The thing outside vanished.

One moment it was there, a pale smudge in the deep-sea gloom, and the next, it was swallowed by the darkness. Kaizoo stood frozen, his knuckles white where he gripped the back of the pilot's chair. The only evidence it had ever been there was the primal fear now lodged in his throat, cold and solid.

Was it real? The question was a trap. If it was real, he was prey. If it wasn't, his mind was already breaking—a equally terrifying prospect at eight hundred meters below the surface.

A new sound ripped him from his paralysis.

Tssssss—

It was a high-pitched, desperate hiss, like a tire deflating at a thousand atmospheres of pressure. A jagged red icon flashed to life on the main console: HULL BREACH. MINOR. SECTOR 4-A.

The airlock. The small, external compartment.

Kaizoo’s training—the ghost in his machine—kicked in. He slapped a button, bringing up the internal structural schematic. A small section near the stern was blinking crimson. It wasn't a catastrophic rupture, not yet. It was a pinhole leak, likely in a coolant or air-filtration pipe, but at this depth, a pinhole was a promise. A promise that the immense, crushing weight of the ocean would patiently, inexorably, widen it until the Nautilus-07 imploded into a fist-sized ball of scrap metal.

“Oxygen levels at nineteen percent. Hull integrity compromised,” LUNA’s voice announced, as placid as a pond.

"Shut up, I know!" he snarled at the ceiling, his voice raw.

He had to get to Sector 4-A. He lurched toward the rear of the cabin, his movements clumsy in the confined space. The maintenance locker was sealed with a manual wheel. He spun it, the rusted mechanism groaning in protest, and yanked the door open. Inside, neatly stowed, was a basic repair kit: a sealant gun, epoxy (high grade putty), and a wrench. The tools felt familiar and alien in his hands.

The access hatch to the airlock chamber was a round, heavy door set into the floor. He heaved it open, the metallic clang echoing. A short ladder led down into the cramped, cylindrical space. It was even colder here, the air smelling sharply of ozone and sea.

Tssssss—

The sound was louder now, a vicious little serpent in the dark. A fine, freezing mist of seawater sprayed from a joint in the wall, soaking his sleeve instantly. The pressure was forcing the water through, atomizing it. He could feel the vibration in the metal, a constant, terrifying hum of unimaginable force held at bay by a few centimeters of steel.

He had to work fast. His fingers, numb with cold and fear, fumbled with the sealant gun. He loaded a cartridge of fast-setting polymer and pressed the nozzle against the leak. The hissing intensified for a moment, fighting back, before the thick gel began to fill the breach. He squeezed the trigger, watching the white paste spread and harden under the spray.

It was as he was applying a second, reinforcing layer that his headlamp swept across the interior wall of the chamber. And he saw it.

Next to the leaking pipe joint, on the dull grey metal, was a mark. It wasn't a scratch from equipment or a weld seam. It was a set of five long, parallel grooves, dug deep into the steel. And within those grooves, etched into the metal itself, were the faint, swirling patterns of fingerprints.

A handprint.

But it was wrong. The placement was all wrong. It was too high, and the fingers were splayed at a desperate, broken angle. It looked less like someone bracing themselves, and more like… someone had been trying to claw their way out from the inside of the wall.

---

The sight of the handprint sent a jolt of pure, undiluted horror through him, short-circuiting his fragile focus. For a moment, the only sound was the frantic hammering of his own heart and the dying hiss of the leak.

Focus. Or you die.

He tore his eyes away from the ghastly mark and finished his work, slapping the epoxy putty over the sealant with frantic slaps of his palm. He worked until the hissing stopped, replaced by a solid, reassuring silence. He ran a hand over the patch. It was cold and firm. For now, the ocean was held back.

He scrambled back up the ladder into the main cabin, his clothes soaked and clinging, his body trembling from adrenaline and cold. He slammed the access hatch shut and spun the wheel, sealing the nightmare of that chamber away. Leaning against the cold metal, he tried to steady his breathing.

“Hull breach sealed. Oxygen levels stable at eighteen percent,” LUNA reported.

Stable. But critically low. He had bought time, not salvation. He looked at the radar screen. The two blips were still there, the close one pulsing softly, mockingly. The note—Do not turn back—felt more like a command now.

He had to make a choice. He had to move.

His hand moved towards the engine ignition sequence. He would go to the distant signal. It was the logical choice. The safe choice.

Knock.

The sound froze him mid-reach.

It wasn't a groan of metal or a hiss of hydraulics. It was a clean, sharp, unmistakable sound.

Knock. Knock.

Three impacts. Hard, deliberate, and rhythmic. They came from the outer hull, right next to the main viewport.

Someone—or something—was knocking.

His blood turned to ice. He stood perfectly still, not even daring to breathe, his eyes locked on the blackness of the viewport.

Silence.

Then, driven by a madness he didn't understand, his own hand, moving as if possessed, lifted and rapped his knuckles three times against the interior wall.

Knock. Knock. Knock.

A pause, thick and heavy with anticipation.

And from the other side of the hull, the answer came immediately, sharp and clear.

Knock. Knock.

---

(A note from the author):

Well, that took a turn! Nothing says "welcome to the neighborhood" like a friendly knock on the door... when you're hundreds of meters underwater. 😅

Knock, knock.

Who's there?

Not the pizza delivery guy, that's for sure.

I hope the chills are a good kind! If you're enjoying the deep-sea nightmare so far, a vote, comment, or add to your library would be amazing! It helps more readers find the story and tells me you're as hooked as I am.

I'm dying to know:

· What (or who) do you think is knocking?

· Would you have been brave enough to knock back?

Thanks for diving deeper into the mystery!

[MKI]