Tymek and Lena hear a strange signal in Astromast, the Moon's biggest colony, and follow it toward a locked technical door that should never have opened.
Tymek was thirteen, and if there was a gate, a vent, or a maintenance hatch in Astromast, he wanted to know what was behind it. Living in the Moon's largest human colony made every day feel unusual, but that morning had started with a strange kind of quiet, as if the whole city were holding its breath.
The gravity was lower than usual, so students drifted a little too easily down the corridors of the International Space School, catching themselves on handrails and wall grips. The maths teacher had to remind everyone twice to stop pushing off the walls like they were in a game. Floating planet models turned slowly over their desks, and the tall screens along the hall shimmered with star maps and weather reports from Earth.
After lessons, Tymek found Lena in the greenhouse, where warm lights glowed over rows of tomatoes, basil, and a few stubborn purple radishes. Through the glass roof, the grey rim of Copernicus Crater curved across the Moon dust outside.
"Did Dad say anything more about the signal?" Tymek asked.
Lena tipped her watering can and frowned at a leaf. "Only that it keeps coming back. Tiny pulses. Not from the city network. Not from any ship either."
"So what is it?"
She shrugged, but her eyes were bright. "Dad said not to worry about it. Which, of course, means I started worrying immediately."
That was enough for Tymek.
By the time they reached B-zone, the air smelled faintly of synthetic cocoa from the snack kiosk, but Tymek barely noticed. Between the two oldest domes, under the walkways and service pipes, there it was again: a low buzz, so soft it felt more than heard. It seemed to thrum under the floor and inside his teeth.
Lena slowed. "You hear that too?"
Tymek nodded.
The sound led them past hangars and lab windows until they reached a metal door marked Technical Area - No Admittance. The warning sign was old, scratched, and half hidden by a strip of silver tape. Lena pressed her ear to it and froze.
"Something's moving in there," she whispered.
Before Tymek could answer, the door gave a quiet hiss and slid open a crack.
Blue light spilled into the corridor.
Inside was a narrow passage that neither of them had ever seen before. At the far end, a control panel blinked red-red-red, as if it were waiting for someone to make a mistake. Tymek tightened his grip on Lena's hand and stepped forward.
Then every light went out.
In the dark, a voice spoke from somewhere ahead, flat and clear and far too close.
"Identification required. Enter access code."
Tymek and Lena stood perfectly still, staring into the black corridor, while something unseen shifted just beyond the blue glow.