From Grandma Su's recipe book, page five: "Rain is only water. It is what you have left uncovered that makes it a storm."

It began to rain at ten past midnight, three days after the banquet, and Gu Chengyan lay on his back in the dark and listened to it arrive.

First came a scatter of single drops on the tiles, hesitant, like someone knocking on the wrong door. Then a patter. Then the long, rising hush of real rain, soft and steady, and under it the deeper note of water finding its way down the gutters and into the canal. He knew this sound. In Yunxi, in the plum season, you were born knowing it. It was the sound of the whole town being gently washed.

He did not sleep.

His bedroom was at the back of the workshop house, and the wall at the head of his bed was shared with the kitchen of Su Ji. It was a thin wall, old plaster over lath, and he had learned its voices over twenty-nine years: the clink of the big mixing bowl at five in the morning, the muffled hum of an old opera tune, the soft thump of a rolling pin. For eight years the sounds had been Grandma Su's alone. This week there had been another. A lighter step. A cupboard door that squeaked and was shut with a whispered ow. Once, at two in the morning, the rattle of a whisk in a bowl, rapid and furious, going on for a very long time.

He had not asked himself what she was making.

Tonight the wall was silent, and the rain was not.

He thought about the three days. He thought about the gate at the banquet, and the four sentences they had managed to exchange there. She had turned around with her eyes very wide, and he had said, because his mind had gone blank, "There's rain forecast for Thursday," and she had said, "I know," and he had said, "The tarp's holding," and she had said, "Thank you," and then there had been a silence so awkward that a passing duck had seemed to slow down to enjoy it. He had walked home with his ears burning. He was twenty-nine years old. He had once carried a four-hundred-pound beam up a ladder without breaking a sweat.

The rain thickened.

It will hold, he told the ceiling. I fixed it. It's a good tarp.

He had known it was not a good tarp since the afternoon he put it up.

Chengyan sat up, swung his feet to the cold floor, and listened. Somewhere beyond the wall, very faint, he heard it: tink. Then a pause. Then tink, tink, tink, faster, and a hollow slap as of water meeting a surface it had not been expecting.

He was already reaching for his trousers.

I'll only look, he told himself, hopping on one leg, dragging a sweater over his head. I'll check the north slope and come straight back. It's not for her. It's for the old lady. Seventy-four, she shouldn't be up there. I'd do it for anyone.

This was, he supposed, technically true, in the way that it was technically true that a person might do a very large favour for a stranger at one in the morning in the pouring rain with a forty-foot ladder.

The ladder was where he always kept it, hung along the side wall of the workshop on two iron hooks. He took it down by himself, quietly, one hand over the rungs so they would not knock. The rain struck his face as he carried it across the yard, cold and clean, and by the time he had propped it against the eaves of Su Ji he was already wet to the skin. He put his boot on the first rung and stopped.

The courtyard wall had a door in it, an old green one that no one had locked in forty years. Beyond it he could hear the chime of water in a bucket. He counted: one bucket. Two. Three.

He climbed.

The tiles were slick as fish. He went up on his toes and fingers the way he had done since he was fifteen, and when he reached the ridge he crouched there with the rain running off his chin and looked down the north slope, and his stomach sank.

The blue tarpaulin had torn.

It had gone along the seam where he had overlapped it, and a long ragged flap hung down into the gutter like a dead tongue. Beneath it, where the rafters met the wall, the wood was dark with wet, and he could see a thin steady stream of water sliding straight down into the gap. It was worse than he had thought. It was much worse than he had said to her. The end of the beam over the kitchen, the rotted end, was slowly drinking the sky.

"Fine," he said aloud, between his teeth. "Fine. All right."

He unrolled the spare tarp from where he had tied it to his belt, and began to work.

He had been up there for perhaps ten minutes, one knee pinned against the slope and both hands fighting a sheet of canvas that wanted very badly to be a sail, when a thin beam of light swept across the roof and fixed on him.

"Gu Chengyan!"

He froze.

"What do you think you are doing?"

He looked down. In the courtyard, standing beside the jasmine pot in a yellow rain jacket two sizes too large, with a torch in one hand and an enormous black umbrella in the other, stood Su Wenxi. The umbrella was doing nothing for her. The rain was coming at her sideways. Her hair had come down on one side and stuck to her cheek, and she was glaring up at him with an expression of such pure outrage that, for one wild second, he almost laughed.

"Checking the roof," he said.

"At one in the morning! In this!"

"It's leaking."

"I know it's leaking! I live here! I have a basin! I have four basins! I have a system!" The torch beam wobbled. "Come down. Come down this instant, you'll fall and break your neck, and then I'll have to explain it to your grandfather, and he'll be disappointed in me, and I already have enough people in this town who are disappointed in me."

"Nobody is disappointed in you."

"That is not the point!"

"It'll take ten minutes," said Chengyan.

