Fog floated low over the cobbled courtyard of the Shadow Academy, and the silvery moonlight turned the tall towers into black, jagged silhouettes. Lena leaned against the cold stone of the wall, listening to the muffled footsteps of her friend. Victor slipped out of the shadows, clutching something shiny in his hand. - 'I found this next to the old well,' he whispered and unrolled a piece of velvet cloth. On it lay a metal key with an engraved hourglass symbol. There was a sense of tension in the air - strange things had been happening at the Academy for weeks. The shadows in the windows moved on their own, and the clock on the tower only struck the full hours when no one was looking at it. Lena, from her first day of school, had felt that the Academy's underground hid something more than just dust and cobwebs. - 'This is the key,' she said quietly. - It must open the door under the astronomy room. Have you heard of the Clock of Darkness? Victor nodded. Rumours of an ancient artefact that can stop time had been circulating among the students for years, but no one had dared to check what was hidden on the other side of the locked door. Lena reached out for the key, feeling its weight and coldness. Together, by torchlight, they walked down the spiral staircase until they stopped in front of a small iron door. The lock showed the grooved shape of an hourglass. Lena took a deep breath, inserted the key and turned it. The door opened with a groan. Behind them stretched a narrow corridor in which time seemed dense and still. From afar came a quiet ticking, the echo of an invisible mechanism. Suddenly, a pale light flashed. At the end of the corridor appeared a figure in a black cloak, whose hood hid his face. Lena and Victor froze in place, and the silent ticking of the clock suddenly accelerated, as if someone had just started an ancient mechanism....