Don't go to the moon, there are gods on the far side of the moon.

When that static came from the old radio, all activity in the main control room stopped.

The power was clearly off, and the power cord was still cut in the corner, the copper wires exposed and covered in a layer of dust. Yet the old-fashioned knob still slowly crawled forward on its own, the pointer moving from 92.6 to 93.1, as if someone, unseen and separated by years of dust, had gently turned it.

"Don't touch it," Xu Wangshu said first.

Qin Lan had already ordered the cabin doors sealed, her tone colder than usual: "Everyone back off, old frequencies disabled."

Wen Zhaolin looked at the radio through the glass, his face darkening instantly: "This is the Earth-Moon maintenance frequency from the Nantianmen era. Before Nantianmen Pass, no one used it anymore."

The noise suddenly became orderly.

It's not human speech; it's a mixture of short and long sentences.

Inside the toolbox, Lin Jibai's small flashlight flashed three times, then slowly flashed twice more.

Xiaoman hugged the box tightly, her face pale: "These are the maintenance codes my dad used to use. He said you can't shout in the pipes, so you have to call someone over by tapping them like this."

Xu Wangshu immediately pulled out the old maintenance files left by Lin Wangchuan. The three short and two long lines had a simple meaning: someone was hanging upside down.

What's hanging upside down isn't a person, it's a door.

A second frequency popped up on the radio, and emergency receivers throughout the city simultaneously beeped, the sound spreading outwards along the shielding layer of the abandoned lunar ladder. It wasn't a cry for help; it sounded more like someone had pressed their ear to the outside of Earth, clumsily mimicking a human knocking on a door.

Qin Lan coldly ordered, "Cut off all old frequency bands. No one is allowed to respond."

The technicians immediately took action. One by one, the receiver arrays in the main control cabin went out, and the external nodes reported that the disconnection was complete. But the knocking sound from the radio didn't stop; instead, it seemed to seep out little by little from the walls, water pipes, and under the floor.

Wen Zhaolin stared at the spectrum: "It's not clean at all. It's not learning from radio stations, it's learning from the maintenance habits left by people."

"Explain yourself clearly." Qin Lan stared at him.

"The blind hearing group under Nantianmen did indeed use this code back then. It's not a protocol, but a way for people to confirm each other in dangerous environments. As long as there are people in this world who remember how to type it, it can learn it."

Lu Chengong cursed, "Knocking on the door like a human, and you're even being polite?"

"No." Xu Wangshu looked at the white lines that were spreading on the wall projection. "It's trying to figure out which way of knocking will make us respond subconsciously."

Lin Jibai's screen lit up.

Is it a person hanging upside down, or a door?

No one answered.

Xu Wangshu pulled up a map showing the distribution of old urban infrastructure. Each time the old radio repeated its signal, a faint white dot appeared on the map: an abandoned weather tower, a hospital underground pump room, the old broadcasting room of the space city exhibition hall, and a backup receiving well for the western suburban ground station. These dots, which were originally unconnected, were now linked together by a thin line hanging down from the far side of the moon.

Xiaoman suddenly said, "It doesn't want to enter the door; it just wants to turn the door upside down first."

Correct.

If the door is upside down, the inside and outside will be confused. People on earth may think they are saving those outside, but in reality they may be inviting things from outside to fall in.

Qin Lan ordered the radio to be physically dismantled. Just as two security guards approached, the radio went out by itself, the hands stopping at 93.1.

After a brief silence, a very faint metallic scraping sound came from the bottom of the toolbox.

Lin Jibai's flashlight did not light up.

However, a line of unfamiliar text popped up on the screen:

Please check: Is there still sound coming from inside the door?

Xiaoman's hand had already reached for the keyboard, but she abruptly stopped.

Xu Wangshu pressed her hand down, her voice low: "It's asking about the inside of the door, but we don't know which side it's on."

Wen Zhaolin looked at the words through the glass and suddenly smiled. There was no pride in that smile, only weariness.

