The old black key felt colder than any of the others. She pushed it into the keyhole. It turned smoothly, with a satisfying clunk.

Coraline stopped and listened. She knew she was doing something wrong, and she was trying to listen for her mother coming back, but she heard nothing. Then Coraline put her hand on the doorknob and turned it; and, finally, she opened the door.

It opened on to a dark hallway. The bricks had gone, as if they'd never been there. There was a cold, musty smell coming through the open doorway: it smelled like something very old and very slow.

Coraline went through the door.

She wondered what the empty flat would be like-if that was where the corridor led.

Coraline walked down the corridor uneasily. There was something very familiar about it.

The carpet beneath her feet was the same carpet they had in their flat. The wallpaper was the same wallpaper they had. The picture hanging in the hall was the same that they had hanging in their hallway at home.

She knew where she was: she was in her own home. She hadn't left.

She shook her head, confused.

She stared at the picture hanging on the wall: no, it wasn't exactly the same. The picture they had in their own hallway showed a boy in old-fashioned clothes staring at some bubbles. But now the expression on his face was different-he was looking at the bubbles as if he was planning to do something very nasty indeed to them. And there was something peculiar about his eyes.

Coraline stared at his eyes, trying to work out what exactly was different.

She almost had it when somebody said, "Coraline?"

It sounded like her mother. Coraline went into the kitchen, where the voice had come from. A woman stood in the kitchen with her back to Coraline. She looked a little like Coraline's mother. Only…

Only her skin was white as paper.

Only she was taller and thinner.

Only her fingers were too long, and they never stopped moving, and her dark-red fingernails were curved and sharp.

"Coraline?" the woman said. "Is that you?"

And then she turned round. Her eyes were big black buttons.

"Lunchtime, Coraline," said the woman.

"Who are you?" asked Coraline.

"I'm your other mother," said the woman. "Go and tell your other father that lunch is ready." She opened the door of the oven. Suddenly Coraline realised how hungry she was. It smelled wonderful. "Well, go on."

Coraline went down the hall, to where her father's study was. She opened the door. There was a man in there, sitting at the keyboard, with his back to her. "Hello," said Coraline. "I-I mean, she said to say that lunch is ready."

The man turned round.

His eyes were buttons-big and black and shiny.

"Hello, Coraline," he said. "I'm starving."

He got up and went with her into the kitchen. They sat at the kitchen table and Coraline's other mother brought them lunch. A huge, golden-brown roasted chicken, fried potatoes, tiny green peas. Coraline shovelled the food into her mouth. It tasted wonderful.

"We've been waiting for you for a long time," said Coraline's other father.

"For me?"

"Yes," said the other mother. "It wasn't the same here without you. But we knew you'd arrive one day, and then we could be a proper family. Would you like some more chicken?"

It was the best chicken that Coraline had ever eaten. Her mother sometimes made chicken, but it was always out of packets, or frozen, and was very dry, and it never tasted of anything. When Coraline's father cooked chicken he bought real chicken, but he did strange things to it, like stewing it in wine, or stuffing it with prunes, or baking it in pastry, and Coraline would always refuse to touch it on principle.

She took some more chicken.

"I didn't know I had another mother," said Coraline cautiously.

"Of course you do. Everyone does," said the other mother, her black-button eyes gleaming. "After lunch I thought you might like to play in your room with the rats."

"The rats?"

"From upstairs."

Coraline had never seen a rat, except on television. She was quite looking forward to it. This was turning out to be a very interesting day after all.

After lunch her other parents did the washing-up, and Coraline went down the hall to her other bedroom.

It was different from her bedroom at home. For a start it was painted in an off-putting shade of green and a peculiar shade of pink.

Coraline decided that she wouldn't want to have to sleep in there; but that the colour scheme was an awful lot more interesting than the one in her own bedroom.

There were all sorts of remarkable things in there she'd never seen before: wind-up angels that fluttered around the bedroom like startled sparrows; books with pictures that writhed and crawled and shimmered; little dinosaur skulls that chattered their teeth as she passed. A whole toybox filled with wonderful toys.

This is more like it, thought Coraline. She looked out of the window. Outside, the view was the same one she saw from her own bedroom: trees, fields and, beyond them, on the horizon, distant purple hills.

Something black scurried across the floor and vanished under the bed. Coraline got down on her knees and looked under the bed. Fifty little red eyes stared back at her.

"Hello," said Coraline. "Are you the rats?"

They came out from under the bed, blinking their eyes in the light. They had short, soot-black fur, little red eyes, pink paws like tiny hands, and pink, hairless tails like long, smooth worms.

"Can you talk?" she asked.

The largest, blackest of the rats shook its head. It had an unpleasant sort of smile, Coraline thought.

"Well," asked Coraline, "what do you do?"

The rats formed a circle.

Then they began to climb on top of each other, carefully but swiftly, until they had formed a pyramid with the largest rat at the top.

The rats began to sing, in high, whispery voices:

It wasn't a pretty song. Coraline was sure she'd heard it before, or something like it, although she was unable to remember exactly where.

Then the pyramid fell apart, and the rats scampered, fast and black, towards the door.

The other crazy old man upstairs was standing in the doorway, holding a tall black hat in his hands. The rats scampered up him, burrowing into his pockets, into his shirt, up his trouser-legs, down his neck.

The largest rat climbed on to the old man's shoulders, swung up on the long grey moustache, past the big black-button eyes, and on to the top of the man's head.

In seconds the only evidence that the rats were there at all were the restless lumps under the man's clothes, forever sliding from place to place across him; and there was still the largest rat, who stared down, with glittering red eyes, at Coraline from the man's head.

The old man put his hat on, and the last rat was gone.

"Hello, Coraline," said the other old man upstairs. "I heard you were here. It is time for the rats to have their dinner. But you can come up with me, if you like, and watch them feed."

There was something hungry in the old man's button eyes that made Coraline feel uncomfortable. "No, thank you," she said. "I'm going outside to explore."

The old man nodded, very slowly. Coraline could hear the rats whispering to each other, although she couldn't tell what they were saying.

She was not certain that she wanted to know what they were saying.

Her other parents stood in the kitchen doorway as she walked down the corridor, smiling identical smiles, and waving slowly. "Have a nice time outside," said her other mother.

"We'll just wait here for you to come back," said her other father.