently, the way she had touched the bark of the great tree in the forest. Then she looked up.

"Right," she said. "Who here has been scared of a potion?"

Hands went up. Quite a lot of them.

"Good. You should be. They're dangerous." She reached behind her and took down a jar of silvery-green leaves. "This is sleepwort. If I put one thimble of it in a cup of warm milk, a restless child goes straight to sleep and wakes up happy. If I put a ladleful of the same leaf in a pot of stew, a grown man sleeps for a week. Same plant. Same leaf. The only difference is the hand that picks it up."

She let that sit.

"That's all a poison is," she said. "A medicine nobody introduced properly."

"I am going to use that in the inspection," said Professor Marlow mildly, from the back.

Laughter ran round the benches. Elen grinned and set to work.

She worked fast and she worked without wasting a single motion, and she talked the whole time, explaining as she went. She called the frostmint by its old name and told them where it grew. She showed them how to crush it without bruising the oil, and where the heat should sit in the pot, and when to stop stirring and let the thing alone. Her hands were sure. The knuckles were smudged with ink, the nails short, and the heel of one palm stained green, and not once did they hesitate. Her whole face had changed. It had a clear, bright, absorbed look he had seen only once before, on a window seat at night, watching snow.

"Three turns," she said. "Left. Slow. Don't force it." Her spoon went round, once, twice, three times. "Now watch."

The surface of the cordial shivered. Then, one by one, on the dark liquid, tiny feathers of frost began to bloom. They spread out from the center in delicate silver ferns, each as fine as lace, and hung for a moment on the surface of the cup before melting into a fragrance of mint and snow that drifted across the greenhouse and made every visitor in the room sigh at once.

"It doesn't do anything," Elen said, laughing at their faces. "Not really. It's only pretty. But I think pretty is allowed, as long as you say so."

She ladled it out and passed the cups round. When she handed Alan his, her fingertips brushed his over the rim, and her eyes met his, bright and a little shy, as if she were asking something she did not quite dare to say.

He took a sip. It tasted of cold air and green mornings.

He had come to see what she loved. That was what he had told himself on the path. And he had expected, he now realized, to see it the way one sees a thing across a room, as a subject to be catalogued. Potions. Plants. A hobby of a lively girl.

But he was not looking at the cauldron. He had not been looking at it for some minutes. He was looking at the faces turned toward her, and there were a great many of them, and every one of them was lit. Mira, with her pencil forgotten in her hand and her whole stern little face gone soft. Theo, grinning like a child at a conjuring trick. Wren, with her chin propped on her fist, wearing the helpless expression of someone watching a friend do the one thing the friend was made for. Even the visitors, the stiff first-years who had arrived braced for lectures, were leaning in with their cups forgotten, and one of them had actually forgotten to be afraid.

He could not have said how he knew where the sun was. But he knew it the way one does in winter, without looking. By the faces turned toward it.

"Dara," said Elen. "Will you read the line from the old herbal? The one you found."

The thin boy went white.

"No," he said, to the cover of his book.

"Just to us. Nobody else is listening." She said it gently, with a nod toward the visitors, who had at once, with perfect tact, turned and begun talking among themselves. "You don't have to. But it's so good. I think you ought to hear how good it is out loud."

He stood a long moment with the heavy book in his arms. Then he opened it on the bench with fingers that shook very slightly and bent over the page, and began to read in a voice so low that Alan had to lean in to hear it. It was a language Alan did not know, old and rounded and strange, all soft consonants and falling vowels, like water being poured from one jar into another.

When it was done, Dara swallowed, and in a thread of a voice he said, "It's about the root. It says that what heals and what harms grow from one root. And that it is the hand which decides."

There was a silence. A good one. Theo let out a long breath and said, "Dara, that's the best thing anyone's said all year," and Dara went the color of a ripe beet, and Mira slid an arm round his shoulders without a word. Elen squeezed his elbow once, quick and warm, and said nothing at all, and Alan noticed that she did not say well done or look at him in triumph. She had simply given him a place to stand and then stepped back.

It was only then that he understood what she did, and he sat very still with the cup in his hands.

She did not make people brave by pushing them. She made them brave by standing next to them. And she did it so lightly, so easily, that the people she did it to never noticed they had crossed a line at all.

He thought of the courtyard, and the pale boy by the fountain whom the Warden had singled out, and the way a hundred snow-birds had come down out of a clear sky at precisely the right moment. He had not seen it then. He had seen only the noise.

