“Fred. Don’t be stupid! You must have climbed up there …”

      “I didn’t climb. I jumped!”

      “What do you mean you jumped? In one go?”

      “Yes.”

      “Without falling off?”

      “Yes.”

      Ellie stared at him. The window was about a metre off the ground.

      “Are you sure?”

      “Ellie. I was just standing there. Next to you. You were looking at the screen. And fiddling with the Controller. Next thing I knew I’d jumped up here.”

      Ellie stared at him some more. Then she noticed something: the blue light on the Controller in her hands, and the blue light on the bracelet around her brother’s wrist, were pulsing in time with each other. Perfectly in time with each other.

      So she said, “Say that again.”

      “Next thing I knew I had ju—”

      “No – before that.”

      Fred frowned. “You were looking at the screen …?”

      “No, in between that and the jumping bit …”

      Fred frowned again. “You were … fiddling with the Controller …?”

      Ellie nodded slowly. “I was, wasn’t I …” she said and not like it was a question. She nodded again. “Fred? Can you just … prepare yourself? I’d like to try something.”

      “Prepare myself? In what way …?”

      “I dunno. Just … make ready.”

      Fred had no idea what that meant. But he took a deep breath and said: “OK.”

      Ellie was the more confident twin. She’d always been the one to make decisions, the one who knew what was what. She was more grown-up, more likely to understand stuff that Fred didn’t, quite, yet.

      But although she was acting like she knew what was what here – taking control, telling Fred to make ready, all that – she didn’t really understand what was going on. She didn’t really think that Fred had got up on to the window ledge in the way her brain was telling her he must have. And she didn’t really think anything was going to happen when she pointed the Controller back at Fred and flicked the control stick downwards, while pressing the emerald button.

      But it did.

      Fred’s legs extended, and he jumped gracefully off the window and landed back on the floor of the playroom.

      “Oh. My. God,” said Ellie.

      “You see!” said Fred. “That’s what happened before! Only in reverse. And … wwwwooaargggh!!!”

      Ellie, who had been smiling in amazement while Fred was speaking, had moved the control stick of the Controller in a circle.

      Which had led to – or, if not, it was a really remarkable coincidence – Fred spinning round in a circle.

      Then, gaining in confidence, Ellie pressed the ruby button and flicked the control stick up at the same time. Leading to Fred – while saying “AAARRGGGHHHH!!!!!” – jumping up in the air and doing a perfect somersault back down again.

      Once he realised he was fine and hadn’t broken anything, Fred, breathless and wide-eyed, said: “Ellie! What’s happening?”

      “You see that bracelet you’re wearing?”

      “Yes.”

      “I think it’s paired with the Controller. I think it pairs … you with the Controller.”

      Now it was Fred’s turn to stare. Then he laughed. “Good one, Ellie! Very funny! Now can we talk about why I’ve started leaping up into the air for no reas— WWWWOOOAAARGGH!” he said as Ellie moved the control stick upwards while pressing the gold button – making him jump up and land with a forward roll on the spare bed.

      “Oh! It’s musty!” he said, coming up near the pillow.

      “Fred, it’s really happening! You’re paired with the Controller! You are my avatar!”

      Fred nodded, finally taking this in. “Are you going to change all my clothes and hairstyle?”

      “No,” said Ellie. “I’m not brilliant at making my avatars look good anyway. That’s your speciality.”

      “Will it work the other way round?”

      “I don’t know …” she said. “Shall we have a go?”

      Fred nodded excitedly. He was about to take the bracelet off – and Ellie was about to hand over the Controller – when, from outside, they heard:

      “HEEEEEELLLLLLLP!!!!”

      The twins ran outside. Standing on the street,

      looking up, was Eric, holding a bacon sandwich, and Janine, not holding Margaret Scratcher. Which meant something was wrong.

      “What’s happened?” said Ellie.

      “MARGARET! MY LITTLE MARGARET!! MY BEAUTIFUL MRS SCRATCHER!!!” Janine was screaming, in between sobs.

      “What about her?” said Fred.

      “She’s up there,” said Eric, pointing, in between munches.

      The Stones, as we know, lived in a ground-floor flat. But next door to their building was a house lived in by the Whites. The Whites were perfectly fine neighbours, except at Christmas. At Christmas, the Whites transformed their house into the biggest Christmas building in the street – maybe in the whole town. Derek White, the dad, strung light bulbs all over the front; above the living-room window was a big neon Santa, laughing in a sleigh with all twelve reindeer a-flying; and in the garden stood an enormous Christmas tree, festooned with every colour of fairy light in the fairy-light spectrum.

      Fred and Ellie liked it actually. But Eric didn’t. Eric thought that Derek was hogging the limelight. To say nothing of how much he was hogging the street’s electricity. And the thing Eric really didn’t like was that Derek built all this and switched it on … at the end of October.

      That really annoyed Eric at the best of times. “Christmas isn’t for ages!” he would always grumble, looking at next-door’s lights from behind the lounge curtains.

      “Oh, Eric. You’re only annoyed because you won’t be getting the turkey and the stuffing and all the trimmings for months …” Janine would always reply.