Alli had always wanted to be a twin so when she found an old, black coin by the bridge one afternoon she closed her eyes tightly and wished she had a twin sister.

For a moment Alli felt suspended in black space, with a great wind rushing past her head.

“Hey Alli,” said a familiar voice, “are you and Emma going to Rob’s party?”

Alli opened her eyes and saw Carina, her best friend, sitting on the parapet next to an identical copy of herself. She stared, open mouthed, at the apparition.

“Because I asked you both yesterday and you still haven’t told me,” continued Carina, “and I don’t want to go by myself.”

“We’re going,” said the mirror image Alli, jumping off the wall, “come on, Carina, let’s get some hot chocolate.”

Alli stood motionless, staring at the vision of herself. It was impossible, yet here was this twin, looking perfectly alive and normal with Carina acting as if nothing strange had happened.

“OK,” Carina agreed, “but don’t talk all morning, Emma, you know what you’re like when you get going.”

Alli nodded, wondering what Emma was like when she got going, and what her parents were they going to say when this carbon copy of Alli turned up at the house. She was even wearing clothes like Alli; the same faded jeans, but with a tear on the pocket, and a cream sweatshirt, just like the one that Alli had wanted to buy last week.

Carina had run ahead to catch up with Emma and the two girls were now walking with linked arms. Alli felt a sudden pang of jealousy. How could this Emma person just appear, wearing the sweatshirt that Alli wanted, and turn her world upside down? She had wished for a twin sister; now that she had one it was not what she expected.

Then Emma turned around and held her hand out and Alli felt a surge of sisterly affection as the three girls marched into the café.

“I prefer the whipped strawberry shake we had yesterday,” Emma said, “don’t you Alli?”

Alli shrugged. She’d had a strawberry shake with Carina the day before, but nobody else had been there.

“You’re very quiet today, Alli,” Carina said, blowing on her hot chocolate. Emma had chosen the same topping as Alli and had even reached for the same cookie just as Alli stretched her hand out to the plate. It was uncanny.

“I’m just thinking,” she replied.

“Remember that time you were thinking so hard that you fell off your bike into the ditch?” Emma asked.

Alli was surprised. She did remember that day; concentrating on pushing the pedals, first with one foot then the other, she had not noticed the road curving until she had ridden head first into the ditch. But Emma was not there – how could she have been, if she had only just appeared?

Alli thought back to the scene on the bicycle and now, in the distant recesses of her memory she could see another small figure in the background, with an identical bike, her little feet pushing her own little pedals.

Alli shuddered and closed her eyes, but it was the same with all her memories. Where once there was just herself now there were two little girls, splashing each other in the pool, building two sandcastles at the beach, sharing a sandwich on the first day of school.

Alli pushed her hot chocolate away.

“I don’t feel well; I think I’ll go home.”

“See you at the party on Sunday,” said Carina.

Alli nodded and left the cafe, walking slowly along the path. She studied the grass and the hedge carefully to see if they had changed but they appeared to be the same old blades and the same old leaves and twigs. So what had changed?

A big thump on her back was her answer.

“Hey, Alli,” her duplicate said, “you’ve been acting strange today. Are you OK?”

Alli wondered what to say. How do you tell somebody that they did not exist an hour ago, that they were created by a wish? Yet Emma was standing in front of her, very definitely existing, and becoming part of her life. Alli looked up at her new twin. How much of herself was in there?

Carina was right; Emma did talk a lot, which was a relief because Alli just had to listen. Emma chattered about people they both knew, and what she thought of chemistry class and whether they should wear their red sweaters to the party. By the time they reached the house Alli really did feel as if this newcomer had been around for ever.

At home Alli noticed the changes at once. Not big, glaring differences, but two photographs instead of one, two pairs of shoes thrown outside the door, two bicycles in the shed.

Alli slowly pushed open the door to her bedroom and was surprised to find a second bed at the other side of the room, a second bookcase, and double the usual quantity of clothes on the floor. Alli lay down on her bed and stared at the tiny fluorescent stars on the ceiling above her. The ceiling above the other bed was covered in coloured petals and Alli remembered trying to decide between the petals and the stars. Was Emma just a collection of her discarded choices?

Alli had a difficult week adjusting to the new arrival but none of her friends or family thought it the least bit strange that there were now two of them. Alli wondered why the magic had not included a larger car, as it obviously stretched to beds and bikes and this thought made her giggle as they got ready for the party.

“What’s so funny?” asked Emma.

“Oh nothing,” said Alli, “you wouldn’t understand.”

Emma looked hurt and Alli felt sorry; she could not help liking her new twin, who was just like herself, but yet she could not feel a bond with this person, not like the bond twins were supposed to have. Emma, it seemed, did feel a special bond, or at least, had memories of enjoying a bond with her twin right up until the time at the bridge.

“Just what happened to you at the bridge last Saturday?” Emma asked, holding two t-shirts in front of the mirror.

Alli was becoming increasingly annoyed that Emma kept choosing clothes that she herself wanted to wear to the party. There was no way she was going to the party in identical clothes – that was just too silly, even though apparently most of their friends could tell them apart. But it did seem unfair that Emma had first choice; after all, she, Alli, had been there first, hadn’t she?

“Nothing,” Alli scowled. She threw herself on her bed clutching both red sweaters, to make sure that Emma did not take one.

“Maybe I’ll wear these jeans,” said Emma, picking up a crumpled pair from the floor. Alli said nothing. She would wait until Emma was dressed and then wear something completely different, just to make a point. Emma was fussing with her hair, twisting it the same way that Alli did and now looking for a hair tie. She reached into the pocket of the jeans, pulled out something and looked at it.

“Hey, what’s this?” she asked, “I haven’t seen it before.”

Alli glanced over and saw that Emma was holding the funny black coin she had found by the bridge.

“Hey, that’s mine,” she said, leaping up, “give it back!”

Emma shrank backwards.

“No need to get wound up, I’m just looking. And what’s come over you, anyway? You’ve been biting my head off all week and you never tell me anything any more.”

“I’m just in a mood, okay? I don’t know what’s wrong. Anyway, that’s mine, so can I have it, please?”

“Nah, ah. We share, remember, so I get to have this for a while. What’s so special about it – did somebody give it to you? Is that it – you’re in love and you don’t want to tell me?”

Alli reached out for the coin but Emma was too quick for her and jumped aside.

“Give it back, now!” Alli cried.

“You know, you’re not yourself these days,” said Emma, sounding angry for the first time, “something’s definitely happened to you, Alli. In fact you’ve become a pain in the side.”

Emma held the coin up in the air, just out of reach of Alli’s frantically waving hand.

“I never thought I’d say this, but sometimes I wish I didn’t have a twin.”

Alli suddenly felt herself suspended in black space with a great wind rushing past her head.

The door opened and Carina came into the room.

“Come on Emma, or we’ll be late.”

Emma dropped the coin she was holding, wondering briefly where it had come from and grabbed her red sweater from the bed.

“OK, I’m ready. Let’s go.