The rain drummed monotonously on the windows of the deserted high-rise building on Wspólna Street as Karina, Simon and David slipped out through the ajar emergency door. Inside, it smelled of dust and old paint, and the light of their torches cut through the gloomy corridors. Their plan was simple: to investigate the notorious Floor 13, closed for years and shrouded in legend of strange sounds coming from behind invisible doors. - Are you sure this is a good idea? - whispered Simon, biting his lower lip. - 'I'm pretty sure there's nothing interesting up there, but... who doesn't take risks,' replied Karina, criss-crossing the bent staircase railings. When they reached the thirteenth floor, they were greeted by silence, broken only by the hum of the city outside the window. David was the first to notice a strange, glittering mark on the wall opposite the lift. They approached and Karina ran her hand over the surface: the taffy was becoming cool and pulsed gently under her touch. - 'It looks like a... screen,' David muttered. - 'Or a portal,' Karina added quietly. At the same moment, the world around them trembled and their reflections in the strange sheet began to distort, to take on alien colours and shapes. A pale green light flashed behind the wall and they heard a whisper that did not belong to either of them. - Do you hear that...? - Simon asked, turning nervously. A streak of mist began to slide out of the portal, and a shadow appeared, extending a hand towards them with fingers unnaturally elongated, barely visible in the blurred light. Karina took a step forward, her heart beating like mad. What was on the other side? Who was the shadow? The portal pulsed harder and harder, as if beckoning them to pass through....