Chapter 1:

The clock struck 11:45 PM. Han-young High School was as silent as a graveyard.

Se-yeon, Min-ah, Ji-woo, and Hana—four best friends—had lost track of time while studying late in the library. When they finally looked at the clock, horror struck them. School hours were long over.

"Hurry up! If the security guard catches us, we are dead," Se-yeon said, grabbing her backpack.

The four girls rushed down the dark stairs to the ground floor. But when they reached the main exit, their hearts sank. A heavy iron chain and a massive padlock barred the doors. The school was completely locked from the outside.

"No, no, no! We are trapped!" Min-ah whimpered, tears welling up in her eyes as she grabbed Hana’s arm.

"Stop crying, Min-ah! Hana, get your phone out and call the police," Ji-woo commanded, trying to hide the panic in her own voice.

Hana unlocked her phone with trembling fingers, but her face went pale. "There's no network... zero signal!"

Suddenly, the school’s automatic PA speakers crackled to life. Screeech...

A heavy, distorted sound of breathing echoed through the empty corridors. Then, a row of metal lockers down the hallway began to rattle violently, as if someone—or something—was trapped inside, screaming to get out.

BANG! BANG! BANG!

The girls screamed and huddled together, holding onto each other for dear life.

At that exact microsecond, all four of their phones buzzed simultaneously. A text notification lit up their screens from an unknown number. It was the same message sent to all four of them:

'Welcome to the Night Shift. The game begins now. If you want to survive until sunrise, do not look back.'

Right at that moment, from the darkness directly behind them, came the wet, squishing sound of bare footsteps...

Squish... squish...

Se-yeon's heart pounded against her ribs. She gripped Ji-woo's hand so tightly her knuckles turned white. The freezing cold draft on the back of their necks became unbearable. It smelled heavily of old, rotting lake water.

"Don't turn around," Se-yeon whispered, her voice barely audible. "Whatever you do, keep looking at the door."

But the footsteps stopped exactly behind Min-ah. Min-ah began to shake, her eyes fixed on the glass window of the locked main door. In the dark reflection of the glass, she saw something that made her breath stop.

Standing right behind them was a tall shadow. Its arms were unnaturally long, dripping with dark water, and its head was tilted at an impossible, broken angle. In the reflection, its pale, featureless face suddenly twisted into a wide, terrifying grin.

"Run!" Ji-woo screamed, breaking the silence.

The four girls didn't look back. They sprinted toward the main staircase, their shoes squeaking against the polished floor. Behind them, a loud, bone-chilling shriek echoed through the corridor, followed by the sound of something dragging its heavy, wet body up the stairs at an unbelievable speed.

They scrambled up to the fourth floor, desperate to find a place to hide. Every classroom door they slammed their hands against was tightly locked. The footsteps were coming up the stairs.

Then, at the very end of the dark hallway, the door to Classroom 4-B slowly creaked open on its own, revealing pitch-black emptiness inside.

With the terrifying sounds closing in, the girls ran inside the room and slammed the door shut, locking it from the inside. They collapsed onto the floor, trembling in the dark.

Their phones buzzed again in perfect unison. A new message appeared:

'Rule #1: You are temporary safe inside Classroom 4-B. But do not answer the door, even if it sounds like a voice you know.'

Suddenly, three slow, loud knocks rattled the wood of the classroom door.

Knock... Knock... Knock...

From the other side, a tearful, terrified voice called out. "Girls? Please open the door... It's me, Hana. I got left behind in the corridor! Please let me in, it's right behind me!"

Se-yeon's blood ran cold. She slowly turned her head in the darkness. Hana was sitting right next to her, holding her own phone.

If Hana was inside the room... who was crying outside the door?

The voice outside the door didn't stop crying. "Please, Se-yeon... Min-ah... open up! It's getting closer to me!"

Min-ah shrunk back into the corner, clenching her teeth to prevent herself from screaming. She kept switching her gaze between the door and the real Hana sitting right beside her. The real Hana was frozen, staring at the shattered glass panel of the door with terror.

Suddenly, the sobbing stopped. The entire hallway fell deathly quiet.

Then, a sickening wet sound echoed through the silence. Squish... splat...

Through the broken glass panel of the door, a long, bone-white hand slowly slid inside. The skin looked swollen and gray, dripping with cold, slimy black water. The fingers had sharp, dirty nails that scratched wildly against the inner wooden surface of the door, searching blindly for the lock handle.

Scratch... scratch... scratch...

