Seventeen-year-old Maks and his sister Lena follow strange lights beneath an old tenement on Długa Street, only to find a hidden room, a shadowy stranger, and a sealed passage no one should have found.
Maks stood at the dirty stairwell window and looked out into the courtyard below. The tenement on Długa Street had been there for more than a century, its cracked walls climbing toward the dark, its rusty gate groaning whenever the wind touched it. Even in daylight, the place felt half-forgotten. At night, it seemed to hold its breath.
Saturday had blurred into the first evening of summer break, but the heat had not let go of the city. The bricks still gave off warmth, and the air inside the building smelled of dust, damp plaster, and old pipes. On the steps below, Lena was curled up with a book, one knee drawn to her chest, her glasses sliding halfway down her nose. When she heard Maks come down two steps at a time, she looked up immediately.
"You’re going to check it out, aren’t you?" she asked quietly.
Maks stopped beside her. "You saw the lights too."
She shut the book with her thumb still marking the page. "Everyone’s seen them. Nobody’s just done anything about it."
For the last three nights, people in the building had been talking in low voices about flashes of light drifting from the end of the basement corridor. Not from the laundry room. Not from the boiler. From farther in, where there wasn’t supposed to be anything except a storage room full of junk and a wall no one paid attention to. The adults dismissed it as bad wiring or bored kids. The stories changed every time someone repeated them. But the lights kept coming back.
Maks adjusted the strap of his backpack. Two flashlights, spare batteries, a phone with half a charge, and three candy bars Lena had insisted on packing made the bag feel heavier than it should have.
"Could be squatters," he said.
"Could be worse," Lena replied.
He glanced at her. "That’s not helping."
Her mouth twitched, but her eyes were sharp with the same restless curiosity that always got them into trouble. She was two years younger, yet she never backed away once something caught her attention. That was the problem. And, usually, the reason Maks went with her instead of trying to stop her.
They crossed the stairwell and pushed open the basement door.
The air changed at once. It turned cold and close, pressing against their skin despite the summer heat outside. Their footsteps echoed through the corridor, bouncing off the pipes and concrete walls. Somewhere deeper in the basement, something hummed in a steady, low note, too regular to be random. Maks felt Lena move closer to his side.
The light was stronger near the end of the hall. It seeped out from beneath a half-closed door, thin and pale, as if someone inside had forgotten to switch it off.
Maks lifted his flashlight, but did not turn it on yet. He reached for the handle and paused.
"Ready?" he whispered.
Lena took a breath. "No."
"Good answer."
He pushed the door open.
Inside, the storage room looked nothing like they had expected. Cardboard boxes were stacked in uneven rows across the floor, some crushed, some tied with string, all of them marked in faded ink. Small coloured lamps had been spread among them, blinking red, blue, and green in a pattern that felt deliberate. The light made the room look wrong, like a place built out of someone else’s memory.
In the middle of it all stood a person Maks had not seen a second earlier. He rose so quickly that the chair behind him scraped loudly against the concrete. His face stayed hidden in shadow, but something metallic flashed in his hand.
On the wall behind him, the beam of Lena’s flashlight caught a drawing: a maze of jagged lines, arrows, and symbols, crammed together in a way that felt less like graffiti and more like a code.
"Who are you?" the stranger asked, his voice low and rough, almost amused. "And who sent you down here?"
Lena’s fingers tightened on Maks’s sleeve.
Then the lamps flickered violently. The hum deepened into a shiver that ran through the floor, and somewhere behind the wall there came a sharp metallic crack. A section of brick shuddered, split open, and gave way with a dull grind.
Behind it was a narrow tunnel, black as wet coal, breathing cold air into the room.
Maks stared at the opening, his pulse hammering in his throat. The stranger took one step back.
And from deep inside the tunnel, something moved.