Erik stopped in front of the shop in Christianshavn to look at the bird in the cage. It had caught his eye as soon as he turned into the road, impossibly exotic on its black velvet cushion, lit by a single spotlight. There was nothing for it but to dismount from his bicycle and stare, his face bathed in the soft yellow glow from the window.

The cage was golden with a domed roof and a square base decorated with a garland relief. Inside, on a perch wrapped in silk flowers, sat a stuffed bird, dull brown with a grey chest and rusty tail feathers.

Erik looked up and down the street. No one else was stopping or giving the window a second glance. The bird seemed to be looking directly at him, its head cocked to one side, its beady eyes fixing him with an imploring stare.

When he got to the office, he found that he could not concentrate on anything. In meetings, his mind drifted constantly to the bird. As soon as he could, he cycled back to the shop, relieved to find it still there in the window. Standing in the dark, with the bird’s huge eyes on him, he felt a quickening in his blood that he could not account for.

He thought how he should like to polish the cage till it shone, remove the faded silk flowers and replace them gently with sprigs of cherry blossom from the park opposite his apartment. He saw himself reaching in and cupping the bird gently in one hand and, in his fantasy, its tiny heart fluttered and its beak scratched his palm.

He had never bought anything for himself that wasn’t in some way practical, but he knew, with a certainty that grew day by day, that he wanted the bird in the cage. He even thought of the perfect place for it in his apartment: the little window nook with the round mahogany table that had been his mother’s. If the bird were his, he would pull up a chair and sit there all day and look at it as the sunlight passed through the bars of the cage and painted patterns across the floor.

The next day, he parked his bicycle by the shop, removed his helmet and smoothed down his hair. An old-fashioned bell rang when he entered, his hand moist and trembling on the door handle.

The shop was warm and smelled pleasantly of cigars and old wood. A grandfather clock was ticking loudly, drowning out the noises from the street outside. Erik stood for a while, adjusting to the dim light and the distinct sensation of having stepped outside of time.

The few objects in the shop were displayed on plinths of varying height, each brightly lit. He saw a music box with a twirling ballerina in a pink dress, a porcelain vase decorated with flowers and dragons, a tall ship with its sails unfurled inside a bottle.

‘May I help you?’

The shopkeeper startled him: an old woman, tiny and stooped in a knitted black dress with thick grey stockings and black lace-up shoes. She looked up at him shrewdly, reminding him of the little brown bird with its cocked head.

Erik straightened his back, cleared his throat and spoke as commandingly as he could.

‘The bird in the cage, in the window. Can I see it?’

The shopkeeper smiled indulgently. As she pulled back a velvet curtain and leant slowly into the window display, Erik fought an urge to push her aside and do it himself.

But then he saw something he had not noticed before: a large brass key protruding from the base of the cage.

‘It’s an automaton,’ the shopkeeper said, following his gaze. ‘A mechanical nightingale made by master craftsmen in Paris one hundred and fifty years ago. They used the feathers and beak from a real bird. Watch.’

She turned the key a number of times and let go. The bird began to nod its head and turn this way and that, singing trills that sounded surprisingly real, with only the faintest rhythmical clanging of the cogs below.

They stood in silence and listened. Erik thought it was the most astonishingly beautiful sound he had heard in his life.

The shopkeeper spoke softly, as though imparting a secret. ‘The nightingale is celebrated for its song. It’s the virtuoso of birds – few can match its range. You are familiar with the Hans Christian Andersen fairy tale?’

Erik nodded. He remembered his mother reading the story to him when he was a boy. As the shopkeeper retold it, his eyes never left the bird.

‘When the emperor of China hears of the plain nightingale with the beautiful voice, he orders it to be brought to his palace. But soon his head is turned by a wind-up bird studded with jewels, sent to him by the emperor of Japan. While no one is looking, the real nightingale flies out of a window and returns to the forest. The emperor is angry and bans the bird from his kingdom. Years later, when the artificial songbird has broken, and the emperor lies dying, the nightingale flies back to the palace and sits on the windowsill and sings. Even Death is moved by the song, which makes him long for his own garden and leave the emperor’s bed. The emperor lives and the nightingale is free.’

‘Could you make it sing one more time?’ Erik said, his voice croaky and thick.

As the bird sang again, twisting and turning its little head, his eyes filled with tears.

The birdcage did not have a price tag on it. There were no prices on any of the items in the shop, come to think of it.

‘How much is it?’ Erik said.

The shopkeeper looked at him for a while before replying. When she spoke, the price she gave was almost the same as the new bicycle Erik had planned to buy. He was astonished.

‘How can an old thing made of a little brass and few feathers and cogs cost so much money?’

The shopkeeper gestured around the room. ‘The value of these objects hinges upon the desire of customers to own them, not the materials they were made from. If someone wants something enough, no price is too high, and they will stop at nothing to get it.’

‘Rubbish,’ Erik said. ‘People have more sense than that.’

