School No 17 was strange from the entrance. The old part of the building, the one with the cracked staircase and grey-green walls, was said to have been built a hundred years ago. Lena once saw the shadow under the classical clock hesitate, as if time hung in the air for a moment.... But she didn't even tell that to her closest friends Igor and Tim. Today, however, she decided that she would no longer remain silent. - 'Listen,' she said quietly during the break, as they sat on an old bench next to the maths room. - It occurs to me that there is something in this school. Something we can't see because we are looking too shallowly. Igor smiled slightly, but Tim leaned forward, clearly intrigued. - 'What do you mean? - He asked. Lena pulled a small hardcover notebook out of her backpack. She opened it to a page full of smudged drawings and short notes: "a door that isn't there", "a shadow that doesn't return", "rustling in an empty hall". - I've collected some things I've noticed,' she said in a whisper. - I want you to help me check something. After lessons, getting through to the old floor was not straightforward. The corridor was plunged into semi-darkness and the fluorescent light flicked nervously. Lena felt goosebumps on her arms as they approached the door, which she claimed to have seen once and then disappeared. Against the wall, next to a cupboard, where there was usually only a smooth grey surface, Lena pushed the dust away with her hand. She felt a chill, unnatural for a spring day. And then... the shadow of her hand was not reflected on the wall. It simply disappeared. Everyone froze. Igor took a step back, Tim put his hand on the wall right next to Lena. His shadow had also disappeared. - It's impossible... - he whispered. Suddenly the wall began to pulsate gently, cracks appearing on it forming the shape of a door. A strange sound came from within, as if a voice of rustling shadows was whispering their names. All three looked at each other, with hesitation and excitement. The door slowly began to open....