"It's going to open it!" Ji-woo whispered, her voice trembling as she looked around for a weapon. She grabbed a heavy wooden chair from the front desk. "If that thing gets in, we are dead."

"Wait!" Se-yeon pulled Ji-woo's arm, her eyes fixed on her phone screen which was vibrating again. Another text message had just popped up from the unknown number.

'Rule #2: The Mok-so-ri (The Mimic) cannot tolerate bright light. The main light switchboard is right next to the classroom door.'

Se-yeon looked at the switchboard. It was barely two inches away from where the terrifying, pale hand was currently swinging and scratching the wall. To turn on the lights, someone had to run right into the danger zone.

"I'll distract it," Ji-woo said, her grip tightening around the wooden chair. "Se-yeon, the moment I hit it, you flip the switch."

Before anyone could stop her, Ji-woo rushed forward and slammed the heavy chair directly onto the pale, wet hand.

CRASH!

A horrific, inhuman shriek pierced through the classroom. The hand twisted at an impossible angle, but instead of pulling back, the fingers suddenly lunged forward and tightly wrapped around Ji-woo's wrist!

"Ji-woo!" Hana and Min-ah screamed in unison.

The entity outside began pulling Ji-woo toward the broken glass panel. Ji-woo struggled with all her might, her shoes sliding against the dusty classroom floor.

Se-yeon didn't waste a single second. She lunged forward, dodging the snapping fingers of the monster, and slammed her palm against the main light switch.

Click.

The bright fluorescent tube lights of Classroom 4-B flickered twice and burst into a blinding white glow.

The monster outside let out another deafening scream. The pale hand immediately released Ji-woo and snapped backward through the broken glass, disappearing into the dark corridor.

Ji-woo collapsed onto the floor, coughing and holding her bruised wrist. The classroom was now brightly lit, but the girls knew they couldn't relax.

Hana’s phone buzzed once more. It was a picture message this time.

With shaking hands, Hana opened the image. It was a live photo of the back of their own heads, taken from the high ceiling corners of Classroom 4-B. Attached to the photo was a short text:

'Rule #3: The lights will only stay on for 5 minutes. The game has just entered Phase 2. Find the hidden key before the darkness returns.'

