The old villa at the end of Park Street had stood empty for years. Its windows were obscured by heavy curtains, and a rusty bell hung on the handle of the front door that rang out at the lightest touch. When Lena and her parents moved in there at the beginning of the summer, the girl felt both excited and slightly anxious at the same time. Their first few days were spent unpacking cardboard boxes and exploring new nooks and crannies of the house. Lena had her own big room upstairs and carved balustrades to run down, feeling like the heroine of her favourite novels. One morning, with the sun barely breaking through the overgrown garden, Lena decided to take a look at the attic. Climbing up the creaking stairs, she came across a small box in the corner of the room. Inside she found a brass key, strangely heavy, with an intricate design on the head. - Look what I found! - she bragged in the afternoon to Majka and Oskar, her two best friends. - 'Maybe it fits one of the doors in the house,' suggested Oskar, rubbing his hands together excitedly. The three friends decided to test the key. They searched the ground floor, the basement and finally the first floor. Finally, Lena remembered a small door in a narrow corridor at the end of the hall. The door was almost invisible, blending into the dark grey wall, and above it was a cracked plaque with a blurred inscription. The key fitted perfectly. The lock squeaked draughty and the door swung open, revealing a staircase winding downwards. The staircase was lined with stone slabs and dusty old portraits hung on the walls. Lena, Majka and Oskar looked after each other nervously, but curiosity was stronger than fear. They walked slowly down the stairs, holding hands. Downstairs, a windowless room awaited them, but full of books, pictures and... something else. In the middle stood a box wrapped in a silvery cloth, as if someone had recently left it. From within it came a subtle, pulsating sound, reminiscent of a heartbeat. There was a smell of dust and something unfamiliar in the air that made the children's skin suffer with anticipation. Lena was already reaching out to lift the lid of the box when suddenly a quiet whisper came from behind the wall. The friends froze, holding their breath, listening to the disturbing sound....