Deep in the humming forest, where the birds sing and the squirrels jump on the branches, lived the curious mouse Pola. Every morning, Pola wandered to the Forest Lake to see what new things the day would bring. One morning, as the sun's rays danced on the water, Pola met her friend Tadek the frog. Tadek was extremely excited. - Pola! Come quickly! - he called out. - There's something shiny lying in the grass by the lake! The mouse and the frog ran towards the mysterious place. There, between the blades of grass, shone a colourful pebble. But the longer they looked at it, the more it seemed to shine with its own light! - Maybe it's a magic stone? - whispered Pola. Tadek stared with wide-open eyes. As Pola reached out her paw to touch it, suddenly something rustled from the reeds.... What was it? Who else was hiding by the lake? Pola and Tadek froze motionless, waiting to see what would happen next....