Cuba has lived at the end of Maple Street forever, but he never imagined that the most extraordinary adventure of his life would begin just beyond his neighbour's old fence. That day, when he and Lena found a strange, yellowed map in a dusty book in the school library, everything changed. On the map was drawn the forest behind their block of flats, and in the middle was a mysterious drawing of a tower with the words: "For the brave only". Cuba looked at Lena and smiled broadly. - Shall we go? - Sure! - she replied with a sparkle in her eye. At dusk, with torches, backpacks and sandwiches, they made their way through an overgrown gate into the forest. Footsteps tread quietly on the soft moss and shadows stretched between the trees. The forest smelled of needles and dampness, and every rustling sound gave them a pleasant shiver. Kuba held the map, Lena looked out for signs. After a quarter of an hour, they found a strange green symbol on a tree: a circle with three dots. - That's definitely it! - whispered Lena. - Come on, look, there's an arrow to the right on the map! They followed it deeper into the mysterious forest until finally, when the lights of the city became just a pale glow behind the trees, they saw it. The Green Tower rose amidst dense bushes, overgrown with ivy and even larger than they had expected. There was a light of some kind flickering at the top. - Can you see it, Lena? I think there's someone up there! Suddenly, just inside the tower door, someone's figure in a strange hat slid out of the darkness. The figure looked at them and nodded for them to come closer. At the same moment they heard a quiet, mysterious whisper: - Only for the brave... Kuba and Lena exchanged surprised glances. Should they go inside? Would what they would find inside the tower be as fascinating as the map and the mysterious sign? Anything could happen now.