A chilling silence pervaded the underground sewer tunnel.
Red mist crept in through cracks in the walls and vents, covering the floor like a thin film.
Whenever the mist rippled across the knee-deep stagnant water, blurred red shadows wavered on the damp concrete walls.
The clammy air carried a faint stench of mold and metal that pricked at the nose.
Jeong Hae-jun's eyelids fluttered faintly where he lay sprawled on the floor.
He let out a ragged breath as he came to. How long had he been out?
A hazy memory surfaced: the moment when the red mist's hand struck him and sent him sprawling.
His entire body felt glued to the ground, but he gritted his teeth and forced his fingers to move.
The cold water and rough concrete under his fingertips brought a faint sense of reality back to him.
He slowly pushed himself up.
His ears still rang, and his head throbbed as if it might split open.
His surroundings were blurred by red mist.
Just moments ago he'd heard his teammates shouting. Now their voices were gone—only faint, static-laced breathing came through his earpiece.
He drew in a deep breath and let it out, steadying his pounding heart.
Just then, he noticed a ventilation fan on the ceiling above.
In the dim light, the fan's blades appeared to be slowly spinning in reverse.
He squinted, suspecting an optical illusion, but the fan still looked to be turning backward.
He shook his head, trying to clear his thoughts.
It's a hallucination... focus.
He bit his lip and struggled to stay grounded in reality.
His earpiece crackled with static at regular intervals.
And a bizarre pig-like squeal repeated about every 0.8 seconds.
He couldn't tell if the sound was a signal from the specter or just equipment interference. Either way, a wave of dread washed over him.
Suddenly, the incandescent bulbs lining both sides of the tunnel flickered all at once.
As he jerked his head up, a rippling tremor came from the darkness behind him.
A low, heavy vibration traveled through the floor and into his chest.
The flowmeter's LED indicator on the wall started blinking in sync, its needle swinging wildly.
As if in response, the tunnel itself seemed to warp—stretching out and then snapping back in a surreal illusion.
"Waaah... waaah..."
A child's wail echoed through the tunnel.
Jeong Hae-jun instinctively swung his flashlight toward the sound.
At the far end of its faint beam, the opening of a side tunnel came into view.
Detective Choi Do-yoon stood at the entrance, deathly pale and frozen in place.
As if hypnotized by the eerily familiar child's cry, Choi Do-yoon began stumbling into the side tunnel.
"Detective Choi, is someone there?!"
He called out, but Choi gave no response and continued trudging deeper inside.
Suddenly, the water at Choi's feet seemed to gush upward, an impossible sight that made him stumble.
He caught himself against the wall, but still he shuffled forward, drawn by the disembodied crying.
Meanwhile, from the opposite side in the deeper darkness, he heard Detective Yoon Tae-sik let out a choked groan.
"This... this can't be..."
Yoon stared at a teammate's silhouette just a few steps away—but somehow it looked exactly like someone he'd lost years ago. The figure lurched toward him, its face a bloodied mask. The sight felt so real that Yoon's mind reeled in horror.
Yoon raised his sidearm instinctively, his eyes wild with fear and fury.
"Back... off...."
His voice quavered in warning, and his finger slowly tightened on the trigger.
Suddenly, intense anxiety crashed over Jeong Hae-jun. If none of them were in their right mind, they could end up shooting each other by mistake.
"Everyone, snap out of it!"
Jeong Hae-jun bellowed.
But his shout was lost amid the echoing rush of water and never reached the others.
He could only faintly see his teammates stumbling in the red mist, each seemingly trapped in a nightmare.
At that moment, a metallic clatter came from the maintenance hatch above—someone was climbing down a ladder.
"Detective Park?!"
He swung his flashlight upward and saw Detective Park Jae-min coming down, a gas mask over his face.
Park Jae-min scanned the area with a thermal camera on his belt, but its screen showed only static and blurry shapes.
The heavy moisture in the air scattered the infrared and rendered the device ineffective.
Instead, he swept the surroundings with his own eyes.
Through the red mist, he spotted a warning light blinking next to the flowmeter.
It flashed at a steady interval—around every 0.8 seconds, Park realized.
"The alarm light... 0.8 seconds... that's it!"
Park muttered. Then he pressed his radio and barked, "Visibility's no good... thermal's out... flowmeter alarm light blinking 0.8 seconds... sync on it..."
His transmission crackled with static, but Jeong Hae-jun caught the key words.
Alarm light... 0.8 seconds... sync.
He understood at once. If everyone moved in time with the blinking light, they could gauge each other's positions.
