She told two people. This was either the smartest or the stupidest thing she'd done since the day she burned her arm.
Demi was a metalworker's apprentice with steady hands and no imagination, which was exactly what Kael needed — someone who would do what was asked without asking why. Olu was a scholar-house archivist who had once spent three years reconstructing a pre-Sundering water pump from fragments and a diagram so faded it looked like a ghost of engineering. He had the patience of stone and the curiosity of a child and he owed Kael four lenses.
She brought them to the sealed room on the eighth night and showed them what she'd found.
Olu touched the receiver assembly with fingers that trembled. "Do you know what this is?"
"I know what it does. It listens."
"It does more than listen." He traced a cable up the wall. "This is connected to the dish above. The dish collects energy from a specific frequency range — radio waves, if the old texts are right. This—" He placed his palm on the receiver. "This converts that energy into information. Sound. Data. Whatever was being transmitted on that frequency."
"Transmitted by whom?"
"That's the question, isn't it?"
They spent two weeks on their hands and knees in the sealed chamber, mapping connections, cleaning corrosion, tracing cable runs. Demi reinforced the structural supports where the ceiling had cracked. Olu deciphered labels — symbols in Technical Latin that, with agonizing slowness, yielded their meanings: FREQUENCY. GAIN. AMPLITUDE. AZIMUTH. Words that described a machine built to do one thing with extraordinary precision: detect signals from far away.
The dish itself was partially collapsed, but the central section — perhaps forty paces across — remained intact. Its surface was pitted and corroded, but the parabolic curve was still true. It had been engineered to survive. Kael wondered about the people who built it: what kind of faith must they have had, to pour this much precision into a machine for hearing things that might never speak?
She thought about Sekani's story. A listening machine. An ear pointed at the sky. She had dismissed it as mythology. It was not mythology. It was engineering so audacious it had become indistinguishable from prayer.
By the fourteenth day, they had the receiver powered — a crude arrangement of salvaged batteries from the city's electrical stores, connected through cables that Kael had spliced with the same precision she used for her finest lenses. Olu had identified the tuning mechanism: a series of dials, corroded but functional, that adjusted the frequency range the receiver monitored. The labels were still readable: numbers in a notation system that mapped to frequencies of electromagnetic radiation.
Kael set the dials to the lowest frequency she could and listened through a crude earpiece they'd fashioned from copper wire and a ceramic disk. Static. White noise. The voice of the universe talking to itself — random, patternless, the electromagnetic equivalent of wind.
She moved the dials. More static. Different textures of nothing.
She did this for three nights.
On the seventeenth night, she found something that wasn't nothing.
It came in on a frequency lower than she'd expected — below the range the old labels indicated, down in the band that Olu's texts called VLF, very low frequency. She almost skipped past it. The signal was faint, buried in noise, a whisper beneath a shout. But Kael ground lenses for a living. Her entire skill was the detection of imperfections in what appeared smooth — the hair-thin ridge, the microscopic flaw, the deviation from true. She heard the signal the way she felt a bad curve in glass: not with her ears but with some deeper faculty, the part of the brain that recognizes pattern before the conscious mind has finished asking the question.
A pulse. Regular. Repeating every 4.7 seconds.
She held her breath. Counted. One-two-three-four — pulse. One-two-three-four — pulse. One-two-three-four — pulse.
It could be natural. Lightning, maybe. Some atmospheric phenomenon she didn't know about. But natural signals didn't repeat at exactly the same interval. Natural signals drifted, stuttered, varied. This was precise. This was a metronome.
She adjusted the dish's orientation. The signal strengthened when she tilted south. It weakened when she moved north, east, west. South. The signal came from the south.
South was ocean. South was the Crossing — the mythic barrier, the graveyard of ships, the end of the world. South was nothing. No one lived south. No one could live south.
The pulse continued. One-two-three-four — pulse. One-two-three-four — pulse. Patient. Steady. As if it had been doing this for a very long time and was prepared to continue for a very long time more.
Kael stopped sleeping normally. She ground lenses by day — she still needed to eat — and spent every night at the observatory, mapping the signal. She brought paper and ink and recorded every pulse, marking the intervals, the duration, the subtle variations in strength that correlated with time of day. The signal was not constant; it fluctuated in a daily rhythm that she eventually recognized as ionospheric variation — the signal propagated better at night when the upper atmosphere cooled and settled. This told her two things: the signal traveled through the ionosphere, not through the ground, and it traveled a very long distance.
By the twentieth day, she had enough data to attempt something more sophisticated. She began looking not just at the pulse timing but at the pulse structure. The signal wasn't a simple on-off beep. It was modulated — the pulse contained information, a pattern within the pattern. She spent two sleepless nights decoding it and then sat back on the concrete floor and stared at the ceiling and felt the world shift under her like the deck of a ship.
The pattern was mathematical.
Not random. Not atmospheric. Mathematical. Groups of pulses in sequences that resolved, with sickening clarity, into numbers. She checked three times. She checked a fourth. The sequence repeated on a cycle: 2 — 3 — 5 — 7 — 11 — 13 — 17 — 19 — 23 — then repeat.
Prime numbers.
Kael knew prime numbers. Every glass-eye did — they were fundamental to the mathematical training that underpinned the scholarly tradition. Numbers divisible only by one and themselves. The building blocks of arithmetic. Universal. Irreducible.
And significant, because no natural process generated sequences of primes. Lightning didn't count in primes. Atmospheric noise didn't sort itself into the fundamental sequence of number theory. Stars didn't pulse in patterns that mapped to mathematical constants.
Only minds did that.
Someone — something — was transmitting a sequence of prime numbers from the south, through the ionosphere, at a frequency that required massive antenna infrastructure to generate, on a signal that had been running long enough to develop the patience of geology. And Kael was the only person in the world who was listening.
She told Olu and Demi. Olu went pale. Demi asked if it could be a malfunction in the equipment. Kael said no — the signal was external, consistent, and pointed. The equipment wasn't generating it; the equipment was receiving it.
"Who?" Olu said.
"I don't know."
"What do we do?"
Kael sat in the sealed room, the receiver humming its quiet catch of impossible numbers, and thought about the weight of what she held. If she was right — and she was right, she had checked, she had checked again, the primes were there — then this was the most important discovery in five hundred years. Someone was out there. Someone with technology, with mathematics, with the will to send a signal into the void and wait for an answer. Someone who had been waiting longer than the oldest person in Tidemouth had been alive.
She thought about telling the scholarly council. She thought about the politics that would follow — the factions, the arguments, the people who would claim it and the people who would deny it and the people who would try to use it. She thought about the merchant captain who wanted his spyglass. She thought about Moss on the dock, bent over a hull, the only person she knew who had ever sailed south and come back.
She thought about the signal, pulsing in the dark. 2, 3, 5, 7, 11. The language of mathematics, spoken by someone she had never met, directed at no one in particular, or perhaps directed at anyone with the ears to hear it.
Not yet. She wouldn't tell anyone else yet. Not because she was afraid — she was afraid, but that wasn't the reason. She wouldn't tell them yet because she needed to know one more thing first. She needed to know if the signal was a recording, a relic, a ghost of old technology cycling mindlessly through a dead program — or if someone on the other end was alive.
There was one way to find out. You could listen all you wanted, but listening only proved the signal existed. To prove someone was alive, you had to do something more dangerous than listening.
You had to answer.
Kael sat in the ruins of a dead civilization's greatest ear, surrounded by the hum of a five-hundred-year-old signal from the bottom of the world, and began to think about how to build a transmitter.