Lena had always enjoyed exploring the nooks and crannies of her old school. After ten years of teaching, she knew every corridor, every creaky floor and even the hidden exit to the roof. But one cloudy afternoon, when a storm was raging outside, she stayed after lessons to help the teacher in the library. As she removed books from the bottom shelf, an old map of the building caught her eye. At the end of one corridor, in a place where it had never been, was drawn a small door signed: "Door of Mist". Curiosity did not let Lena rest. She decided to look for this place. As soon as class was over, she slipped out of the library and followed the directions on the map. The corridors she followed seemed more and more deserted. Rarely did anyone look in there, and the windows were dull with dust and overgrown with cobwebs. At last she stood before a forlorn, carved door she had never seen before. It was covered in a thin layer of mist, as if it itself leaked from a crevice beneath. Lena hesitated, but curiosity was stronger than fear. She reached out and touched the handle. The door opened silently, allowing her to step inside. On the other side, silence reigned. A thick fog enveloped her, and the space seemed much larger than its location in relation to the school would suggest. Suddenly, shadows emerged from the mist - silhouettes of other children Lena had never seen before. Each had a spark of mystery in their eyes, and luminous butterflies floated around them. One of the children approached Lena and smiled mysteriously. "Welcome to the other side of the school," it said in a whisper. "We knew you'd end up here one day. But are you ready to learn the real secret of the Door of Mist?" Before Lena had time to answer, the mist around her thickened and the butterflies arranged themselves in the shape of an old key. Strange whispers began to echo in the air - and Lena realised that she had just taken the first step into a world she had never even dreamed of....