The night over Lodz was clear, crisp from the murmur of maglevs and smelled of ozone. The red bricks of the Księży Młyn evaporated after the afternoon rain, and the tall chimneys, instead of smoke, released the soft lights of transmitters into the sky. In the former spinning mill number 3, where looms once clattered, the mirrors of the LIR-3 interferometer now trembled. Lena Prochaska, black hair tied up in a knot, hands in thin conductive gloves, leaned over the operating table. Laser beams, invisible to the eye, running in vacuum tubes were doing their thing. Oscillations so subtle that an ordinary microphone would never have captured them appeared on the screen. Lena liked this moment - the silence between the data, the air so focused, as if it was listening on its own. - 'LIR, show deviations in the band below picohertz,' she muttered. The interface nodded to her with a simple beep, and the graph began to bend into a strangely familiar rhythm. She took a deeper breath. She knew that rhythm. No, it was absurd. It was like an echo of the lullaby her father used to hum before he left to work on the helium mines on the moon. She heard it for the last time when she was eleven, and it all still seemed reproducible if you just put the blocks together long enough. - LIR, wavelet transform and directional source mapping, she said, to occupy her brain with something. A map began to appear on the big screen, between photographs of Scheibler-era bricks and overlays of GIS plans. The city pulsed with a thousand vibrations - from trains, rooftop windmills, human footsteps - and yet something of a cosmic whisper cut through the noise and arranged itself in a repetitive pattern. Slow, quiet, too precise to be random. The graph jumped and caught a direction. A semicircle. The wavefire wandered like a beacon and stopped... right over spinning mill hall number 7, less than a kilometre away, on the other side of the pond. Lena straightened up so abruptly that the chair tapped her foot on the concrete. She put down her gloves and pulled out her phone, leaving a record of the signal on the LIR-3 screen - a narrow strip of line that narrowed and widened every thirty seconds like a breath. - 'Stay awake,' she texted Oskar. - 'I've got something. Księży Młyn, seven. He wrote back immediately, as if waiting lined up into the night: - Immediately. Mantis charged. What's that? - Don't laugh. It sounds like a song from my childhood. For a second she saw her words on the screen as if they didn't belong to her. She bit her cheek and added: - And it's in the microgravity range. - That sounds like the dumbest and best idea of the week,' he wrote back. She picked up her backpack, slipped a lightweight isolation suit, a headlamp, a mini-projector, a set of sensors from the printer and batteries. On the way, she switched off the main laser, leaving the LIR-3 in listening mode. An unauthorised data dump warning flashed on the screen. Dr Rose Reszka - the supervisor of their programme - had not yet returned from the conference, but her digital seal watching over the equipment did not like surprises. Lena hissed, biting her lip. She touched the hologram and signed her student authorisation. Risk. A breath. A snap. It went off. Outside, the wind sifted through the cloak like long fingers. The lighting over the canal blinked and settled on a soft blue. To the left, against the wall of the contemporary art museum, someone was practising on an antigrav board, disappearing and reappearing in patches of light like a neon swallower. Lena passed him, descending the slippery steps. The water in the pond was as smooth as metal. On the other side rose the edifice of the "seven" - a thick-beamed hall in which night circled slowly like mist. Oskar was waiting at the side entrance, leaning against his bicycle. He had a Mantis slung over his shoulder - a folding drone with thin arms and greenish propellers that looked as if someone had designed an insect from the dreams of engineering and the nightmares of children. His hair was falling over his forehead and there was an excitement burning in his eyes that Lena knew all too well. - 'I was about to drop home,' he said instead of a greeting. - But then the girl who hears the gravity song wrote. - Stop it,' she snorted, though her lips twitched from laughing. - Do you have a spatial scanner? - Built into the Mantis. I've updated the algorithms for detecting changes in air density. Zero instructions, just intuition. - He moved his eyebrows. - What are you listening for? - This thing comes back cyclically. The pattern repeated itself five times. The window - she called it in her mind before she could stop herself - opens for about two minutes. The next peak should be at 00:17. - Do we have security sensors inside? - The museum has the night route switched off in this part, the status systems show maintenance. - She hesitated. - I don't want to sound pathetic, but if it's not a mistake, then.... - This could be something we mustn't miss,' he finished for her and raised his hand