"The first encounter always starts with a seemingly harmless question."

Qin Lan had someone take notes, but didn't respond. Just as the notes were being written, an inverted repair number slowly emerged from the dust on the back of the old radio.

XJ-0717.

At the same time, Zhou Jianguo's field terminal suddenly connected to the main control room. In the video, Old Zhou was squatting next to a manhole cover, while Chen Rui held a flashlight, his face pale.

The manhole cover was closed.

But from under the manhole cover, came three short and two long knocking sounds.

Qin Lan then disassembled the old radio, but didn't let anyone take it away. She ordered someone to find a transparent evidence box, sealed the radio along with the cut power cord inside, and affixed three seals from different departments. As soon as the seals were pressed in, the radio made a soft sound again.

It's not about knocking.

It's like someone is breathing inside a box.

"Record it," Xu Wangshu said.

The technician's pen trembled slightly: "Record what?"

"It was recorded that it continued to attempt to produce vital signs even after being sealed away."

This statement caused the young researchers' expressions to change. The phrase "vital signs" carried immense weight; once written down, many procedures would automatically shift towards rescue, protection, ethical review, and even suspension of quarantine. Xu Wangshu, however, added: "The source of these characteristics has not been verified and does not constitute a determination of life."

Wen Zhaolin looked at her and suddenly said, "You're more ruthless than we were back then."

"No." Xu Wangshu didn't look up. "Back then, you were afraid of missing out on life, so you opened the door. Now I'm also afraid of missing out on life, so I won't let a fake life drag a real person in."

Outside the main control room, the first batch of public reports flooded in. Some said their old tape recorders were playing, others said the parking lot gates were emitting the voices of loved ones, and still others filmed motion-sensor lights in their apartment building flashing three short and two long. Qin Lan neither concealed anything nor created panic. She had the official notice written in an extremely simple style: If you encounter any unusual sounds, do not approach, do not respond, do not answer on behalf of others, record the location, and wait for verification.

A sentence slowly appeared on Lin Jibai's screen.

[It's written like a property management notice, which is good.]

Xiaoman sniffed: "You're already like this and you still complain about the writing style?"

The more it resembles property management, the less it resembles a divine oracle.

Looking at this sentence, Xu Wangshu suddenly understood what Lin Jibai was trying to defend. He wasn't just being sarcastic; he was using the most ordinary tone to pull everyone back from their mythical fear. As long as they would still complain about the property management notices, they wouldn't easily kneel before the voices outside the door.

After this property management notice was sent out, the first to report it wasn't to the space center, but to the guardhouse of an old residential complex. The old man on night duty said that the radio in the guard booth at the gate was also playing. He originally wanted to yell at whoever was causing trouble in the middle of the night, but remembering the notice, he swallowed his words, took a picture, and unplugged the socket.

When the photo was transmitted to the main control room, Xu Wangshu stared at it for a long time. Next to the radio hung a bunch of keys, with the building number written on the key tags. If someone were to answer "yes" for that knocking, it might not need to decipher any advanced permissions; it could simply follow these common access points to find the doors to the entire building.

Qin Lan immediately added a second point: If there are keys, access control devices, medical records, or employee badges near the abnormal equipment, objects that could point to a specific person or space should be isolated first. Do not move the source of the abnormality, and do not approach it in order to get a clearer shot.

Lu Chenggong looked at the supplementary statement and said in a low voice, "It didn't come down from the sky; it found a crack in our hands."

Wen Zhaolin nodded, his face grim: "The old system was best at calling seams 'interfaces'."

The radio in the evidence box suddenly exhaled again, and a thin layer of fog covered the box walls. The fog didn't dissipate, but instead condensed into half a fingerprint on the transparent plastic, as if an invisible hand had pressed it from the inside.

Xiaoman hugged the toolbox tightly: "It's testing who will have a soft spot."

Xu Wangshu photographed and filed the fingerprint, her voice calm: "Then let it know. It's okay to be soft-hearted and write a record first."