It was an autumn afternoon, and in the garden the wind was playing with the fallen leaves. Skye, Ziggy, Lily, and Dash were all bent down on the ground, busy gathering the prettiest leaves: yellow like lemons, red like strawberries, brown like warm bread.

"Look at mine!" said Ziggy, lifting up a leaf as big as his hand. "It looks like a star!"

"And mine looks like a heart," whispered Lily, holding it gently between her fingers.

Skye smiled in silence. She loved listening more than talking, and right then she liked the soft sound of leaves brushing against the grass. Dash, instead, was running back and forth, throwing handfuls of leaves into the air as if it were raining gold.

Suddenly a sweet whistle came from far away. It was a sound the children knew well.

"CHOO CHOOOOO! CHOO CHOOOOO!"

Everyone looked up. Among the leaves blown by the wind, a soft mist formed, light and smelling of bread and chocolate. It was a different kind of mist: thin, mysterious, that made everything seem wrapped in a gentle hug. And from the mist came Toby the Magic Train, with his kind eyes and a chimney that whistled.

Toby stopped in front of the children and spoke:

"Choo choo, my puffs of mist appear,
a magic day for you is here.
A tower waits up in the sky,
with sleepy lights that long to fly."

The children looked at each other with big eyes. A tower? Lights that don't shine? Without thinking twice, they climbed onto the train, and Toby left in puffs of sweet-smelling steam.

The trip was as short as the flap of a wing. The mist grew thicker, but it wasn't scary: it was a tender mist, like cotton candy. When the train stopped, before them appeared a tall white castle, made of pale stone, with a narrow tower that climbed toward the sky like a finger.

"The Castle of Whispering Mist," Skye read softly, pointing to old writing above the doorway.

"And that must be the Memory Tower!" said Ziggy, his nose pointing up.

The castle door was half open. The four children tiptoed inside and found a spiral staircase that turned and turned, climbing up like a giant seashell. They began to climb.

One step, two steps, ten steps. The stairs made a small "tap tap" under their little shoes.

"How many steps will there be?" Dash asked, laughing.

"So many," Lily answered, "but let's keep going."

They climbed more. The little tower windows were round, and from each one came a beam of misty light that landed on the children's hair like a soft caress.

Halfway up the tower, they found something strange: on a wooden branch hanging on the wall, there was an owl. She had big golden eyes, and feathers the color of the moon. She was so still she looked like a statue.

"Good morning!" said Ziggy loudly.

The owl did not answer.

"Owl, can you hear us?" Dash tried.

Nothing. The owl tilted her head to the side, as if waiting for something.

Skye understood. She came closer, and then closer still, until she was very close to the owl's head. Then the owl opened her beak and said, with a voice as light as a falling feather:

"My name is Whisper Owl. I only speak to those who come close. My words are for attentive ears."

Skye nodded, her eyes shining.

"Up there in the attic," Whisper Owl continued into Skye's ear, "the memories have gotten mixed up. Without order, they fade."

Skye returned to her friends and told them what she had heard. They all decided to climb again. Just a few steps remained, and there was the attic.

When they entered, they were left speechless.

The attic was a round room, with a star-shaped ceiling. And it was flying. Flying with lights. They were fireflies, but not the yellow ones you see in summer: these were colorful, tiny spheres of light in a thousand colors. Pink, blue, green, golden, purple. Some glowed brightly, others were just barely lit, and others still seemed asleep, the color of ash.

"They are the memory-fireflies," whispered Lily, as if speaking too loudly might break something.

"But why are some of them not glowing?" asked Dash.

That's when they saw the wall. The big wall at the back of the attic. There was a riddle drawn on the stone: four simple drawings, in a row. A sun. A wave. A star. A heart. Below, an old writing: "To light them again, give your light to another light."

"What's a riddle?" asked Dash, scratching his head.

"It's a puzzle," Skye explained. "Something to figure out."

The children looked at each other. What did the writing mean?

Skye held out her hand and a pink memory-firefly flew down and landed on her palm. The firefly was warm, but it didn't shine very much. Skye stared at it: inside, she saw an image, one of her memories. It was the morning she had baked a cake with Mom Lisa, when she had spilled flour everywhere and they had laughed until they cried.

"It's my memory," said Skye. "But it doesn't shine."

Ziggy came closer.

"Tell me about it," he said.

Skye began to speak. She told about the flour on Mom's nose, the chocolate on her face, the cake that came out crooked but was the yummiest ever. As she spoke, something magical happened: the firefly on Skye's palm grew warm, lit up, and started to shine a bright, lively pink. A soft, warm light, that lit up Skye's whole hand.

"It glowed!" they all shouted together.

Then they understood. They understood the wall. They understood Whisper Owl. They understood the riddle.

Lily looked around and a blue firefly landed on her shoulder. She turned to Dash.

"Dash, do you want to hear mine?"

Dash came closer.

Lily told about her dad Luke, who had taught her to make soap bubbles, and how they had made one so huge, as big as her head, before it popped and made everyone laugh. The blue firefly began to tremble with light, and then turned blue like the sky after the rain.

It was Ziggy's turn. A golden firefly landed on his finger.

"Listen to me," he said, turning to Lily.

Ziggy told about Sophie, his little black kitten, who one night had fallen asleep on his pillow and had purred so loudly that he woke up smiling, even though it was still dark outside. The golden firefly swelled with light, bright as the sun.

And finally Dash. A green firefly landed on his knee. He turned to Skye.

"Skye, do you want to hear?"

Skye came closer, her eyes attentive.

Dash told about the day he had learned to ride a bike without training wheels. His dad Fred had held the seat and told him to be careful, and then at one point he had let go, and Dash was flying alone down the path of the park. The green firefly turned green like spring grass, and shone bright.

Four lights lit. Four memories told. Four friends.

But then something wonderful happened. The other fireflies, seeing the four lit lights, began to move. They came close to one another, they touched, they whispered secrets. And every time two fireflies met, and one told the other something, both lit up. As if the memories, seeing the friends, had learned to do the same.

In just a few moments the whole attic became a galaxy. A thousand vivid colors. Pink, blue, gold, green, purple, orange, turquoise. A storm of soft, silent light, floating around the children like snow made of stars.

Skye heard a rustle behind her. It was Whisper Owl, who had flown all the way up there. The owl landed on her shoulder, and Skye felt the warmth of the feathers against her neck.

"Come closer," said the owl.

Skye leaned her ear in.

Whisper Owl whispered to her, light as a breath: "Memories are like smiles: they only bloom when you give them away."

Skye repeated it to her friends, word for word. And each one repeated it again, because beautiful words, like fireflies, shine more when they are spoken.

On the wall, the riddle changed: the sun, the wave, the star, and the heart all lit up together, forming one warm light.

It was time to go home. The children walked down the spiral staircase with heads full of light, hands that still remembered the warmth of the fireflies, hearts as light as a feather. In front of the castle, Toby was waiting, puffing steam.

They climbed onto the train. Toby whistled softly and spoke:

"We're heading home with hearts so light,
a memory shared is pure delight.
Who shares the joy will see it grow,
who keeps it close just lets it go."

The little train left through the mist, and the children held hands.

When they arrived home, it was evening. Skye ran to her dad Andy, who scooped her up in his arms. She told him about the tower, the attic, the fireflies. As she spoke, her eyes slowly closed. And as she fell asleep, her dad whispered a thank you in her ear. She smiled in her sleep: now she knew, beautiful things told become light.

And in the garden, where the leaves kept dancing in the wind, a small pink firefly lit up, and then another, and another.