He couldn't stop running. Even though his heartbeat was hammering in his ears and every inhalation burned in his throat, Felix couldn't slow down before he'd shut the front door behind him. And all the way there, he had to keep up an angry frown. Because if he didn't, he'd probably begin to cry. And he wouldn't do that. They were wrong about him at school. He really was tough. Just like Sarah.

Sarah...

As soon as he was inside, he collapsed against the wall, trying not to think about her. And then screamed when the door to the living room opened and Sarah looked down on him.

"Fe!" she cried, crouching down and grabbing his shoulders. "Are you okay? What happened?"

Felix pulled away, staring at his sister. "You're... here?" he squeaked.

"Yeah, silly." Sarah let out a short hard laugh. "Where did you think I'd be? Trick-or-treating? With what friends?"

"But you were... You were... with those other people..." Felix shook his head. "How did you even get here so quickly?"

"What people, Fe?" Sarah reached out to put her hand on his forehead. "What are you talking about? I've been home all day. I'm suspended, remember?"

"No..." Felix batted her hand away and swallowed his tears. "It was you. I recognise my own sister! You were in those posh clothes, with... with parents. I saw you and you acted like you couldn't hear me when I called. You just... walked away..." He quickly rubbed away a stubborn drop of water on his cheek.

"Oh Fe..." Sarah sat back, looking at him. "I don't know what happened, but... I would never treat you like that. It couldn't have been me you saw. Now please... Get up and come with me to the kitchen. I'll make us some cocoa."

Felix studied her a moment longer and then hesitantly got to his feet, unable to hide a sniffle as he took Sarah's hand.

Sarah led him to the table and told him to sit down. As she worked on the cocoa, she kept silent, wearing her thinking frown.

"You really haven't been out?" Felix asked eventually, when he could no longer bear the tense silence.

"Not even to get the mail," Sarah said, crossing her heart. "Are you sure it wasn't just someone who looked a bit like me? How close a look did you get?"

Felix frowned. "Her hair was different. And her clothes... You'd never wear that, not in a million years. But she had your face, Sarah! Your eyes, your nose, everything!"

"That's strange," Sarah said. "I suppose it was... I suppose it was my shadow twin!" She poured the steaming cocoa into two mugs and carried them over, sitting down across from Felix.

"Your what?" he asked, his eyes wide.

"My shadow twin." Sarah lowered her voice, smiling secretively. "Have you never heard about shadow twins? Everybody has one. You. Mrs S. Me..."

"I have a twin?" Felix repeated.

"Of course, Fe. But they can only be seen on Halloween. I'm a bit jealous that you got to see mine, actually. I'd like to have seen her too. You can learn a lot from your shadow twin, you know."

Felix frowned. "She was... posh. I think her clothes must've been expensive. And those people with her... Do you think those were her foster parents? Or her real ones, even?"

"I suppose they could be," Sarah said, sipping her cocoa, wincing and blowing on it. "You see... Shadow twins are you. But a different you. It's you the way you could have been if something different had happened to you. When you were very young. So maybe this shadow twin is me as I would have been if my parents had kept me. Or, as you say, me with a different family. I guess I will have to find her myself and ask her. If I ever wanted to know, that is."

"I guess she has the good life," Felix said with a sigh. "They really did look rich." He sipped his cocoa too and hummed.

"Being rich doesn't mean you have a good life," Sarah said firmly. "You should know that, Fe. And I can promise you that she does not have a better life than me. That is not possible."

Felix smiled a little. "Is being suspended that much fun?"

"When it means seeing more of you." Sarah smiled too. "Having you as my baby brother is the best life I could wish for. And tonight we're going to have such an awesome time. I found some old scary movies. So old they're not really scary anymore. And Mrs S left us some treats. From back home. Not that sugary crap they sell over here."

Felix grinned. "That sounds amazing!"

…

Two films and a lot of still rather sugary treats later, Felix was dozing off, snuggled against Sarah's shoulder. But suddenly a thought struck him and he opened his eyes.

"What do you think my shadow twin is like?" he asked, looking up at Sarah.

She thought for a moment. "I think he looks really really cute," she said, putting her arm around him. "But not quite as cute as you."

Felix giggled. "I wish I could meet him."

"Of course you do. But..." She lowered her voice dramatically. "Shadow twins can only be seen on Halloween and..." She checked her watch. "Sorry, Fe. Halloween is kinda over. I guess you'll have to wait until next year."

"Will you help me look for him?" Felix asked, snuggling closer again.

"Of course, Fe," she promised. "Next year. And if we don't find him, we'll keep looking the year after that. And the year after that."

Felix nodded drowsily. "Thanks, sis."

That night, he dreamed about Sarah's twin. But there wasn't just one. There was a whole group of Sarahs, all looking and sounding a little bit different. And even though he didn't like them all as much as the real Sarah, he woke up grinning, because it had been great to have so many brilliant sisters.

"Oi, Felix. Time to get up, Chicken. Just because your sister's got herself an unscheduled holiday doesn't mean you can lazy about all day too."

Felix gasped and jumped out of bed, into his foster mother's arms. "Mrs S! You're back!"

"Of course I am, love," she said, kissing the top of his head. "Couldn't stay away from you two for long, could I?"

"I'm happy to see you," Felix said, hugging her. And as he followed her to the kitchen, where breakfast was waiting, he'd forgotten all about the shadow twins.