From the Agreement of Temporary Cooperation, Clause 6: "Kissing is permitted only where strictly required for the performance, with not less than one hour's notice, and then on the cheek or forehead only."

Sun Mei came back to Yunxi on a Thursday, on the same bicycle, with the same enormous canvas bag and a list.

"Five poses," she said, spreading it on the counter of the tea house like a general unrolling a map. "The campaign leaflet needs a spread that says natural. I have been doing this for nine years and I can tell you that natural is the most difficult thing in photography, because nobody on earth is natural when a lens is pointed at them. So we cheat. We rehearse until it looks like we didn't."

"What are the poses?" said Wenxi.

She was wearing the old waxed coat. She had been wearing it for four days, on the grounds that the weather might change, and so far the weather had refused to cooperate. It came down to her knees and the sleeves had to be rolled three times. Tang Rui, behind the counter, had looked at it on Monday and said nothing at all, which was in itself a speech.

"One, leaning shoulder to shoulder," said Sun Mei, tapping the list. "Two, looking at each other. Three, laughing. Four, his arm round her waist. Five." She paused, and looked over the top of her round glasses with great relish. "Foreheads together."

There was a silence in the tea house. A teaspoon rang somewhere.

"Which of these," said Chengyan slowly, "is the one you most want?"

"All of them. But the last one is the cover."

He rubbed the back of his neck.

The studio was the upper room of the old rice warehouse by the east dock, a long bare space with whitewashed beams and tall windows that let in a clean grey light. Sun Mei had rigged a backdrop of plain linen against one wall, and a high stool, and two reflectors made of silver card and bamboo. There was a full-length mirror propped against a pillar. It was, Wenxi thought, a room designed for finding out exactly how you looked when you were lying.

"Shoulder to shoulder," said Sun Mei. "Go."

They stood against the linen. They leaned. It was like watching two planks being propped against a wall.

Click.

"No," said Sun Mei. "Lean as if you want to, not as if you've been told to. Wenxi, you are standing on the outside of your feet. Chengyan, you are holding your breath. Breathe out. There. Let your shoulders go."

He let them go by about a millimetre. She felt it through the wool of the coat.

Click.

"Better. Now, look at each other."

They looked at each other. It lasted two seconds. Wenxi saw his eyes, dark and level and serious, and a small muscle jump at the corner of his jaw, and then she felt her own face begin to do something she could not control, a kind of helpless tightening, and she looked at the ceiling.

"You are both looking at the ceiling," said Sun Mei.

"It's a very nice ceiling," said Chengyan.

"It has a beam," said Wenxi.

"It has a crack," said Sun Mei, "and it is not what I am paying you to look at. Mirror."

She made them practise in front of the mirror, side by side, for twenty minutes. It was the longest twenty minutes of Wenxi's life. She had stood in front of mirrors all her adult life, in changing rooms and on stairs and in the toilets of hotel ballrooms, and had always known precisely what she would see: a bright, capable, composed young woman with a dimple. She had never had to stand beside anyone while she looked.

The woman in the glass was twisting the end of her ponytail round one finger. The man beside her had his arms crossed so tightly that his knuckles had gone pale. They looked like two people at a bus stop who had each just remembered the same embarrassing thing.

"Look at yourselves," said Sun Mei, from behind them. "No, not at each other. At the glass. What do you see?"

"Two idiots," said Wenxi.

"One idiot and one carpenter," said Chengyan.

"Which of us is which?"

"I don't want to say."

She laughed. In the mirror she saw the laugh arrive on her face, wide and unguarded, and she saw his mouth curve in answer, and for a second the two of them stood there, grinning like children, with the silver light on their faces, and the click of the shutter went off like a small bird.

"Oh, that's lovely," said Sun Mei. "Keep that. Whatever that is. Do that again."

"We can't," said Wenxi. "We don't know what we did."

"That," said Sun Mei, "is exactly what I mean."

Pose three was easy, because Wenxi had a plan.

