It began with a dream. Ruth's sleeping life had always been more brilliantly plumaged then her waking life. She woke with an image of a woman, white-clad, shadowy under the leaves, one hand pushing open a door into a garden, the other held out towards her.

The dream haunted her. She felt she had seen the wall, the door, the falling fig vine, before. Trying to remember where, Ruth began to wander the streets of her childhood as she had not done in years, pushing through seed-laden grass to walk along the canal, scrambling up stony alleys verdant with weeds. That summer, the sun was so hot the pavement was sticky under her boots and the sky blazed with a blue of such intensity it seemed like the heart of a hissing flame.

At first it was this colour that demanded life, so Ruth painted the canvas blue. Whenever she saw the blue of her canvas she would feel the hole inside her satisfied. But it was so hot that summer they were all satisfied with little things at first. Mary, the eldest sister, was pleased with a skirt she bought for $20 at a sale. Zillah, the youngest, discovered the thrill of theft. Even their mother seemed a little less afraid.

Then the emptiness of her canvas infuriated Ruth. For blue demands drowning. Sitting on the floor in her bedroom, Ruth mixed the paint on her palette with her fingertips. Emerald-green, jade-green, lime-green, forest-green. Ruth painted a garden, with leaves and vines, shadows, a high wall. That night when she went to bed, her fingernails were thick with green as if she had been gardening.

Mary could not sleep. She lay in the stifling darkness, trying to unfurl her dreams so she too could slip into slumber with a smile. She could not. The dream was worn through, showing holes in the creases where she had unfolded it so many times.

Mary no longer styled her hair every morning, but dragged it back from her forehead. She gave her stilettos to her youngest sister, and laughed bitterly when she saw her practising walking. For Zillah had her own dreams, glossy as the pages of a magazine. Every day she reluctantly dressed in her ugly school uniform, her feet trapped in clumsy shoes. At night, though, Zillah outlined her eyes with charcoal and rubbed bronze into her cheekbones and gold into her eyelids. She draped her body in an orange scarf, and stared at herself in the mirror.

In the morning Zillah lay for a while in bed, watching her sister crouched before the canvas, smearing paint on to it with her fingers. Stretching, Zillah admired her own body in the mirror, before drifting into the kitchen for some orange juice. That was all she allowed herself for breakfast. She watched Mary and her mother eat their bran flakes with the tiniest curl of her upper lip. She would never be like them, Zillah told herself again. Never.

Zillah waited till her mother had left. She always caught the 8:04 bus. Ten minutes later Mary left, having lingered in the bathroom so she did not have to walk with her mother. She caught the 8:14 bus. Some time later Ruth would stomp out, dressed as usual in op-shop cast-offs, her backpack thumping on her back. She would scowl at Zillah, growl ‘Aren't you meant to be at school?’ and slam the door on her way out. Sometimes Zillah would follow her, curious to see where she went and what she did. Sometimes she would not bother. Zillah liked being home alone. Slowly, voluptuously, she would turn over her sisters’ things. She would outline her mouth with Mary's new lipstick, look through Ruth's art magazines, and rummage through their drawers in the hope of finding money.

Zillah would have liked to go through her mother's things too, but her mother locked her bedroom door. She locked every door. She kept her keys on a bristling ring that she carried with her always. At night, when she walked home from the bus stop, her mother carried the bunch of keys in her fist, clenched between her whitened knuckles like the barbs of a mace.

Ruth paid little attention to her mother and sisters. She thought they had rendered their lives provincial beige. She had her own plans, her own obsessions. At night she hunted the dream, and sometimes managed to net it. By day, she hunted the memory. The old door in a high sandstone wall, the falling fig vine, light gleaming out through leaves. Ruth had seen it before, she knew. When she was a child. Before her father left one night, and was never seen again.

The door in the wall could not be too far away, Ruth thought. Fleetingly, she remembered running through darkness. Being afraid. Creeping along the wall. The door swinging open, light piercing the night, the delicate tracery of vine and leaf and fruit, green-black against the gold. The gentle swish of a white skirt against the stone. A cool hand held out.

