It all started during an evening walk when Lena, instead of going straight home, turned down a side street. She was almost of age and had lived in the town forever, but none of the maps showed this path. There was silence all around, broken only by the rustle of leaves and the distant sound of a tram, although trams hadn't run here for years. At the end of the alley stretched a wall, behind which were the ruins of an old factory. Lena noticed something strange on the roof: there was a tree growing there, a huge, spreading tree, as if it were growing straight out of the bricks. The green of the leaves pulsed with an unsettling light, sometimes flickering with colours that Lena knew neither from nature nor from dreams. She climbed the decrepit stairs to the roof, drawn by the flickering glow. Each step seemed more unreal than the last. The chill on the roof was different from that of the evening. The shadows of the factory chimneys seemed to move, as if rippling to the rhythm of an invisible melody. Lena touched the bark of the tree; under her fingers she felt a pulsing, a warmth, as if streams of light were flowing under the bark. Then she heard a whisper that was not quite a voice, but rather a thought that did not belong to her: "You can see us, for the time has come." A boy, about her age - with eyes reflecting that mysterious light - emerged from behind a tree. For a moment they were silent. Behind Lena's back, the city stretched out like a model, but no light in the windows seemed real. "Not everyone ends up here," he said quietly. "There are worlds that only appear after dark and only for those who are not afraid to see. Do you want to know what's next?" Lena looked once more at the tree, at the boy, at the pulsing city below them. She knew she had to make a decision. Then more whispers echoed from deep in the tree - something that sounded like a call, or a warning....