Behind the village, just beyond his grandmother's old cottage, stretched a thick, humming forest. Kacper was seven years old and loved adventures. Berry was a year younger, but always bravely accompanied her brother. One summer morning, they decided to go into the forest to find the legendary blue fern flower. Grandma told them that whoever found it would be lucky for a whole year! The forest was full of birdsong and the smells of herbs. The sun was breaking through the leaves, creating colourful patches on the ground. Kacper led the way, with Berry clinging to his rucksack. Soon they reached a big old oak tree. Under the tree sat a small, bearded gnome wearing a green hat. He waved a paw at them. "Hello, children! What are you looking for?" asked the gnome, with a twinkle in his eye. They told about a blue flower. The gnome scratched his chin and said: "Hmm, it's not that simple. There is a mermaid in the forest who knows where the flower grows. But to meet her, you have to find her favourite song!" Kacper and Berry looked at each other. How were they supposed to know what song it was? But after only a moment, they heard quiet laughter coming from behind the bushes. They moved in that direction and the leaves started rustling louder and louder. The brother and sister carefully pushed back the twigs and suddenly saw something bright flashing between the ferns. What was it? Was it the ruscus itself? Or was someone else waiting for them on the other side?