Basia, Kuba and Igor were sitting on the steps leading to the school basement. Actually, they weren't supposed to be there, but who would worry about prohibitions when curiosity was winning over reason? The older part of their high school's building held many secrets, and ever since Mrs. Wozna had talked about strange voices coming from underground, the three of them couldn't think of anything else. Basia was the first to find the tiny metal door hidden behind the brush cupboard. The door was rusty, but there was an engraved, cracked clock on its surface. Cuba pushed the door with his shoulder. It creaked and opened inwards. To their eyes appeared a narrow staircase leading downwards, where there was a cool, damp smell of dust and old moss. With each step, the torchlight brought out more parts of the underground corridor from the darkness. At its end stood a huge, old-fashioned clock with a pendulum whose dial was cracked and whose hands were arranged in a strange letter 'V'. Igor pressed one of the rusty cog wheels. They heard a quiet hum, and the clock flashed with a bright blue light. Suddenly the floor trembled, the walls began to move, and images appeared before their eyes: knights on horseback, strange machines, unknown cities. The world whirled around them, until finally they felt themselves falling.... and everything went out. When they opened their eyes, they saw that they were standing in the middle of a cobbled square, surrounded by people dressed in ancient medieval costumes. The clock was ticking quietly before their eyes, and the hands moved of their own accord. Basia looked fearfully at the boys: - What are we going to do now? At the same moment a man in a coat approached them and whispered: - We have been waiting for you. You have only one chance to get back... - then he pointed at the clock, which had just started to fall to pieces....