The ascent was endless. Every muscle burned until it felt like shaking jelly. The glossy bck obsidian of "The Throat" slowly gave way to something familiar but no less eerie: ancient, crumbling brick. Far below, the Substrate’s bioluminescence faded, leaving them in a thick, suffocating darkness that Mateo’s weakening fshlight could barely pierce.

  The air shifted. The sterile static was gone, repced by the heavy, damp stuffiness of forgotten dungeons. Wet brick grit and bitter, iron-tasting dust crunched between their teeth. Millions of tons of concrete—Avenida Rivadavia—pressed down from above, a blind monolith of human chaos where every heavy step they took echoed like a dull pain in the city's cold arteries.

  — “We’re going up,” Mateo said hoarsely. He checked the compass on his watch. The needle had finally stopped spinning like crazy and now pointed north with a trembling jerk. “Based on the slope, we’re heading directly under the avenue.”

  — “Rivadavia?” Nico asked, breathing hard. He wiped his soot-stained face with the torn sleeve of his knock-off tracksuit. “So we’re right under Congress? There should be grates. Exits. Anything to get the hell out of here.”

  — “Don’t get ahead of yourself, turro,” Cobra snapped, though her voice shook with exhaustion. “Find a dder that doesn't lead straight into that thing’s mouth first.”

  Suddenly, the sloping tunnel ended in a crude breach. A hole with jagged, torn edges—as if punched through from the inside by a giant fist—led into a wider, man-made space. They scrambled over a high pile of broken brick, kicking up clouds of century-old dust that settled on their sweaty faces like bitter ash.

  They stopped dead.

  They were standing on tracks. But this wasn't the modern subway with its smooth concrete sleepers and bright lights. The rails here were thinner, covered in scales of rust, and the sleepers were made of bck quebracho wood soaked in heavy oil. The walls were lined with dull, cream-colored tiles featuring a burgundy geometric pattern along the edges. The silence wasn't absolute—it vibrated.

  — “I know this pce,” Cobra whispered. She walked to the wall and ran a finger over the ceramic, wiping away a thick yer of soot. Beneath the sticky grime, an old hand-painted ad emerged: a strange, frightening head of a man with nails, pins, and corkscrews sticking out of his skull.

  Below it, elegant script read: Geniol corta el dolor. — “Geniol,” Leo read, squinting in the fshlight's beam. “A headache ad. From the thirties. I saw these in old archive photos.”

  — “This is the Alberti Norte ghost station,” Mateo said, recognizing the old architecture. “They closed it in ’53 because it was too close to Pasco station.”

  Suddenly, the wall to their left vibrated. A growing hum filled the air, and then, just inches behind the yer of old brick, a train roared past. Light from the car windows flickered through narrow technical slits, catching their pale faces in the dark.

  — “Trains pass it every day,” Mateo continued, shouting over the din. “Just three feet behind this wall. But the passengers only see flickering shadows. None of them have any idea that an abyss has opened up right beneath them.”

  As the train noise faded, a faint rustle came from the darkness of the high vaults above. The sound of falling pster. Mateo spun around, instinctively shielding the kids with his body.

  Cobra drew her street bde in a fsh. A figure descended silently from the ceiling on a thin, almost invisible bck cable. A bck, form-fitting tactical suit, a massive night-vision device, an assault rifle across the chest. The figure touched the floor softly, rolling into a crouch before standing up. Cobra lunged, ready to strike, but the figure raised her hands, palms out.

  — “Friendly.”

  The voice was female. Famously familiar, a sound that caused a physical ache in Mateo's ribs. The stranger flicked the tches and pulled off her tactical mask and goggles. Green eyes burned in a soot-stained face.

  — “Elena?!” Mateo dropped the heavy metal pipe he had picked up for defense. It cnged against the rail. “Elena, how... how the hell did you find us in this crypt?”

  Elena unclipped her carabiner. She moved with a frightening, predatory grace. Right now, she didn't look like the logistics manager of a transport company he had shared a bed with for the st twenty years. She looked like a soldier. A perfect gear in a ruthless machine.

  — “I put a tracker on Leo’s phone a year ago,” she said, stepping toward them. “Sorry. Paranoid mother's instinct. The signal cut out near the club on Sarmiento. From there, I just followed the trail of structural damage in the drains.” She looked at her husband. Her gaze was a thick mix of guilt and relief. “I came down through the Line A vent shaft. Sigma is combing the upper levels now. They think you all died in the cave-in. Luis is already writing the obituaries.”

  — “A bug?” Mateo’s eyes darted from her face to the professional assault rifle and tactical vest. “A logistics manager pnts a tracker and enters an abandoned subway with a machine gun? What the hell is going on, Elena?”

  — “Your only chance of survival is what's going on, Mateo. Think of logistics as just knowing how to deliver cargo from point A to point B on time. And right now, you are the cargo. You want an interrogation? Get out of this grave first. Dale, move!”

  She turned her gaze to her son. Leo stood leaning against the cold tile, deathly pale, his eyes dark pits. Elena rushed to him, pulled off a tactical glove, and took his hand. Seeing her son's bckened, ink-stained fingertips, she sucked in a breath and pressed her lips into a thin, bloodless line. She said nothing. She didn't need an expnation. Her files contained reports on what IT does to those who connect to its memory.