Or had this been a dream, too? Ruth did not know. She was not sure it mattered.

She was in the grip of the painting like a fever. As soon as she woke each morning she would crouch before the canvas, seeing with bleary eyes all that was wrong. With the very tip of her littlest finger, Ruth would caress a leaf with an edging of gold. With a broad sweep of her palm she would stroke the flowing white shape of skirt, or delicately trace the oval face. She barely dared sketch in the arch of brow, the curve of lip, the shape of beckoning fingers. Slowly the painting became crowded. Wall. Door. Fig leaves. Woman in white. Three white lilies.

When Mary was a little girl, she had woken one night, hearing a rhythmic thump, thump, thump, like a doll's head hitting each step as it was dragged downstairs. Each thump was followed by a small squeak, as if the speaking mechanism in the doll had been broken. Then there was another great thump, much louder, somehow out of rhythm. Then only silence.

Mary crept to her bedroom door. All was quiet. She reached up, slowly turned the handle, and crawled out into the hall. She could hear someone breathing fast and uneven. Listening with every nerve in her body, Mary felt along the floor with her hand. She did not know what she was looking for. A broken doll? Her little sister, alone and lost in the hall? Ruth went wandering in the night sometimes. Sleepwalking, her father explained, when he brought her back to bed. It was dangerous to wake a sleepwalker, Mary knew. In case they got lost in their dreams.

Mary's hand touched something. Cloth. She felt along. Skin. Hair. Someone was lying curled on the floor of the hallway. Their face was cold and wet. ‘Go back to bed, honey,’ her mother said. Her voice was hoarse. ‘Go back to bed.’

Mary had gone back to bed. When she woke in the morning, it was to find the nails of one hand were black, as if she had been digging in dirt. Zillah slept in her cot, all tangled with sheets, but Ruth's bed was empty. When Mary walked down the hall, it was damp under her bare feet. Her mother was sitting at the table, her hands gripping a cold cup of coffee. She did not look up. Her face looked somehow wrong. The house was cold and dark and silent. All the doors and windows were shut tight.

‘Daddy's gone away,’ her mother said.

‘Where?’

Her mother shook her head. ‘I don't know.’

Zillah did not remember her father. He had left when she was only three. One day she had said to Ruth, ‘I wish our father was here!’

Ruth had said briefly, without meeting her eyes, ‘Just be glad he's not.’

‘But Mum treats me like a kid!’

‘Better than the way he would've treated you.’

Mary did not want to feel an affinity with her mother. Although they had lived together for twenty-one years, it had been without connection. Mary did not expect or want a bridge to be built between them.

So one hot day, listening to Zillah wishing her life away, she was surprised to share a look with her mother, a look that said enjoy your youth, dear, it'll pass all too soon. That day they walked to the bus stop together.

That night, Mary could not sleep. She felt like she was being suffocated by the heat, pressing on her face like a stinking pillow. She got up and wandered into the room that Ruth and Zillah shared. There, propped against the wall, was a huge canvas of a woman in white, fig vines and ivy coiling about her. In one hand, the woman held three white lilies; the other was held out beseechingly.

Mary stood and stared, amazed and confounded that her brusque young sister could paint something so mysterious and beautiful. She reached out one hand and touched the lilies wonderingly, then snatched her hand away, glancing round to make sure no one had seen her.

She did not sleep well. She was more conscious of the hole in her than ever before, the many absences that pitted her life. At lunchtime the next day, Mary did not go and sit in the square, glancing at her reflection in the shop windows, hoping one of the suave men in grey hurrying past would stop and speak to her. Instead, she began to walk. She walked swiftly through the city, growing uncomfortably hot, until she walked through the grand iron gates into the botanical gardens. Without embarrassment she stripped off her pantyhose, standing on the grass in her bare feet. She found a tree and lay in its shade, closing her eyes, smelling the green air.