She had thought of it the night before, lying under the peony quilt with the rabbit on the ceiling, and it had seemed to her a very sound plan indeed. Chengyan was most natural when he was trying not to laugh. He had a face like a locked door, and the harder he tried to keep it shut the more the light came through the cracks. All she had to do, therefore, was provoke him.

"Laugh," said Sun Mei. "Go on. Make each other laugh."

"Right," said Wenxi, and turned to face him with enormous gravity, and pulled the worst face she could manage.

It was a very bad face. She crossed her eyes. She pushed up the end of her nose with one finger and puffed out her cheeks, and then, for good measure, she let her tongue loll out of one corner of her mouth, like a duck with a head cold.

Chengyan looked at her.

He did not move. His face went perfectly smooth, the way it did when a customer asked him for a discount. A muscle twitched at his jaw. Another at the corner of his eye. She watched the effort come over him in waves, the rigid straightening of the shoulders, the careful blank stare fixed on a point just beyond her left ear, the long slow breath through the nose. He was magnificent. He was a statue of a man resisting a joke.

She wiggled her ears. She had always been able to do it.

He made a sound like a kettle.

It escaped through his nose, a sharp involuntary snort, and he clapped his hand over his mouth, and his whole body folded forward, helplessly, with his shoulders heaving. A great bark of laughter broke out of him through his fingers. He tried to stop it. He could not. He bent double with one hand on his knee and the other still pressed to his face, and the sound of it echoed round the bare white room, rough and delighted and entirely uncontrolled.

"Stop," he gasped. "Wenxi. Stop. You look like a, like a, "

"A what?"

"A very surprised fish."

"I'm a lovely fish," said Wenxi, with dignity, and crossed her eyes again, and he went down altogether and had to sit on the floor.

Click. Click. Click. Click.

Sun Mei had come out from behind the camera and was standing with the lens hanging from her hand, looking down at them with a face of shining joy. "Do you know," she said, "I have photographed four hundred couples. I have never once had a man laugh until he sat down."

They did the fourth pose after lunch.

It was the one Wenxi had been dreading most, and it turned out to be the worst, because it required nothing but standing still. Sun Mei posed them in front of the linen, side by side, and told Chengyan to put his arm round her waist, and then stood back with the camera and waited.

He put his hand on the air.

It was the only way she could describe it. His arm came round her, and his hand hovered at the side of her waist, a careful hand's width from the cloth of the coat, like a man holding a plate over a hot stove. He was not touching her. He was standing as close to not touching her as it was possible to stand. She could feel the heat of his palm through the wool, a faint ghost of warmth, and she could feel the effort it was costing him, a fine, sustained tremor in the forearm that she could have drawn from memory.

"You are not touching her," said Sun Mei.

"I am touching her."

"You are touching her coat's idea of her."

"It's a very thick coat."

"It is a coat," said Sun Mei, "that is going to be on the cutting-room floor in about ten seconds. Chengyan. Please. Put your hand on the girl."

He did not move. His eyes were fixed on the middle distance with a kind of stricken courtesy, and she understood quite suddenly that he was not being obstinate. He was waiting for permission. It had not occurred to him that the contract, with its limits and its clean white lines, had been written by two people who could not trust themselves, and that he was now being asked, by a stranger with a camera, to find out whether he could.

"It's not a clause," said Wenxi, very low.

"What?"

"Waists. It's not in the Agreement. Nobody wrote it down." She took a breath. She put her own hand over his, where it hung, and drew it in, slowly, firmly, until his palm lay flat against the curve of her side. "There. It's an interpretation."

His fingers closed on the wool. She felt the whole of him go quiet, from the shoulder down. She felt the warmth go through the coat as if the coat were not there at all, and the weight of his hand, steady and enormous and utterly careful, and she thought, I am going to have to be very sensible for the rest of the afternoon.

Click.

"Lovely," said Sun Mei, in a hushed tone. "Don't breathe."