"It will take ten minutes and then you'll be dead!"

"It's a very gentle slope."

"It is not a gentle slope! It is a, a wet slope! Why are you so stubborn? Come down!"

"No."

The word hung there, flat and calm, in the roar of the rain.

He looked down at her face turned up to him in the torchlight, her mouth open, her eyes blazing, and something in him, something that had been tightly rolled for eight years like a spring in a clock, shifted by a fraction of a turn. He had not said no to her in a long time. He had not said anything to her at all in a long time. It felt like picking up a tool he had not used for years and finding that it still fit his hand.

Wenxi stared at him.

Then she did something he had absolutely not expected. She threw the umbrella down on the flagstones, tucked the torch under her arm, hitched up the oversize jacket, and put her foot on the ladder.

"What are you doing?"

"Helping."

"You're not helping. Get down."

"You said no. I said no. We're both saying no, and the water's still coming in." She climbed with her chin set, and he had to give her this: she climbed like a girl who had once spent every summer scaling the willow, quick and sure, with only a little muttering. "Where do you want me?"

"Nowhere. Go back down."

"Where do you want me, Chengyan."

He stared at her. She had reached the top rung and was crouched at the lip of the eaves, wet, furious, wild-haired, holding the torch like a weapon. He opened his mouth to argue, and the wind took the loose edge of the tarp and snapped it across both their faces.

"Hold the corner," he said, thickly.

"Which corner?"

"That one. No. The other one."

She lunged. He lunged to guide her. They met in the middle, shoulder against shoulder, hip against hip, and for a second the whole slope tilted and her hand closed hard over his wrist and his arm went round her waist, and he felt her whole slight weight press into his chest, her breath warm and fast on his jaw.

Neither of them moved.

The rain beat on the tiles around them. The torch had rolled into the gutter and lay there with its beam pointed at the sky, throwing a cone of silver through the falling water. In its glow he could see every drop on her lashes. She was looking at him from about four inches away, and there was no anger in her face anymore, nor any smile, only the most naked surprise, as if she had been walking down a road for eight years and had just come round a bend and found him standing in it.

"You've got a scar," she said stupidly. "On your chin."

"Mm."

"It wasn't there."

"No."

Her fingers tightened, very slightly, on his wrist. His heart, which had been behaving itself with great discipline for most of a decade, began to hammer. He was suddenly, desperately aware of the size of his hands.

Then the wind came again.

It came in a long howling gust straight up the slope, and the spare tarp, which neither of them had been holding, filled like a spinnaker and tore itself out of the knots. It rose into the air, flapped once with enormous dignity, and sailed away over the rooftops of Sixth Alley into the dark.

They watched it go.

"That," said Wenxi, in a very small voice, "was your good tarp."

"That was the spare."

"It looked expensive."

"It was."

A tiny sound escaped her. It was a squeak, hardly a sound at all, the noise of a person trying very hard not to laugh in a church. She clamped her lips together. Her shoulders began to shake. And Chengyan, looking at the blank sky where eight hundred yuan of waterproof canvas had just flown out of his life, felt something rise up in his own chest like a bubble in a pot and break.

He laughed.

It came out rusty and startled, cracked in the middle like a plank left too long in the sun. He had not laughed out loud in so long that for a second he did not recognise the sound. It simply came, helpless and warm, and he could not stop it. He leaned his forehead against his arm and laughed in the rain, on a roof, at one in the morning, with Su Wenxi laughing beside him until she had to hold on to the chimney to keep from sliding off.

"Your face," she gasped. "Oh, my goodness, your face."

"I liked that tarp."

"I know you did. It was a lovely tarp. It's off to see the world." She wiped her eyes with a wet sleeve. "It's going to land on the Wei sisters' washing line and they'll think it's a gift."

He laughed again, helplessly, and when he looked up, she was watching him with a strange soft expression, her mouth still curved but her eyes gone quiet and wide.

"There you are," she said.

He stopped laughing.

It was the thing Tang Rui had said to her that afternoon, though he could not know that. He only knew that her voice had gone low and unguarded and gentle, and the rain was a curtain around them, and there was a feeling in his chest like a hand pressed against a door.

"We should get down," he said roughly.

"Yes," said Wenxi. "We should."

They got down. They were very careful about it. Neither of them spoke, and neither of them looked at the other, and when his foot touched the flagstones he found that his hands were not quite steady on the rungs.

The kitchen of Su Ji was bright and warm and smelled of ginger.

He did not remember agreeing to come in. He remembered only that the back door had been standing open, a yellow wedge of light cut into the dark, and that a small voice from inside had said, quite calmly, "Don't drip on the floor, take your boots off," and that his feet had done as they were told.

Grandma Su stood at the stove in her quilted dressing gown, her hair in its night plait, stirring a small copper pot. She did not look surprised. She did not look at all as though she had been woken by the sound of two young people shouting on her roof at one in the morning. She looked, in fact, like a woman who had been sitting up with the pot on the simmer for exactly this purpose.

