The old, overgrown villa on Lipowa Street caught the eye of passers-by almost every day, but no one except Ola, Igor and Majka dared to look inside. To many, it was just another building with a locked door and broken windows. To them - it hid something more. One August afternoon, Ola, the bravest of the three, forced her friends to go on an expedition. "If you're really curious, come along. Maybe we'll find some old treasures there!" - she chuckled, smiling wryly. Igor rolled his eyes, but set off first, and Majka - despite her initial misgivings - followed them. They jumped over a low fence and stood on the creaking porch. The inside of the house smelled of dust and damp, and the echo of their footsteps echoed off the cracked walls. In the room to their left they found overturned armchairs, remnants of china and something strange under the carpet. Igor bent down, moved the carpet. Underneath it was an old wooden clapboard with a faded, hand-painted letter 'M'. Majka swallowed her saliva. "What could that be? Maybe we'd better not move..." But Ola, pushed by curiosity, was already tugging at the flap. Inside, amidst the cobwebs and dust, lay a heavy iron box with a mysterious lock. Next to them, the floor shook, as if something deep beneath the house was trying to move. They heard a deafening, rhythmic sound coming from under the boards. Igor looked at the others, and his voice trembled: "Did you hear that?" Suddenly, the box flashed green and a quiet whispering came from inside. The message was unintelligible, but all three felt that they had just started something that could no longer be stopped. Ola reached her hand towards the lock, trying to decipher the symbols engraved on it. Before they could do anything, however, they heard someone's footsteps behind them - definitely belonging to someone who was not one of them....