A new day was beginning at the Oak Tree School. Class one b was almost ready for their lesson. Mrs Ela, their teacher, smiled at the children and showed them to the big black board. "Today each of you will draw your dream friend with chalk!" Zosia took a pink chalk out of the box, Franek chose a green one and Benio decided to use a blue one. One by one the children came up and drew colourful characters, hearts, flowers and balloons. It was very fun. Suddenly, when Kuba wanted to draw a rocket, he noticed a bright, glowing mark on the blackboard. It didn't look like a normal line. It was twisted, as if the chalk had danced on its own. Kuba called out to his friends: "Look! Something left this mark here!" All the pupils looked at the blackboard. Indeed, there was a thin, colourful footprint stretching across the classroom and disappearing under one of the desks. The children came closer. Zosia, the bravest of the class, opened her eyes wide and said in a whisper: "And maybe this leads to something special?" Mrs Ela looked on curiously. "We can see where this trail ends. But we have to be very careful and work together!" The children squeezed into a group. Frank crouched down by the bench and moved slowly, watching the trail that led farther and farther away, until he reached a door at the end of the corridor. They all quietly followed him, their hearts beating faster with each step. Behind the door waited something they had never seen before. They didn't know what they would find, but they were already very close. They stopped right in front of the door, from behind which came a quiet, rhythmic tapping....