"If you can hear me, pair up back-to-back!" he ordered over the radio.
His voice broke up in static, but the meaning seemed to get through.
He held his flashlight aloft and flashed it in sync with the alarm.
In the distance, two beams flickered back almost simultaneously.
Yoon and Park had gotten the signal. But Choi's light was still nowhere in sight.
He quickly pulled out a spare flashlight and dropped it on the floor.
He hoped that if Choi was lost, he'd see that light and follow it.
He pressed the radio again and continued giving orders.
"Secure a light source and meet at the central sump!"
Just then, loud splashes echoed—beyond the mist, a panicked figure bolted past.
One of the support team, terrified, sprinted toward the exit.
"Wait, don't—!"
Before anyone could stop him, the terrified man dashed into the red mist, and in an instant he was gone. A heartbeat later, a heavy boom echoed as a metal floodgate slammed shut.
The warning light on the wall flashed red, painting the tunnel in a cold glow, and a shrill siren blared.
Beyond that gate was now completely sealed off.
For those left behind, the brutal reality hit with icy finality: he wasn't coming back.
"Dammit..."
He cursed under his breath.
Beyond the closed floodgate, the red mist swirled like a vortex.
His distant screams and gasps came through the radio for a moment before static swallowed them.
A cold tension dug even deeper into the remaining team.
Jeong Hae-jun gritted his teeth and steadied his racing heart, then looked down.
A yellow line on the floor marked the path to the central sump.
He aimed his flashlight along it and began to run.
Far ahead, the flowmeter's alarm light still winked steadily at 0.8-second intervals.
He sprinted through the darkness, matching his steps to its tempo.
Just then, a second wave of hallucination hit.
The ceiling bulbs sparked and flickered in rapid succession.
The red mist surged upward as if alive, then whipped into a furious vortex.
Every stain on the walls glowed with a blood-red afterimage that overwhelmed his vision.
At the same time, his earpiece erupted with overlapping voices.
"...Here... anyone... respond... help..."
He gritted his teeth and pressed a hand over his earpiece.
The chaotic noise filled his head, but he forced himself onward.
A moment later, a broad domed space opened up before him—the central sump chamber.
He stumbled in, gasping for breath.
The chamber was broad and the ceiling high—a relatively open space.
But even here, thick red mist hung in the air.
The water pooled in the huge central basin was calm in reality—yet to Jeong Hae-jun's eyes, blood-red waves were roiling within it.
As he caught his breath, he swept his flashlight around. There—a shadow flitted across the curved wall.
He quickly swung his gun toward it. At that moment, a huge shape began unfurling high on the wall.
Something emerged from the red mist, roughly human in form. All he could discern were two glowing red points for eyes and the outline of limbs unnaturally long.
Jeong Hae-jun's heart slammed. At last, the specter had revealed itself—the very being behind the red mist.
It moved slowly, almost crawling along the wall.
He immediately snatched the flashlight from his belt and, recalling Park's advice, flashed it in time with the alarm's 0.8-second pulse.
With each strobe of light, the massive silhouette flickered, its outline fading for a split second.
It's working.
Now he was sure—a steady light source or electromagnetic interference could crack the specter's illusions.
He barked into his radio with a final order.
"Everyone, lure it to the center of the sump! Stay in pairs!"
His voice rang out across the chamber.
Simultaneously, he dashed to a ladder at the chamber's edge and raced up toward the ceiling.
He climbed up to the ventilation grate near the ceiling, almost eye-to-eye with the specter.
At that moment, the specter whipped its head around, fixing two blazing red eyes on him.
Its limbs were spread wide, clinging to the wall like a human-shaped spider.
The creature opened its maw, unleashing an ear-splitting roar.
"Graaaah—!"
At that instant, the alarm blared once more—the one by the floodgate where the support member had vanished.
Even as the deafening siren cut through the air, he didn't so much as blink, locking eyes with the specter.
Now's my chance.
He drew a breath and tightened his grip on his pistol.
Then he kicked off and leaped down into the chamber's center, rolling as he hit the ground.
His body cam was recording the massive form in the crimson darkness.
He clenched his jaw, determined not to miss a single detail. He seared every detail of the creature into his memory: its height, its unnaturally long limbs, its slightest movement.
In the next instant, the enormous shape hurtled toward him through the red mist.
A claw-like shadow scythed at his face, but Jeong Hae-jun stood his ground and met it head-on, a rough breath bursting from his lungs.
In that moment, a blinding crimson light engulfed everything—