The shopkeeper said nothing in reply, merely smiled at him and waited.

Erik thought, I want the bird, but I really need a new bicycle. I don’t need the bird.

A shadow of these deliberations must have crept over his face, because before he knew it, the shopkeeper had gently picked up the birdcage and returned it to the window. Not knowing what else to do, Erik thanked her, left the shop and went home.

When he woke the next morning, he knew that he had been wrong. He needed the bird more than he needed a new bicycle. A few minutes after nine, he was on his way to Christianshavn, pedalling hard.

He almost fell through the door to the shop.

‘I have changed my mind,’ he shouted, holding up his wallet. ‘Please can I buy it, the bird in the cage?’

‘Certainly.’

The shopkeeper did not seem surprised to see him. She went over to the window with no particular urgency, leant into the display and picked up the cage. Then she put it on the counter and rang it up on an old cash register Erik hadn’t noticed before.

When the price came up, Erik thought there must be some mistake. The price was higher than the price of the new bicycle; it was almost as much as the new bathroom he had planned to buy.

‘That’s not the price you told me yesterday!’

‘No,’ the shopkeeper said. ‘You didn’t want it as much yesterday as you do today.’

Erik left without thanking her and walked all the way to the office, too miserable to even get on his bicycle.

That evening when he got home, the apartment felt even emptier than usual. He pulled up a chair and sat and stared at the round mahogany table where he had imagined putting the birdcage. It was as if it had always been there, but was now missing, leaving an empty space that could not be filled with anything.

Lying in bed that night, he resolved to go back to the shop the next morning and pay whatever the old woman asked of him. He fell asleep relieved, his mind made up.

When he stepped through the door to the shop, he was whistling cheerfully, stepping aside to make way for another man just leaving with a large box tied up with string.

‘It’s all right,’ he said to the woman. ‘Whatever the price is today, I will pay it. I want that bird more than anything. I am certain of that now.’

‘I see,’ the shopkeeper said, smiling that incongruous smile of hers, but she didn’t move from behind the counter. ‘I am afraid I must disappoint you. I just sold it to that gentleman who left the shop as you came in.’

Erik felt his knees give. He had to put a hand on the counter to stop himself from falling over. In his rush to get to the shop, he had not noticed the cage was missing from the window display.

‘How could you?’ he heard himself say. ‘That bird was mine.’

The shopkeeper shrugged. ‘The other gentleman was willing to pay what I asked. He obviously wanted the bird more than you did.’

Erik felt his hands bunch into fists. ‘No one wants that bird more than I do,’ he said.

The shopkeeper watched him passively as he turned around and tore open the door, rattling the bell.

He ran up the street, propelled by a force of anger he had never known before. He wasn’t really there, but for his feet pounding the pavement and his fists swinging like clubs from his elbows. He saw nothing but the man up ahead, carrying the birdcage away. The long years stretched out before him, empty years of cycling to and from work and never again hearing the song of the nightingale.

He caught up with the man by the canal. He was clutching the box to his chest and shaking his head, as Erik stepped in front of him. The man’s lips were moving, but Erik could only hear his own laboured breathing and the blood rushing in his ears. He grabbed at the string and tried to pull the box away from the man, feeling the birdcage moving inside. The man bared his teeth and tried to shift his grip on the string, but as he did so the box slipped from his hands and fell onto the cobbles between them; there was a loud rattling nose and a single heart-rending tweet could be heard from inside.

Something dark descended on Erik’s vision then. A roar filled his head and he saw his hands dart out from his body like pistons, shoving at the man’s chest. Now the man was stumbling, his arms were flailing. Then he was gone, over the edge and into the canal with a loud splash, and Erik was kneeling on the cobbles, rocking back and forth with the nightingale in his arms.

A woman’s scream woke him. He felt strong arms pinning him to the ground, heard himself say, again and again: ‘I don’t know what came over me. I don’t know what happened.’

By the time the police got the man out of the black canal water, he was dead. He had hit his head on the edge of a boat, fracturing his skull.

They put Erik in handcuffs and made him sit in the back of the police car. An officer sat next to him, holding the cardboard box in his lap as the car began to edge its way through the crowd of onlookers.

‘That box is mine,’ Erik said. ‘Will they let me keep it in prison?’

The officer shook his head. ‘If and when you are convicted, it will go into storage for safekeeping until you are released.’

Good, Erik thought and he saw himself, years from now, reaching into the squashed and dented cardboard box, gently lifting out the birdcage and stroking the little bird, and he felt calmer.

When they passed the shop window, he noticed that the birdcage had been replaced with a white rocking horse, its shiny grey mane caught in the light from a single spotlamp.

Erik couldn’t help but admire it, and he turned his head to look out of the rear window of the police car. As he did so, he saw the shopkeeper standing behind the door, looking at him, seeing everything, and he wasn’t sure, but he thought the old woman might have been smiling.