That morning the sky was a soft grey, like a cozy blanket pulled up over the houses. It was cold, the kind of cold that nips your cheeks and makes you giggle for no reason. Lily, Ziggy, Skye and Dash were in the garden, all bundled up in scarves and hats, building a slightly crooked snowman.

"The carrot goes here, for the nose!" said Ziggy, hopping up and down.

"No, higher up!" laughed Dash, who had already slipped twice on the ice, tumbling over in funny somersaults.

Skye, calm as always, was setting two little pebbles for the eyes. Lily, with her blue eyes and her bold look, pressed the snow hard to make the belly nice and round.

That was when they heard it. From far away came a sound they knew very well.

"CHOOO CHOOO!"

Through the snowflakes drifting down slowly came Toby the Magic Train, all colorful, with white smoke that mixed into the snow. He stopped right in front of the gate, blew his little whistle, and said:

"Hop on, dear friends, while the snow falls so light,
I'll take you to seas that go singing all night!
A light far away has forgotten to shine,
and an old, dear friend is waiting — he's mine!"

The four children looked at each other, their eyes sparkling. They left the snowman half done and ran to climb aboard. The doors closed with a gentle puff and Toby set off, gliding across the white fields.

The journey was wonderful. They sped past hills covered in snow, then the ground began to rise, and rise, up to a very tall cliff looking out over the sea. And there, on top of the cliff, stood a lighthouse.

"That is a lighthouse," Lily explained to the others. "It's a tall tower that lights up a big light at night to tell the boats where to go, so they don't get lost in the dark."

The lighthouse was called Lampo, and he was old and friendly. The snow settled on his roof like powdered sugar. But there was something strange: his light, up at the top, was pale and trembling, like a tired little candle.

Toby stopped at the foot of the tower. The children climbed down and went up the many spiral steps, all the way to the top. And there, inside a big round room with windows all around, they found a turtle.

She was huge and ancient, her shell covered in drawings like a map of all the seas in the world. She was smiling, and the moment she saw them she burst out laughing.

"Ha, ha! Welcome, little sailors! I am Coralla, the traveling turtle! I have sailed every sea there is! Ha, ha!"

"Wow!" said Dash. "Tell us a story!"

Coralla told of waves as big as mountains and of fish that sang, and with every sentence she laughed, and laughed, and laughed. But Lily, who was paying attention, noticed something. When Coralla laughed too loudly, her eyes stayed a little sad.

Ziggy leaned out of a window and looked down at the sea. "Hey… but the sea is all grey!"

Everyone ran to look. It was true. Below the lighthouse, the water was not light blue, not green, not deep blue. It was grey like ashes, dull, without a single color.

"That's why Lampo's light is sad," whispered Skye. "He has turned grey inside too."

"Oh, that?" said Coralla, laughing again. "It's nothing! Silly little thing! A tiny nothing at all! Ha, ha!"

But Lily didn't believe her. She clenched her fists. "Coralla, the sea has lost all its colors. That is not a silly thing. We want to help it."

The turtle stopped laughing for a moment, then started up again, louder than before. "All right, all right! If you really want to… down at the bottom of the sea there is a knot. A great big knot that has trapped the current of colors. But it's far too hard, just give up, ha, ha!"

"We never give up on anything," said Lily, firmly.

Then from below came Toby's voice, for he had blown a little of his magic dust into the air:

"I blow my magic, soft as a feather,
now breathe underwater, we'll swim down together!
Dive deep with me, with your heart true and clear,
and find at the bottom what's hidden and dear!"

The children felt their bodies grow light. They held hands, climbed onto the windowsill, and dived down into the grey sea.

Splash! And it was magic: they could breathe just fine, as if the water were air. But all around them everything was dull and silent. The seaweed was grey, the fish were grey, even the shells seemed made of dust. Not a sound could be heard. It was a sleeping, sad sea.

"How sad," said Skye softly, and she almost wanted to cry.