  — “We have to go,” her voice turned icy and professional. “It’s not safe here. The system’s mutation is accelerating. Vargas is just the beginning of the immune response.”

  — “Where to?” Mateo asked, forcing himself to think logically. “Into the tunnel toward Congress? We can break the grates.”

  — “No. There are motion sensors and a sweep squad on duty there. We need the dead end.”

  — “The dead end?” Nico ughed nervously. “Mrs. Terminator, with all due respect, that’s a solid brick wall. I grew up here. I know the subway.”

  — “It’s not a wall, Nico,” Elena checked her rifle’s magazine in one professional motion. “It’s Line F.”

  — “Line F is an urban legend,” the boy snorted, gncing at Cobra. “Diggers know it doesn't exist. Those are stories for rich tourists and schizos.”

  — “In intelligence, legends are often just files with the highest secrecy clearance,” Elena smirked, but the smile didn't reach her cold eyes. “In the seventies, when the military was in power, they started digging a secret tunnel from Casa Rosada to the Campo de Mayo barracks. To move troops underground in case of an uprising. But they hit this. An existing network. They sealed all city-side entrances with thirty-foot concrete plugs to hide the find, and turned the network into their own private testing ground.”

  They moved deeper into the abandoned station, toward where the rusty rails ended in a giant heap of packed construction debris. But Elena knew where to look. Behind the debris, hidden in the shadow of a massive arch, a passage appeared.

  And in that passage stood a train car.

  It was one of the legendary Belgian La Brugeoise cars—"Las Brujas" (The Witches), as the people lovingly called them. Elegant wooden cars with crystal mirrors, carved panels, and brass handrails that had carried porte?os for nearly a century until they were retired in 2013. This car hadn't been scrapped. It had been walled up here in the void. And it had changed.

  — “Holy mother of...” Mateo whispered, shining his light on the side of the car.

  The polished red mahogany siding had sprouted. Through the exquisite woodwork, tearing through copper rivets, thick bck veins of the SUBSTRATE were pushing through. The organism was using the human transport as a convenient frame, wrapping around it like a predatory, thinking ivy. Under the fshlight, the wood looked soft, pulsing—frighteningly simir to fyed flesh. The window gss had turned cloudy, covered in a whitish film like the cataracts of blind, dead eyes. The doors were ajar, forming a gaping maw inside which bioluminescent nodes contracted rhythmically.

  — “Symbiosis,” Mateo noted with a scientific coldness he used to mask his growing primal terror. “The Substrate doesn't destroy matter. It assimites it. Wood, metal, even human bone... to it, they're just building materials. It looks like IT isn't destroying reality, but... redesigning it. Like it’s building its own world using our debris as a foundation.”

  — “And we have to go through it,” Elena said quietly, aiming her rifle into the dark interior of the car. “There’s no other way to Line F.”

  Mateo stepped abruptly to the side, blocking his wife's path to the open doors.

  — “Are you out of your mind?” his voice broke into a ringing whisper. “You’re suggesting we voluntarily climb into this thing’s esophagus? Look at it! It’s pulsing. The wood has grown roots into the metal.”

  Elena didn't lower her weapon. Her face, in the greenish light of the tactical fshlight, looked carved from cold stone.

  — “This is the Substrate’s only blind probe in this sector, Mateo. An organism doesn't attack what it’s already digested. Inside the car, we’ll be dead weight to the system. A piece of rotting wood. Sigma has blocked all the usual junctions; they’re coming here with fmethrowers. Choose: burn alive at the hands of my former colleagues or endure five minutes of nausea.”

  Nico spat nervously on the rails, but the saliva hung in a thick thread in the heavy air, never reaching the ground.

  — “Ni en pedo,” the boy from Vil 31 hissed, backing away from the car’s gaping maw. “Not for any amount of money, posta. I’m not going in there. I’d rather go back to Vargas and die by a bullet like a normal person, not as food for a giant caterpilr.”

  Cobra grabbed him hard by the colr of his jacket, pulling him close.

  — “Vargas is part of this shit now, idiot. He’ll tear you to shreds faster than you can pull your street bde. Stop whining. Follow the crazy dy with the gun.”

  Mateo turned the fshlight beam back to the car. The old Belgian "Witch" looked like a fallen monument to a bygone era. Once, its polished mahogany had reflected the smiles of hundreds of thousands of people rushing to work, to dates, to the movies. Now it sang the dull, silent song of forgotten passengers, rooted forever to the rails, transformed into the slow-beating, weary heart of the underground.

  Leo walked slowly toward the car. Before Mateo could stop him, the teenager touched the copper handrail entwined with bck veins. His bckened fingertips glowed faintly, syncing with the car's rhythmic pulsation.

  — “IT isn't aggressive,” Leo said hollowly, without turning around. The double, synthetic echo in his voice was becoming clearer. “IT is just breathing. It’s a membrane. If we don’t resist, IT will let us pass.”

  — “Behind me. Step where I step,” Elena commanded, stepping into the darkness of the car.

  From the depths of the wooden womb came a low, wet sound—like a deep, ragged exhale. The "Witch" was waiting for its passengers.