When Mary woke, the shadows were lengthening. Her legs stung where they had been lying in the sun. She watched the gardeners digging under the trees, and fell to chatting with one. ‘I'd love to work here,’ she said enviously. ‘It's so beautiful.’

‘There's a job to be had in the gift shop,’ he told her. ‘You should apply.’

On her way back to the office, she bought a white lily in a pot from a florist's cart, and gave in her resignation before her manager even had time to ask where she had been. Indeed, he could have guessed, for her fingernails were green with leaf-mould.

Zillah liked to find out people's secrets. She read Mary's diary, and discovered Mary did not like to feel her mother's face growing over her own. She stared at Ruth's painting. In the evenings now, when Zillah dressed up in her crimson gown and her red lipstick, she no longer flirted with herself in the mirror but sat and stared at the reflection of the painting, staring into the woman's long, shadowed eyes.

Zillah began to follow Ruth more often, taking photographs of her sister as she prowled the streets of the suburb. Ruth was not easy to follow. She seemed to travel at random, catching buses as they drove past her, jumping off with no warning. The more difficult it was to shadow Ruth, the more absorbed Zillah became. She stopped hanging around with her school friends outside the cinemas, or pilfering anything her hand crossed. Her use of disguises became ever more elaborate, her skill at hiding in doorways more polished.

One evening, Ruth came home hot and morose. Zillah, lying on her bed pretending to do homework, watched surreptitiously but Ruth did nothing but sit cross-legged in front of her painting, staring at it. The room began to grow dim as the sunlight outside faded. Soon it was almost dark. Zillah had to reach out and flick on her bedside lamp to see her maths book.

Ruth shot her a scowling glance, then got up and went out. Zillah heard the front door slam. At once she followed. She watched from her mother's window as Ruth began to walk slowly, stumblingly, along the street, hands held out, eyes shut. Zillah had to wait some time before she dared slip out and follow. It was almost dark.

Suddenly, some way along the street, Ruth stopped, turning her face as if listening. Or smelling. Zillah shrank back into the shadows. She watched as Ruth turned and plunged into a gap between two old exhausted terrace houses. Her sister disappeared into darkness. Zillah hurried after.

In the gap was a narrow flight of old stone steps, hidden behind the thick trunk of a spreading frangipani tree. Ruth was climbing the steps, using her hands as if she were a small child. As Zillah followed her, she squashed fallen frangipani flowers under her feet. The sweet, heady smell filled the air.

The steps led to a road Zillah had never seen before, although she had lived in this suburb all her life. It was higher than all the houses around it, a cul-de-sac at the end of a steep, narrow street that climbed behind the untidy backyards of terraces. A high sandstone wall ran the width of the close. Beyond it was a house graced by a tall tower with a peaked roof, dark against the luminous sky. Trees crowded up against the wall, which was draped with some kind of vine. There was a wooden door in the wall.

Ruth had lifted away the falling vines and stood with her hands pressed against the door. She stood very still. Zillah waited in the shadows a long time, but nothing happened and so she shrugged and went home, nonplussed and frustrated, her curiosity sharper than ever.

The next morning when she woke, Ruth was crouched before her canvas. With quick, sure, swirling motions, she was painting an ornate black key in the open palm of the woman in white. Zillah could only stare and wonder.

Ruth woke the next morning with the key pressed into the palm of her hand. For the first time in her life she felt like leaping out of bed, singing, laughing out loud. Instead she thrust the key into the pocket of her jeans and hurried out, for once not stopping to stare at her painting. Zillah watched through half-closed lids.

Ruth went swimming. Only submerged in the cool fizziness of the sea could she quell her joy, her excitement, her trepidation. She dove deep down, to where the sand slid away into fathomless dark. She stayed down so long her body hurt with its craving for oxygen. When at last she crawled on to the sand, her lungs heaved and her legs shook. Still the bright hours stretched before her.