They went down deeper and deeper, until they saw it: in the middle of the seabed was a giant knot, made of many braided ropes of seaweed. It was as big as a house, and inside, trapped, you could just glimpse a little colored light wriggling to get out.

"That's the current of colors!" Ziggy understood. "It's locked up in there!"

"Let's pull it out!" shouted Dash.

Everyone grabbed the ropes of the knot and pulled with all their might. "One, two, threee!"

But something strange happened. The more they pulled, the tighter the knot got. It grew smaller and harder, as if the struggle made it angry.

Dash tried, quick, circling around to find the loose end. Nothing. Ziggy tried, with a clever idea, using a shell as a lever. Nothing. Skye tried, gentle, stroking the ropes. The knot didn't budge a thread.

"We'll never do it," said Dash, sitting down on the seabed, discouraged.

Ziggy lowered his head too. And so did Skye. It really did seem impossible.

But Lily looked at the knot, and thought. She thought of the grey sea. She thought of Coralla, who always laughed, even when her eyes were sad. And all at once something came to her mind.

"Wait," she said. "Maybe the knot doesn't come undone by pulling. Maybe the knot isn't the real trouble. Maybe… the real problem is higher up."

She swam quickly back up, through the dull water, up the tower, to the round room where Coralla was waiting with her usual smile.

"Well? See, it's impossible? Ha, ha!" said the turtle.

Lily came closer, slowly. She didn't laugh. She looked her straight in the eyes and asked the question no one had ever dared to ask her.

"Coralla… but you, how are you really?"

The turtle opened her mouth to laugh. But this time the laugh didn't come. She went still. Her lip trembled. And for the first time in a very long time, in years and years, Coralla stopped smiling.

"I… I am tired of traveling all alone," she said in the faintest voice. "All the seas I've seen, I've seen them with no one beside me. Inside me there is a big sadness, but I was always afraid to show it. So I laughed, I laughed all the time, to hide it. But the more I hid it… the greyer the sea became. Because the grey sea, little Lily… the grey sea is my heart."

And then it happened. A big, shining tear rolled down Coralla's cheek. Then another. The turtle cried, at last, and as she cried Lily took her paw.

"It's okay to be sad, Coralla," she said softly. "It's okay to cry. All feelings are okay. You don't have to hide them. We are here."

Skye, who had come back up with the others, hugged the turtle. Ziggy and Dash stood close beside her.

And at that very moment, down at the bottom of the sea, the great knot went "CLICK". It loosened. All by itself. As if by magic, the ropes came undone one after another.

The children ran to the window. The little light of colors, free at last, burst into the sea like a thousand fireworks. The blue came back, and the green, and the red of the corals, and the orange of the fish, and the yellow of the starfish. The colors chased one another through the water, happy, in every direction. The sea was alive again, bright, beautiful.

And the light of Lampo the lighthouse, at the top, blazed strong and warm, shining as never before.

Coralla was laughing again. But this time it was a real laugh, one that came from her heart, with a few tears still in her eyes.

"Thank you," she said. "Thank you for listening to me."

The snow, meanwhile, had stopped falling. The sky had opened, and above the lighthouse a great colorful rainbow had appeared, with all the colors of the sea come alive again.

When it was time to go home, Toby the Magic Train was waiting for them at the foot of the cliff, with his "CHOOO CHOOO". The children said goodbye to Coralla with a long hug and climbed aboard.

As the train started off across the fields, Toby said:

"When a sorrow is hidden and tucked out of sight,
it grows ever bigger, more grey, and less bright.
But tell it to a friend who is loyal and true,
and your heart fills with color, with bright sky-blue!"

The children looked out the window at the sea glittering far away, and smiled. They had understood something important: that laughing is okay, but crying is okay too, and that feelings, every single one of them, must never be hidden, but listened to with love.

And so, among the last snowflakes and the rainbow, they went back home, where their snowman was still waiting, a little crooked, but more beautiful than before.