"Mr. Valemont," said Mira.

He turned. She was standing at the stores cabinet at the end of the greenhouse with the ledger open on the shelf in front of her and a pencil gripped in her fist, and there was a small, hard, familiar crease between her brows. It was the look of someone who has added the same column four times.

"I'm sorry to ask," she said. "Elen says you are very good at ledgers."

"Elen is biased."

"Elen is right about most things that are not rules," said Mira dryly. "My nightroot extract is three vials short. I have counted four times. The shelf says forty-one. The book says forty-four. If the Council finds a discrepancy on the second Friday, they will tell Professor Marlow it is a security matter, and he will not defend himself, because he will assume it is his fault."

Alan looked at the ledger. He looked at her face. He had a clear and rather alarming sense that if he said no, he would be able to live with it, and that he did not want to.

"May I?" he said.

It took six minutes.

He read the ledger from the top, as he read everything, with a finger moving down the margin and his lips pressed together, and by the third page he had the shape of Mira's hand in his head, the way she wrote her sevens, the way she carried totals. By the fifth, the shape of the error had begun to show, like a pale stain coming through paper. He turned back two pages. He turned forward. He ran his finger down a column and stopped.

"Here," he said.

Mira leaned over.

"Three vials of nightroot, entered on the fourteenth under spoiled stock. And here, again, on the same day, under consumed in practical." He tapped the line. "The same three vials. It has been subtracted twice. This is the day of the cauldron."

There was a long silence.

"Theo," said Mira.

Theo, who had been drifting closer with an expression of eager innocence, froze.

"I was being thorough," he said.

"You recorded the explosion as spoilage and as consumption."

"It was both! It spoiled and then I consumed it. Some of it. Through my eyebrows."

The cheering that went up was so large that the visitors turned round. Mira put down her pencil and, for the first time in Alan's acquaintance with her, laughed outright, a quick astonished bark of a laugh that made her look about twelve years old. "Three days," she said. "Three days I've been up at night over this." She seized his hand, shook it hard, and said fiercely, "Where have you been all term?"

"Being a wall," said Wren, from the bench, with satisfaction.

"We'd like to invite you to audit the stores, Mr. Valemont," said Mira. "Formally. Whenever you have an hour. We'd be honored."

And there it was. He felt it arrive, the thing he had known would arrive since he walked through the door. A quiet, expectant, kindly silence. The faces turned toward him. Dara, with his book. Theo, hopeful as a hound. Wren, one eyebrow lifted, watching him without mercy. The club, offering him a seat.

He thought of his father's letter. He thought of a drawer in the dormitory with two sheets of paper in it, and a line he had read twice. A Valemont is judged by the company he is seen to keep.

He thought of the ledger, and of Mira's three nights.

He did not look at Elen. She was at the far bench, wiping her cauldron, with her back to him, and she was being so very elaborately casual about it that her ears had gone pink. She did not turn. She did not say a word. He understood that she was not going to, and that she would be as content as if he had said yes whether he said it or not, and it was this, more than anything, that made it hard to refuse.

"I will audit the stores," said Alan. "Once."

"Once," said Mira, with great satisfaction, "is how it starts."

"Log it, Marta," Professor Marlow called from the seedling shelf, without looking round.

"Mira, sir."

"Mira. Yes. Log it, Mira. A promise, however small, goes in the book. A rule, Mr. Valemont" and here he did turn, with the watering can in his hand and an apple core in his waistcoat pocket, "is a promise a group makes to its weakest member. Write it down. Sign it. And keep it."

Alan found, rather to his surprise, that he had nothing to say. He only nodded, and the old man nodded back, and went on watering.

By six the light outside had gone violet and the glass roof glowed like the inside of a shell. The visitors had drifted away in twos and threes, carrying empty cups and a faint smell of mint, and the club had fallen to the slow, contented business of clearing up. Alan removed his apron, folded it with exact corners, and laid it on the end of the bench.

"Walk him out properly, Elen," called Wren, from somewhere under a sink. "He's a guest."

"I was going to!"

"I know you were. I'm being supportive."

The door of the greenhouse let out into the garden, and the cold was a clean shock after the steam. The snow had begun again, in thin slow flakes that drifted down through the blue dusk, and the lamps along the path had come on one by one, so that the whole garden seemed to be lit from underneath. Elen came out behind him still in her apron, with the string loose in her hair and a smear of mint on her wrist, and shut the door against the heat.

