Kacper sat on the windowsill of his room and stared at the sky. It was after the storm. The sun was breaking through the scattered clouds, making the air smell fresh, and a rainbow stretched like a ribbon appeared on the horizon. The boy sighed and looked once again at his sketchbook, in which he had drawn a flying bicycle. - It's a pity such things don't exist,' he muttered to himself. Suddenly he heard a quiet clatter outside the window. He opened it and saw that on the ledge was sitting... a blue sparrow with a small letter attached to its paw. - Hello! - called out someone from downstairs. It was Lila, his neighbour and best friend. - You have to see this! They ran down the stairs together into the garden. There, behind the currant bushes, they discovered a plan rolled up - it was a map written in coloured crayons. It showed the way through the garden, into the attic and... straight to the top of the rainbow. Their hearts beat faster as they climbed the old staircase. The higher they climbed, the more all around them smelled of candyfloss and raspberries. There was something flickering in the attic. There stood a handsome bicycle... but not an ordinary one. Instead of wheels, it had slowly rotating clouds, and the handlebars were entwined with silvery threads. - Shall we try it? - Lila asked. Her eyes sparkled with excitement. Barely had they got on, the bike lifted slightly, softly and quietly, like a feather. They flew through the window, up above the rooftops of the town, until they touched the rainbow. A moment later they found themselves in a completely different world. Below them stretched a vast land on a cloud - a town with houses made of foam, swings on ropes made of mist and slides that led straight into fluffy pools. There were unusual creatures walking the streets - a dog in a hat, a pink dragon with an umbrella and giraffes with twisted balloons around their necks. Suddenly, someone stopped their cloud bike. A tall, stick-thin boy in a tailcoat with silver buttons emerged from around the corner. - You have arrived just in time. We need your help... Kacper and Lila looked at each other with wide eyes. What were they supposed to do in the sky city? Who was this clouded figure and why had all the inhabitants stopped laughing, glancing every now and then towards the mysteriously shimmering tower at the end of the rainbow bridge? After a while, they decided to set off towards the tower, and as they crossed the cotton wool gate, they heard a quiet whisper: - Be brave!.... And then everything around them began to change....