At last it was dusk. With the key secreted in her hand, Ruth slipped past the guardian frangipani tree and up the sweet-scented steps. The smell reminded her of summer, of childhood. It made the pit of her stomach twist with dread. Fragments of memory came to her. She hurried away from them, up the narrow stony steps, to the hidden cul-de-sac with its vine-hung wall. There, behind the thick fig-laden vines, was the old wooden door with a keyhole whose dimensions she had measured carefully with her fingers. She slid the key from the palm of her hand into the keyhole and, holding her breath, turned it. The locks rolled and clicked. The door sprang free.

Golden light sprang out, silhouetting leaf and tendril. Within was a tangled garden, sweetbriar and bougainvillea and ferns. A fountain gently tinkled. A woman stood there, ghostly-white, her face shadowed by vines. Zillah saw her long, pale hand reach out and silently draw Ruth within. The door shut behind her.

This time Zillah did not go home, bored. She prowled the cul-de-sac, pushing with all her strength against the door, trying to find some way to scale the wall, craning her neck to see more of the garden and house that lay within. All was hidden.

At last Zillah gave up and went back to bed. She woke much, much later at the sound of her sister's boots on the linoleum. It was almost dawn. She could see the look of joy and release on Ruth's face in the thin, grey light striking through the blinds. It made her angry.

Zillah waited until Ruth was asleep, her hand curled up under her cheek. Then Zillah slipped out of bed, and gently eased open her sister's hand, taking the key. Her sleeping sister was grubby and dishevelled. There were cobwebs in her hair.

Tiptoeing past the painting, Zillah felt the woman's eyes upon her. In a sudden blur of rage, she seized Ruth's painting knife and lashed again and again at the canvas. In seconds, the woman in white was reduced to dangling strips of paint-encrusted fabric. Zillah ran out of the room, the knife in one hand, the key in the other.

She stood for a moment in the hall, not sure which way to turn. If she opened the front door, she would wake her mother, she knew. So Zillah went quietly through the kitchen to the back door. One by one she unlocked the bolts. They were stiff. They had not been opened in a very long time. Outside a pure light was filling the sky, rickety fences and Hills hoists standing up stark and black. Their backyard was a stretch of rubble and weeds. There was a tin shed, its door sticky with cobwebs. Zillah used the knife to sweep them away, and found an old spade, its rusty metal still caked with ancient dirt. She chose a spot behind the shed, so no one could see where she had been digging, and drove the spade into the dry soil. She wanted to bury the key deep, deep, where no one would ever find it.

The spade struck something. Zillah bent, lifting the soil aside. Her heart suddenly slammed against her ribcage. There, gleaming whitely in the dimness, were the bones of a skeletal hand. Zillah stepped back, unable to breathe, black horror coursing through her. For a long while, she stood, staring, her hand pressed to her pounding heart. Then she gave one swift, surreptitious glance all around, bent, dropped the key down on the bones, and hurriedly shovelled soil back into the hole. She put the spade back in the shed, shut and locked and bolted the door behind her, and crept back into her own bed, where she lay, pretending to be asleep, her heart still hammering like she had been running a marathon.

There was black dirt under her fingernails.

Ruth jerked out of sleep, her breath harsh in her throat, knowing the key was gone. She had felt its absence in her dream. Although she ran as fast as she could in the darkness, branches had groped for her, roots had tripped her, ivy had strangled her throat. She cried out but the door was shut and though she tore at the wood with her fingers, it would not open, the garden was lost, all was lost.

Ruth stood staring at her ruined painting, looked down at her empty palm. Her mind refused to tell her what had happened. It was all so impossible. She went out into the early morning, magpies calling weirdly, kookaburras jeering. Past the frangipani, up the stone ladder, and so to the cul-de-sac. There was the wall, hung with vines and ivy, weeds sprouting from the cracks. Set in the wall was the massive old door. Vines grew right across it, garlanding the massive old keyhole, cobwebbed and rusting. It had not been opened in years.