"Sit," she said.

They sat. There were two stools drawn up at the corner of the work table, side by side, a good deal closer together than the table required. Wenxi opened her mouth.

"Sit," said Grandma again, and she poured two bowls of ginger tea, thick and pale gold and steaming, and set them down before them. A small pile of brown sugar lumps sat on a saucer between the bowls. She put two clean towels on the table, one beside each of them, and then she did the most extraordinary thing.

She yawned. She patted her mouth with her hand, in a delicate and unconvincing way, and said, "My, I am sleepy. I'll just rest my eyes for a moment," and lowered herself into the old rattan chair beside the stove, folded her hands over her stomach, and closed them.

Within ten seconds she was snoring.

It was an excellent snore. It rose and fell with great regularity. It was the snore of a person who had practised.

Chengyan looked at Wenxi. Wenxi looked at Chengyan. A droplet fell from the end of her nose into her tea.

"She's not asleep," he murmured.

"Not even slightly."

"She's been awake since the first drop."

"Since before the first drop. She's been up for an hour, I could hear her pot." Wenxi lifted her bowl in both hands and drank. A little colour came back into her face. "I can't believe her. She's eighty years of cunning in a seventy-four-year-old woman."

"Seventy-four."

"I know. It's even more impressive."

He found the corner of his mouth tugging up and let it. The tea was strong and sweet and fiery, and as it went down it spread out through his chest in a long slow warmth, and for a while there was no sound in the kitchen but the rain on the window and Grandma Su's tireless snore.

"I'm sorry," Wenxi said eventually, to her bowl. "About the tarp. And the ladder. And, you know, shouting."

"I should have told you how bad it was."

"You should have," she agreed. "I'd have been very cross."

"I know."

She glanced at him sideways. "Is it really that bad?"

He thought about lying. It was the kind thing, the careful thing, the thing a stranger would have done. Instead he said, "The end of the beam is rotten. If it goes in a storm, the north slope comes down into the kitchen."

She was silent for a moment. "How long?"

"Properly? A month. Maybe two."

"And the deposit is due at the end of this one."

"I'll start with the beam," said Chengyan. "I can do that before the deposit. It won't be on the bill."

"Chengyan."

"It's one beam."

"It's your time. It's your wood."

"It's her roof," he said, and then, because it was one in the morning and he was warm for the first time in three days, and perhaps because of the ginger, he said, much more quietly, "It's your roof."

Wenxi did not answer. When he looked over, she had gone very still, with the towel halfway to her hair.

Then she lifted it and began to dry herself in short, brisk, slightly embarrassed strokes, rubbing her scalp until her hair stood up in damp black spikes, and there was nothing, absolutely nothing, in the whole of the kitchen of Su Ji that he could safely look at except her.

She had pulled off the oversized yellow jacket and hung it on the back of the stool. Under it she wore an old grey sleep shirt that read, in cracked letters, SWEET DREAMS, and her feet were bare on the cold tiles, and her hair had come entirely loose from its band. A drop of water ran down her temple. She wiped it away with the back of her wrist, exactly as she had done at the age of ten, after a bowl of hot soup, and caught him looking, and smiled at him, a small tired unguarded smile, with the dimple.

Not the bright one. Not the one she had been giving everyone else in the street for a week. This one was crooked, and she did not know she was wearing it.

Chengyan looked down at his hands round the bowl.

He had done everything correctly. He had been polite for three days. He had been cold. He had been reasonable, and professional, and entirely at a distance, in a way that his grandfather would have called mule-headed and the whole of Sixth Alley would have called a performance. He had built it up board by board, the way a man builds a wall, for eight years, and it had held very well. It had held through the first sight of her on the roof and the long silence at the gate and the whole bright foolish business of the banquet.

And it had taken one wet laugh and a pair of bare feet to bring it down.

She was still smiling. She was rubbing her hair with one of Grandma's towels, the old thin blue one with the darned corner, and in the warm yellow light, in the smell of ginger and rain and flour, she looked exactly as she had looked at sixteen, sitting on the end of his workbench with her legs swinging and a sketchbook in her lap, telling him that one day she was going to make a cake the size of a house.

And I'm going to build the door you walk through, he had said. I'll make it wide enough.

He had been nineteen. He had said it so quietly that she had not heard.

Chengyan drank the rest of his tea. It had gone cool. He set the bowl down carefully, because his hand was not entirely to be trusted, and listened to Grandma Su's snore, and the rain, and the quiet sound of a woman drying her hair beside him.

It's breaking again, he thought, with the dull exact calm of a carpenter who has watched a crack run through a good plank and knows precisely where it will go.

It's going again, and I let it.

On the rattan chair by the stove, Grandma Su's snore faltered, just for a moment, and resumed.