to high-five her. They clashed hands in the semi-darkness. They slipped into the hall through a narrow technical door. Inside it was cold, the smell of oil from a century ago mixed with dust and fresh paint. The row of looms set up as a display was becoming a geometric landscape in the shadows. Visitor rails, railings, boards with stories of weavers and spinners, all as if frozen in time, ready for the morning light. - A praying mantis," whispered Oskar. The drone spread its arms, whistled quietly and soared above their heads, painting greenish lines around them from the projector. Curves appeared on the grid, corresponding to the sound waves of their footsteps, soft reflections off the walls. Lena took a moment to look as she liked: at the world not as things, but as equations. - 'There,' she said after a moment, pointing to the middle of the room, where the plank floor was once dotted with oil stains and where three huge drums of white blank yarn now stand. - The fire is in motion, but this is where the curve closes. She switched on a mobile LIR reading on her wrist, synchronised via a cloud-based gateway to the lab. A time stamp pulsed on the screen: 00:15:12... 00:15:11... 00:15:10... Each number stung her eyes like a cold spark. She listened in. In the utmost silence, the hall was not silent: beams - a tapping from the wind, light bulbs - clicks, as if someone was toggling a distant switch, the air - carried something at the edge of perception, something that rhythmically dimmed and returned. Oskar set the Mantis lower, near the ground. The drone swung the sensors and released thin threads of light that wiggled through the dusty haze. These strands trembled - not from their movement, but from a twitch in space, too slow to be called a sound. - Can you see it? - He asked, suddenly serious. He could see it. A faint deflection, as if someone had taken the air in a pair of pliers and squeezed it by a millimetre, drawn on the green laser grids. The pattern resembled a standing wave, except on the scale of the room. On the veneer of the spinning drums, tiny pollen rose and fell in synchronous semitones, arranged in lines and spirals like descriptions of notes without notes. - 'We've got a minute,' Lena whispered. - 'If this is really closing in, I don't want to be in this space unprotected.' She slipped the suit over her body, fastened the collar, put on her headlamp and clipped a rope to her belt, the other end of which Oskar kept wrapped around his arm. They didn't have an evacuation plan apart from that stupid rope. And maybe that was okay. - 'Whatever it is, don't touch it,' said Oskar, for the first time sounding like someone who preferred tomorrow to today's adrenaline. - 'Sure,' she replied, although she felt like putting her hand into the thick cold she could already feel on her skin. 00:16:34... 00:16:33... That's when they heard it: not so much a sound as a pattern, low, distant modulations forming a phrase that drilled through her memories. A melody without words, longer than breath, shorter than fear. It had two repetitions and a pause, during which Lena realised that the whole room - wood, brick, dust, metal - was whispering simultaneously with her. - 'This is a signature,' she said in a trembling whisper, more to herself than to Oskar. - 'Someone here...' The word 'someone' hung as the space in the middle of the hall collapsed by a fraction of an inch, as if the floorboards had taken too deep an inhale. Mantis' laser line collapsed into an oval. Within the oval, the air thickened to a state that was neither glass, nor water, nor anything Lena knew how to name. Luminous threads redrew the edges of the phenomenon like a moving sketch. 00:16:58... 00:16:59... 00:17:00. The oval unfolded, spitting out a silent blast of cold. On the outer side, as if on the other side of the glass, something moved silently. A shape. The outline of something that responded to the rhythm of their world with its own, delayed by half a beat. Lena felt her skin break into goosebumps, as if it was her body, not her mind, that recognised first. - Lena? - the air asked. It resonated exactly from that soft boundary. The voice was hers. The way it had sounded four years ago when she had recorded the first drafts for the school competition, correct but uncertain. Oskar put a hand on her shoulder. The line between them tightened. A hand appeared in the oval, for a moment doubled as if in an imperfect mirror, stretched towards her across a thickness she did not understand. - Not the touch... - Oskar began, but the words were lost in another, deeper inflection. The spinning room groaned quietly, as if an old load had been awakened in the beams. Lena brought her hand close enough to feel, not a chill, not warmth, but a completely alien kind of presence that vibrated in her bones like a taut string. A voice - her voice - repeated her name, more clearly this time, with an accent she remembered from her childhood. And then the oval shimmered, as if something else was about to cross the threshold.