Chapter 3: The Five-Minute Hunt and The Double

"Only five minutes!" Hana panicked, holding up her phone screen with shaking hands. Her fingers were trembling so violently that she almost dropped the device. A terrifying countdown timer was ticking down right before their eyes on the bright display—04:59... 04:58... 04:57... Time was slipping away like cold water.Ji-woo held her bruised, painful wrist tightly and forced herself to stand up against the wall. "We need to find that hidden iron key no matter what happens. If the darkness returns to this room, that monster will definitely try to get inside again. We won't survive a second time."Se-yeon quickly scanned the entire messy classroom. The room was huge and filled with obstacles. It had over thirty broken wooden desks, a large teacher's platform, an old tall wooden cupboard in the corner, and a big notice board at the very back. The key could be hidden anywhere in this mess."Min-ah, you and Hana check inside the student desks right now! Ji-woo, you and I will search the teacher's desk and the old cupboard. Hurry, we don't have time!" Se-yeon commanded loudly.The four girls tore through the room in absolute panic. The digital timer on the screen was dropping incredibly fast—03:12... 03:11...Hana and Min-ah checked inside the wooden desks one by one, throwing their hands deep into the dark, dusty compartments. Old forgotten books, thick layers of grey dust, and creepy spiderwebs came flying out into the air. "There's nothing here! It's completely empty!" Min-ah cried out, her young voice cracking with pure fear.Meanwhile, Se-yeon ripped open all the locked drawers of the teacher's desk with brute force. There was nothing inside except old white chalk and pieces of attendance registers. She quickly turned around and yanked open the doors of the old wooden cupboard. A foul, rotting smell immediately hit her nose—it was the exact same sickening scent that had come from the monster's cold hand.The timer was now at 01:30. The fluorescent tube lights on the ceiling suddenly began to flicker violently, threatening to shut off and leave them helpless."We have to hurry up!" Ji-woo shouted loudly, tossing out old papers and files from inside the smelly cupboard. Finally, at the very bottom corner, her hand hit something solid. She spotted a small iron box. "Se-yeon! Look at this!" Ji-woo pulled the heavy box out. It was securely locked with a four-digit combination pad."What could the password be?" Hana asked, running over to them. Her phone vibrated violently again. The timer was down to just 45 seconds. A final clue from the unknown mysterious number appeared on her screen: 'The price of betrayal is always zero.'Se-yeon's mind raced through the clues. "Betrayal... zero... and this room is Classroom 4-B!" she gasped loudly, her eyes widening. "Number 4 means death in Korea, and the student from the school's past was betrayed right here in this room!"Se-yeon quickly spun the plastic dials on the lock, entering the secret numbers: 4 - 0 - 4 - 0.CLACK.The lock snapped open beautifully! Inside lay an old, rusted iron key. "I found it! I actually found it!" Se-yeon grabbed the cold key. At that exact microsecond, the countdown timer hit 00:00.BZZZ... CLICK.The bright lights in Classroom 4-B died instantly. The room plunged back into a heavy, freezing darkness.But the silence didn't last. From the other side of the broken glass door, Se-yeon’s own voice echoed, giggling creepily. "Did you find the key, friends? Now open the door for me..."Min-ah squealed loudly, covering her ears in horror. "Se-yeon... why does it sound exactly like you?"Se-yeon gripped the cold iron key in her uniform pocket, her mind racing. "Because it's a dangerous trap. It wants us to panic. Don't listen to it."Suddenly, Hana’s phone buzzed again in her hand. The screen's faint glow lit up their pale, terrified faces. A brand new text message from the unknown number appeared:'Rule #4: The Mok-so-ri cannot enter through a locked door on its own. But it will try to make one of you turn against the others. Do not leave anyone behind.'"Look over there!" Ji-woo whispered sharply, pointing toward the front door. Through the faint moonlight filtering through the window, they saw the large shadow outside shift. It wasn't trying to break the door handle anymore. Instead, it was slowly crawling up toward the open window gap above the door frame.Slither... squish..."It's trying to climb over the top!" Hana panicked."The back exit," Se-yeon said, pulling her friends up. "There is an old emergency exit door hidden right behind the teacher's blackboard. The key must belong to that!"They scrambled through the dark toward the front blackboard. Se-yeon's hands shook violently as she felt around the dusty wooden wall behind the board. Her fingers hit cold metal. A small, hidden iron door. She shoved the rusted key into the tight lock.Creeeak... Click.The lock turned, and the heavy wooden panel slid open, revealing a narrow, pitch-black emergency staircase leading downwards."Go! Go! " Ji-woo urged, pushing Min-ah and Hana inside the dark opening first. Just as Se-yeon was about to step through, a freezing, wet hand grabbed her ankle from the darkness of the classroom floor. The grip was like heavy ice, pulling her backward onto the dusty floor."Se-yeon!" Ji-woo screamed, turning back in terror.In the dim light of Hana's phone, they saw the horrible entity. It had dragged its long, twisted body halfway through the broken door panel. Its face was still a blurry shadow, but its milky white eyes were fixed right on Se-yeon. And then, it spoke again. But it didn't use Se-yeon's voice this time. It used Min-ah’s voice, crying out from the hallway, "Help me! I'm still out here!"Ji-woo looked down at the staircase where the real Min-ah was standing, and then looked back at the monster. The psychological game was tearing them apart. Se-yeon kicked wildly with her free leg, hitting the monster's cold wrist. "Ji-woo, smash the door panel! Shut it now!"Ji-woo didn't hesitate. She grabbed the heavy wooden chair and slammed it down with all her strength onto the monster’s arm. A sickening crack echoed through the room. The entity let out a low hiss and yanked its arm back. Se-yeon scrambled to her feet, diving through the hidden door panel. Ji-woo slammed the blackboard exit shut behind them and bolted it tightly.They were now standing on the pitch-black emergency staircase. The only light came from Hana’s phone screen."Is everyone okay?" Se-yeon gasped, rubbing her bruised ankle."I-I'm fine," Ji-woo panted."Me too," Hana whispered.But no one answered from the bottom of the stairs. Se-yeon quickly grabbed Hana’s phone and shone the flashlight down the narrow staircase to check on Min-ah. The beam of light cut through the darkness, and the girls froze in sheer terror.At the bottom of the stairs, there were two Min-ahs standing side by side. They looked identical, wore the exact same uniform, and both were crying, pointing at each other. In perfect unison, both Min-ahs screamed, "Se-yeon, help me! She is the monster!"Suddenly, Hana’s phone vibrated violently. A new text message popped up on the screen, but the sender wasn't the unknown number anymore. The message was sent from Min-ah's own phone. Se-yeon looked at the message, her breath stopping entirely. The text read:'Don't trust either of them. I never made it into the blackboard door.'