She stood there with her arms wrapped around herself. She was not talking. For Elen, it was almost eerie.

"Well," she said at last. "That's the club."

"It is."

"Is it terrible?"

"It is," said Alan, with care, "extremely disorganized."

"I know."

"There is a toad in the sink."

"That's Gerald. He's a founding member."

"And the labeling system," said Alan, "is not a system."

"I know!" She was laughing, but under the laughter, he noticed, she was watching his face, quite carefully, the way she had watched the cordial before it bloomed. "So. What did you think?"

He opened his mouth to say something correct.

"What do you think I love?" Elen said, before he could. It came out in a rush. "I said I'd show you. I'm not sure I did it right. It's not really the potions. I mean it is, but it isn't. It's hard to say. I'd like to know what it looked like from outside."

The snow came down between them. Somewhere behind the glass, Theo began to sing again, and a loud and cheerful voice told him to stop.

Alan looked at her, in the lamplight, with the flakes catching in her hair, and she looked back, entirely unarmored. He thought of a ring of salt around a root. Of a boy with a book held against his chest. Of her fingertips brushing the rim of a cup.

"People," he said.

Her breath caught.

"You love people. The poison is only the means. What you like is," he searched for it, with the same care he would have given a proof, "making them braver. You find the thing they are afraid of and you stand next to it until it is small. I do not think you know you are doing it."

Elen stood very still.

She did not say anything for what felt like a long time. The dimple did not come. Her face did something quiet and uncertain, like a person who has opened a door in her own house and found a room she did not know was there, and her eyes were very bright.

"Nobody's ever put it like that," she said, in a small voice.

"I was speaking," said Alan, a little stiffly, because his ears had begun to burn, "professionally."

"Of course."

"As your co-author."

"Of course you were." She looked down at her hands, and then up, and the smile that came was not the broad one at all. It was small, and shaky, and went all the way to her eyes. "Your turn, someday. For what you love. I'm not going to forget."

"I am aware."

"Good." She stepped back toward the door. "Thank you for coming, Alan. Truly. Goodnight."

"Goodnight, Elen."

He made it halfway down the garden path, with the snow tickling his neck and his heart doing something unreasonable in his chest, before he realized that he had left his pen.

It was in the breast pocket of his shirt when he had arrived. He remembered taking it out to check the ledger. He stood in the lamp-glow, weighing the matter, and concluded that a person of good order did not abandon a pen on foreign territory, and turned back.

The greenhouse door was ajar. The inside lamps had been turned down, and most of the club had gone. Through the long gap he could see the benches, empty and gleaming, the stove ticking as it cooled, the dark ranks of jars.

And in front of the noticeboard, quite alone, stood Professor Marlow.

He was not humming. The watering can lay forgotten at his feet. He stood with both hands behind his back, quite straight, and he looked, in the dim light, a good deal taller than he had seemed, and a good deal older. His whole face had changed. The vagueness was gone. What was left was tired and clear and very quiet, and it was turned toward the cream-colored notice with its clean red seal, as one turns toward the window of a house in which one used to live.

Alan stood in the doorway without speaking. He could have gone away. He was not sure why he did not.

"Mr. Valemont," said the professor, without turning. "You forgot something."

"My pen, sir."

"On the third bench. By the sleepwort."

Alan fetched it. When he came back, the old man had turned, and was looking at him in the lamp-glow with those pale, clear, unclouded eyes.

"May I ask you something?" said Professor Marlow.

"Of course, sir."

"Do you believe that rules protect people?"

It was not a casual question. Alan could hear that. He stood with the pen in his hand and found, to his own surprise, that he did not need to think.

"Yes," he said.

"So do I." The old man nodded slowly. There was no triumph in it. "So do I. That is why I am so afraid of the men who make them for themselves."

He held Alan's eyes a moment longer. Then something went over his face, quick and small, like a hand drawing a curtain, and the old vague gentle smile came back, and he stooped and picked up the watering can.

"Do not mind an old man," he said. "It is only the steam. It gets into the brain. Good night, Mr. Valemont. Mind the step."

Alan went out into the snow.

Behind him, the lamps in the greenhouse went down one by one, until only the red seal on the cream-colored page gleamed faintly in the dark, a small bright drop of wax, like a closed eye.