Leon always felt that there was more hidden in his school than the eyes could see. Ever since he came here to high school, he had been fascinated by the old corridors, the glass doors leading to inaccessible storerooms and the library - the oldest part of the building. There, among the bookcases up to the ceiling, he felt as if he was crossing the boundaries of time. It was Friday evening, the sun had long since set, and they - Leon and Zosia - had stayed in the library after hours, supposedly helping Mrs Jola arrange books. In fact, they were both looking for an adventure, although neither of them had thought about how much their lives would change today. Zosia pushed aside a volume of 'Labyrinths of Time' and then a cool breeze came from the darkest corner of the library. Leon, intrigued, walked over to a bookcase with a metal "Special Collections" sign. In the wall, just off the floor, he saw a thin, vertical crack. Had it always been here? After a moment's hesitation, he slid his fingers into it - and suddenly the whole wall swung open like a door. Zosia, with a pounding heart, stood next to him. Beyond the door stretched a dark corridor, with a dark blue glow flickering at the end of it. Leon turned on the torch on his phone. Zosia squeezed his hand. "Shall we go?" she asked in a half-hearted voice. "We don't have a way out," Leon whispered, feeling coming what he had been waiting for all his life. The corridor seemed much longer than the school building would have allowed him to believe. When they finally reached the glow, they found themselves in a huge hall with walls of black glass. In the middle of this hall hung something like a crystal in which colourful streaks of light swirled. In each of the walls was reflected their own reflection - different, older, younger, some strangely familiar, others quite alien. A voice sounded from behind the crystal - quiet, as if whispering through a closed door: "Welcome, explorers. The trial is just beginning. Will you find the exit before time runs out?" Zosia looked terrified at Leon. In that second, the glass floor beneath their feet began to crack....