She did not breathe.

It was in the next pose that the trouble began.

"Foreheads," said Sun Mei, and stood back with a small bright look of anticipation. "Pose five. Face each other. Close your eyes if you like. Lean in. Foreheads together, slowly, and hold. I'll do the rest."

Wenxi's mouth went dry. Her gaze flew to Chengyan's, and she saw his eyes, wide and dark and quite blank with alarm.

She knew what she was going to say a full second before she said it. It came out in a rush, and in a tone of such lofty, scrupulous precision that she hardly recognised her own voice.

"Clause six," said Wenxi.

Sun Mei lowered the camera. "I beg your pardon?"

"We can't. I mean, we can, but we aren't able to do it immediately." She was talking too fast. "There is a term in our arrangement. It says that any, any contact of this kind requires not less than one hour's notice. So that nobody is ambushed."

"An hour."

"One full hour."

"You have a notice period," said Sun Mei, "for foreheads."

"It's very clear in the text," said Chengyan, in a voice like a closing door. "I'm afraid we're bound by it."

Sun Mei looked from one to the other. She took off her round glasses, polished them on her sleeve, and put them back on. It took a long time. When she looked up again her face had arranged itself into an expression of tremendous, sorrowful patience, and the corner of her mouth was trembling.

"One hour," she said. "Very well. I will go and have a cup of tea. I will come back at half past three. And at half past three, if there is any further mention of clauses, I will take the photograph myself, with my own hands, and I will move your heads."

She went down the stairs. They listened to her go. The warehouse creaked and settled, and a pigeon walked along a beam.

"That was very professional," said Wenxi.

"Yes."

"We have an hour."

"Yes."

"What do we do for an hour?"

There was a pause.

"We practise," said Chengyan.

"Practise what?"

"Whatever it is."

They did not practise.

They spent the hour, instead, in the most violent quarrel they had had since the age of fourteen, conducted in whispers, on opposite sides of the room, over the question of who was going to begin.

"It should be you," said Wenxi, from behind the stool.

"Why me?"

"You're taller. It's easier to lean down than to lean up. It's physics."

"It's not physics. It's your idea."

"It was Sun Mei's idea."

"You invoked the clause."

"Because you looked as if you were going to faint!"

"I did not look as if I was going to faint. I looked as if I was thinking."

"You looked," said Wenxi, "like a man being measured for a coffin."

He opened his mouth. He closed it. He rubbed the back of his neck, hard. "I am simply saying," he said, with great dignity, "that if one of us has to do it, it should be the one who is better at it."

"And which of us is that?"

"Not me."

"I have never done it in my life!"

"Neither have I!"

"You have been told," said Wenxi, very distinctly, "by nineteen aunties, that you are a catch. You must have had some practice."

"I have had a cat," said Chengyan. "I have had a cellist. I have had a dentist, who asked me to open my mouth. It was not practice."

She put her face in her hands, and laughed until she had to sit down on the stool. The sound of it rang round the empty warehouse, and after a moment she heard his laugh come in under hers, low and cracked and exhausted, and when she looked up he was leaning against the pillar with his arms crossed and his eyes shut, shaking his head.

"We are the worst people in the county," said Wenxi.

"We are in the top five."

"Second place. Eighty-nine."

"Presentation, seven out of ten."

"It was the flour."

"It was an act of God," said Chengyan, and opened his eyes, and looked at her across twenty feet of golden dust.

The light had shifted. It came in low now through the tall windows and lay in long pale bars across the floor, and every mote of dust hung in it like a tiny star. His face was in half shadow. She could not read it. She only knew that he had stopped smiling, and that he was looking at her with that grave, steady, attentive look, and that the whole warehouse had gone quiet.

"Wenxi," he said.

"Yes?"

"I'll do it."

Her heart went somewhere very far down.

"All right," she said, in a voice that did not belong to her.

