Ziggy was building the biggest castle in the whole world. He had put three sofa cushions on top of each other, then he laid a red blanket over them, and now he was trying to stick a wooden spoon on top, like a flag.

"My castle is the tallest!" said Ziggy, hopping on one foot with happiness.

"No it's not, mine is prettier!" answered Lily, who had built her castle with the armchair cushions and put a row of stuffed animals in front like guards. Her blue eyes sparkled with determination.

Skye, sitting on the floor with her legs crossed, was putting a soft little blanket over her castle, which was small but made with so much care. "My castle is for sleeping" she said in her quiet little voice, and she yawned just a tiny bit.

"Mine is the fastest!" shouted Dash, who hadn't built a castle at all but a sort of car made of cushions, and he was sitting inside it making engine noises with his mouth.

Ziggy laughed. "Dash, castles don't go fast!"

"Mine does!" said Dash, and he pretended to steer.

Sofia, Ziggy's black kitty, was curled up on one of the castle cushions, purring away. Dora, the tabby cat, walked back and forth like she was checking that everything was in order. Poldo, big and chubby, was sleeping on the armchair, and Milo, the most nimble one, had jumped to the top of the wardrobe and was watching everyone from up high.

Outside the window, the sky was full of white clouds. One looked like a bunny with long ears. Another one looked like an elephant spraying water from its trunk. Ziggy watched them for a moment, then went back to playing.

It was right at that moment that they heard the sound.

CHOO CHOO!

Ziggy dropped the wooden spoon. Lily jumped to her feet. Skye opened her eyes wide. Dash stopped making engine noises.

"Toby!" they all shouted together.

They ran to the window and there, in the garden, was Toby the Magic Train, with his white steam rising into the evening sky. Toby whistled, then said in his happy voice:

"Climb aboard, my dear friends, climb on tight,
we're off to a mountain that sparkles with light!
Where snow shines like silver upon every tree
and stars come to rest where the whole world is free!"

The four children put on their shoes in a hurry, their coats, and climbed onto the little train. Toby left with a big CHOO CHOO and started to climb. He went up, higher and higher. The houses became tiny like toys, then the clouds passed around them like soft fog, and then the clouds were below them.

Toby kept climbing. The air became cold, and the children huddled in their coats. Then, all of a sudden, Toby stopped.

In front of them was a huge mountain, all covered in white snow that looked like powdered sugar, that sweet dust you put on cakes. And in the sky, above the mountain, colorful lights were dancing, green and purple, moving like silk ribbons. They're called auroras, and they are lights that the sky turns on during special nights, like a party of colors.

"How beautiful!" whispered Skye, with her eyes wide open.

"It looks like a giant cake!" said Dash, and he felt a little hungry just looking at it.

They climbed down from the train and put their feet in the snow. It was soft and crunchy under their shoes. Ziggy started walking right away, because he was curious to explore. Lily followed him, determined. Skye walked calmly, and Dash ran a bit ahead and a bit back, like he always did.

"Look!" said Ziggy, stopping suddenly. "What are those?"

In the snow there were footprints that glowed. They weren't shoe prints, or paw prints. They were small, round, and they sparkled with golden light, as if someone had walked leaving little pieces of sunshine on the ground.

"Let's follow them!" said Lily, who wasn't afraid of anything.

The glowing footprints led them behind a big rock covered in ice. And there, huddled in the snow, they found something extraordinary.

It was a little star. Not a drawn star, but a real little star, small as an apple, that glowed with a golden light that came and went, like the beating of a heart. And she was shaking. She was shaking from the cold, and her light was weak.

"Oh!" said Skye, putting her hands over her mouth.

Ziggy came closer and crouched down. He smelled a sweet scent, like warm honey. "Hello" he said in a gentle voice. "What's your name?"

The little star looked at him with her shiny little eyes. "My name is Twinkle" she said in a thin little voice that trembled. "I came down from the sky because I wanted to know something."

"What?" asked Dash, coming closer.

"I wanted to know what a hug is." Twinkle did a little bounce on the snow, and where she touched, a golden footprint stayed behind. "Up there in the sky, we stars shine close together, but we never touch each other. I heard the children on Earth talk about this thing, a hug, and I wanted to understand what it is. But now I'm so cold and my light is going out."

Ziggy felt something strong in his chest, like when he saw a little kitten soaking wet in the rain. "I promise I'll warm you up!" he said, and he sat down next to Twinkle to give her some warmth with his body.

"What a cute little star you are!" said Dash with a big smile.

And right at that moment something very funny happened: Twinkle sneezed! But it wasn't a normal sneeze. From her sneeze came a little cloud of golden glitter that flew through the air and came down like sparkly snow.

"ACHOO!"

The children stood with their mouths open, then burst out laughing. Twinkle turned all red, well, her light turned a little pinkish. "It always happens when someone is nice to me" she said, feeling shy. "I can't help it."

Ziggy laughed, but then he became serious. Twinkle was still shaking, and her light kept getting weaker.

"Why don't you go back up to the sky, where it's not so cold?" asked Lily, practical as always.

Twinkle lowered her little eyes. "I made a promise to the Moon. I promised her I would come back with the answer to the question: what is a hug? But if my light goes out before I understand, I won't be able to fly back up and the Moon will be without an answer forever." Twinkle held in her little arms of light a small glass bottle, clear as a raindrop. Inside was a tiny droplet that glowed with white light. "This is the last drop of the Moon's dew. She gave it to me, and I promised to keep it safe always."

Ziggy nodded. He knew that promises are important. When you promise something, you have to keep it.

