Penny was building her pebble castle in the garden. The sun warmly stroked the grass blades, and the geranium smiled red in the pot. Suddenly something glittered under the pot.

"Wow!" Penny bent down. A tiny key lay there. Red and blue dots glittered on the key, and a green ribbon fluttered from its end. A cardboard card was tied to the ribbon. On it was a drawing: a tiny leaf.

"Marty, look!" – said Penny.

Marty the Squirrel thudded down from the walnut tree. His bushy tail trembled with excitement. "Investigation! This is an investigation key!" His eyes glittered.

Penny read the cardboard. "Where the wind laughs and the song rings, there rests the first sign."

"Where does the wind laugh?" Marty scratched the base of his ear.

Penny looked around. On the veranda the wind chime tinkled. "There rings the song!" she pointed.

Under the wind chime, a clothespin held another cardboard. On it were three dots: two red and one blue. Beneath it, a small arrow pointed toward the sandbox.

"Let's go!" – whispered Penny. They ran to the sandbox. On top of the sand, they found spotted pebbles arranged in a row: red, red, blue.

"The same as on the cardboard!" – said Marty. Hidden under the third, blue pebble was a flattened, flat stone. On one side of the stone a little leaf was drawn, on the other side was written: "I am like an umbrella, but I don't fear the rain."

"An umbrella that doesn't fear?" – pondered Penny. "That is a tree! The big walnut tree!"

At the bottom of the walnut tree, moss grew like a soft cushion. Among the moss, a thin, dotted ribbon winked at them, with a tiny bell at its end. The ribbon led to where the roots met. There, a tiny wooden box rested. On the box's lock was a leaf-shaped pattern, and around the lock red-blue dots danced.

"Just like the key!" – enthused Marty.

Penny carefully inserted the polka-dot key. Click! The box popped open. Inside, soft silk cushioned an even smaller, shiny metal box. On the side of the metal box was a sunflower crank. Penny slowly turned it.

A tinkling melody crept out, cheerful and jumpy. Under the silk, they found a folded paper too. Penny unfolded it. On the paper, written in big, round letters, was this message:

"Greetings, Clever Detectives! If the music plays, look for the dots where it is good to sit. At the third place a new secret waits."

"The bench!" Marty jumped. At the end of the garden stood the bench, on its backrest, mushrooms painted with dots.

Penny sat down and started to count. "One spotted mushroom, two spotted mushrooms, three..." Under the hat of the third mushroom, a tiny pocket lay hidden. Inside it was a round little mirror. On the back of the mirror, this message was written: "Look into it, and you will see the most important clue!"

Penny peeked into it. In the mirror she saw her own smile, next to it Marty's curious eye.

"Our face is the clue?" – gasped Marty.

Under the mirror, one more row of letters was hidden: "Who asks and notices, always finds what he looks for." Under it a drawing: a pebble path, with a small sun at its end.

"To the pebble path!" – decided Penny. On the garden path, some of the pebbles had painted red or blue dots. Penny, remembering the first sign, followed the pattern: red, red, blue. At every step, the melody of the box tinkled in her pocket, as if in agreement.

At the end of the path, at the flowerbed shaped like a small sun, a glass bottle stood on the ground, containing a paper strip. Penny pulled it out. She read this:

"Dear Penny and Marty! I am the Garden Gnome. I am giving the polka-dot key to you. Open with it the door of curiosity whenever you want. The tinkling box is yours: if you turn it, it will always remind you how good it is to ask, pay attention, and investigate together. P.S.: Under the geranium tomorrow a new sign will grow."

Penny smiled at Marty. "Then tomorrow will be a detective day too."

"And spotted!" – laughed Marty, and the tinkling melody danced around the garden again.