Sun Mei came back at half past three, with a paper cup and an expression of stern, businesslike neutrality. She found them standing in the middle of the room, in the bar of gold from the window, facing each other. They had not moved for some time. He had taken off his boots, for some reason, and was standing in his socks. Wenxi had taken off the coat and laid it over the stool.

"Is the notice period concluded?" said Sun Mei.

"One hour and four minutes," said Chengyan.

"Splendid. In your own time."

She lifted the camera. She did not say anything else.

Wenxi closed her eyes. It seemed the only thing to do. She stood with her hands at her sides and her eyelids shut, and felt the room go dark and warm, and listened to the small sounds around her: the pigeon on the beam, the distant slap of water at the dock, the soft careful creak of a floorboard as a man took one step forward.

She smelled cedar. She smelled oil and soap and the clean, faint sweetness of wood shavings, and underneath it something that was only him. A hand came up, very lightly, and touched her face. It was just a fingertip, at the edge of her jaw, a brief careful pressure like a man testing the grain of a board, and then it went away, and she felt him lean down.

His forehead came to rest against hers.

It was warm. That was the first thing she noticed. His skin was warm and dry and a little rough from the sun, and the weight of it was so slight and so exact that she felt it all the way down to her feet. His breath moved across her mouth. She could feel the tip of his nose against hers. She could feel his eyelashes, when he blinked, brush the side of her cheek, very soft and quick, like a moth.

She stopped thinking.

It was the most curious sensation. There was nothing in her head at all. No clause, no script, no email in a grey font. There was only the contact, the single warm point where two people touched, and the huge, humming silence round it, and the knowledge that if she lifted her chin by the smallest fraction of an inch, there were two centimetres between her mouth and his, and no rule anywhere in the world to stop her.

He did not move either.

She heard him breathe in. It shook. It was a long, ragged, carefully managed breath, and she understood that he was standing as she was, at the very brink of a thing, with his hands clenched at his sides so hard that she could feel the strain in the air around them.

One. Two. Three. Four. Five.

Somewhere behind them, so soft that it might have been the breath of the room, the shutter clicked.

"That's enough," said Sun Mei, very quietly.

Neither of them moved.

"That's enough," she said again. "I have it. I have it, and it is the best I have ever taken. You can stop now."

He lifted his head. Wenxi opened her eyes.

His face was a hand's breadth away and he was looking at her with an expression she had never seen on a human being, as though he had walked through a door in the dark and found himself in a room full of light. His lips were slightly parted. A line of colour lay across his cheekbones. They stood there for one second, two, with the air between them thin and bright as glass, and then he stepped back, carefully, as if the floor might break.

"Thank you," said Sun Mei, in a tone of enormous delicacy, and began to put away her lenses.

They walked home in silence.

It was the longest silence of the campaign. They went down the warehouse steps and along the dock and up the bluestone path in the evening, with the sky going orange behind the roofs and the swallows stitching it up, and not a word passed between them. She carried the coat over her arm. He carried his boots. Their shoulders did not touch. There was a great clean foot of air between them, and she felt every inch of it, like a rope drawn tight.

At the third flowerpot, he stopped.

"Wenxi."

She turned. She had her hand on the latch of her own back gate.

"The notice," said Chengyan. "The hour. I should say, I didn't, " He stopped. He rubbed the back of his neck, and she saw his whole face struggle, and then give up. "Goodnight."

"Goodnight," said Wenxi.

She went in. She leaned against the inside of the gate with her eyes closed, and heard his boots cross the cobbles, and heard the door of the workshop shut. She stood there for a long time.

Then she took out of her cardigan pocket the strip of red paper, soft with handling, and unfolded it, and held it in the last of the light. Age seventeen. CY: Still on her toes. SW: FLAT. Witness: the willow.

She thought of the warmth of a forehead against hers. She thought of a man who could not put his hand on a coat, and then could.

I am not standing on my toes, she thought, quite clearly, and did not know to whom she was speaking. I am standing flat. I have always been standing flat. And it is still not enough to reach.