But then Lily pulled Ziggy's sleeve. "Ziggy, come look."

The children walked a little further ahead and found something sad. A stream coming down the mountain was completely frozen, still like a glass statue. And around the stream there were animals who were thirsty. A family of hedgehogs — do you know what hedgehogs are? They're small little animals with lots of soft spines on their backs, and when they're scared they roll up like a ball — was standing near the ice, and the baby hedgehogs were all curled up from the cold. A baby chamois — a chamois is a kind of mountain goat, with small horns and strong legs — was standing nearby, teeth chattering.

"They're thirsty but the water is frozen" said Skye, with a sad voice.

"And they're cold" added Dash, who had crouched down near the baby hedgehogs.

The wind blew harder. Snow fell from the tree branches. The aurora in the sky flickered like a candle. Ziggy turned around and looked at Twinkle: her light was now very, very faint, like a little night light almost out of battery. The baby hedgehogs were trembling. The baby chamois had lain down on the ground.

Ziggy felt fear rising in his belly. It was so cold. Twinkle was fading. The animals were suffering. And he had made a promise.

"What do we do now?" said Dash, and for the first time his voice wasn't funny, it was worried.

Lily clenched her fists. "We have to do something!"

Ziggy closed his eyes. He thought about his promise. He thought about Twinkle who wanted to know what a hug is. He thought about the warmth he felt when Mom Kate held him tight. He thought about when Dad Mike held him on his lap and he could feel Dad's heart beating next to his own.

And then he understood.

"I have an idea!" said Ziggy, and his eyes sparkled. "Everyone here, close to me! Let's hold each other tight!"

"What?" said Dash.

"Trust me! Come here, everyone, close to Twinkle!"

Lily was the first to move. She stood next to Ziggy and took his hand, tight tight, the way she always did, with all her strength. Skye came close on the other side and rested her head on Ziggy's shoulder, soft and calm. Dash ran over and squeezed in the middle, and hugged everyone with his quick little arms.

"Now Twinkle, come here, right in the middle of us" said Ziggy.

Twinkle, with her light now just a tiny little dot, bounced into the center of the circle of children. She was so small she fit in the palm of a hand.

The four children held each other tight. Ziggy could feel Lily's heart beating near his arm. He could feel Skye's calm breathing. He could feel the warmth of Dash who never stayed still. And in the middle of them, Twinkle.

A moment passed. Then another.

And then something magical happened.

The warmth of the four children holding each other tight began to grow. It wasn't just the warmth of their bodies. It was something bigger. It was the warmth of when you love someone and you tell them without speaking, just by holding them tight.

Twinkle felt that warmth reach deep inside her light. And her light began to come back. First a little, then more, then even more. It became warm, golden, bright like a little sun.

The snow around the children began to melt. The drops of water ran down toward the frozen stream. And the stream, with a sound like a sigh, began to flow again, first a tiny drop, then a thin thread of water, then a whole little river.

The baby hedgehogs lifted their little noses and ran to drink. The baby chamois got up on its legs and drank for a long time, with its nose in the fresh water.

Twinkle, in the middle of that hug, closed her little eyes. And she smiled. "So this is what it is" she whispered. "A hug is when you feel someone's heart close to yours. It's when you're not cold anymore, even if it's snowing outside. It's when your light comes back, because someone is holding you tight."

"ACHOO!" She sneezed the biggest cloud of glitter of all, and the children laughed so hard that their laughter echoed across the whole mountain.

Twinkle's light was now so strong, golden and warm. She shone so bright that the aurora in the sky seemed to bow to her.

Twinkle looked up. "Now I can go back to the Moon. I have the answer to her question. And I kept my promise."

"And I kept mine" said Ziggy, smiling.

Twinkle did one last bounce on the snow, leaving the brightest footprint of all. "Thank you, Ziggy. Thank you Lily, Skye, Dash. Now I know the most beautiful thing on Earth."

Then she flew up, light as a soap bubble, and rose into the sky. She rose and she shone, she shone and she rose. And when she got all the way up there, in the sky full of stars, she became the brightest star of all. The Moon smiled at her, and Twinkle whispered the answer.

The children stayed watching her, with their noses pointing up.

"I can see her!" said Dash. "She's the one that shines the most!"

"She'll shine forever" said Skye, and she yawned just a little.

Lily didn't say anything, but she smiled. And her blue eyes were shining too.

Ziggy felt his heart full of something big and warm. He knew that every night, from his bedroom window, he would look at the sky. And he would find Twinkle there, the brightest star, the one that smells like honey and sneezes glitter. The one who now knew what a hug is.

CHOO CHOO!

Toby the Magic Train whistled. It was time to go home. The children climbed on, tired and happy, with red cheeks and warm hearts. Toby puffed a cloud of steam and said:

"A hug given truly from deep in the heart
can melt all the snow and the cold falls apart.
Who keeps every promise they've made to a friend
has a treasure much greater than gold in the end!"

The little train went down the mountain, through the clouds, over the lit-up houses, and stopped in the garden. The children climbed off and waved goodbye to Toby.

That evening, when Dad Mike tucked Ziggy into bed, Ziggy said: "Daddy, do you know what a hug is?"

Dad Mike smiled. "What is it?"

"It's when you feel someone's heart close to yours."

Dad Mike held him tight, and Ziggy felt Daddy's heart beating next to his own. Then he looked out the window. And he saw her. The brightest star in the sky, shining with golden light.

"Goodnight, Twinkle" whispered Ziggy.

And the star, up there, shone just a little bit brighter.