She had been listening for thirty-one days. The signal had not wavered, not paused, not changed. It pulsed its primes into the void with the patience of stone, and Kael sat in the ruins catching them like a woman cupping water from a river that would never stop flowing.
Thirty-one days of primes. She knew the sequence better than her own heartbeat. She dreamed in numbers now — 2, 3, 5, 7, a rhythm that underlay her sleep like the pulse of the ocean against the harbor wall.
It was time to stop listening.
She went to Sekani first, because Sekani would give her the reason she wanted to hear. She found him at the north gate, wrapped in his blanket despite the afternoon heat, his milky eyes tracking the road with a precision that suggested he was seeing something other than what was in front of him.
"The listening machine," she said. "You were right. It works."
Sekani's hands stilled on his blanket. "What did you hear?"
"Numbers. Coming from the south. A mathematical sequence that no natural process can generate."
He was silent for a long time. Then: "The sky-voices."
"I don't know what they are. I know they're real. I know they're intelligent. And I know they've been transmitting for a very long time."
"Are you going to answer?"
"I'm thinking about it."
Sekani nodded. His expression — if the wrinkles and the sun damage and the eighty years could be called an expression — was neither surprise nor excitement. It was something closer to grief. "My mother told me about the sky-voices. Her mother told her. The story goes back as far as anyone remembers. We knew they were there, Kael. We just couldn't hear them." He paused. "If you answer, everything changes."
"I know."
"Answer anyway."
She went to Renna next, because Renna would give her the reason she didn't want to hear. Renna was in the trade hall, negotiating a dispute between two harbor merchants with the brisk efficiency of a woman who understood that most problems were really the same problem wearing different clothes. She was forty-five, sharp-jawed, sharp-tongued, and she had never met a situation she couldn't turn into leverage.
"A signal from the south," Renna said when Kael finished explaining. "Intelligent. Technological. And you want to respond."
"I want to know if someone's alive."
"So do I. But what I really want to know is: if someone is alive down there, what do they have that we want?"
"That's not why—"
"Everything is trade, Kael. Even conversation. You offer words; you receive words. The question is always: what is each side getting?" Renna leaned back. "Answer them. If they're real, we need to be the city-state that made first contact. If they're not real, we lose nothing but the power to run your transmitter."
The reason Kael didn't want to hear, and the reason she needed: this was not just science. This was politics, trade, power. The signal would change the world, and the world would not change gently.
She went to the observatory that night.
Building a receiver had been an act of restoration — the equipment existed, they just had to make it work. Building a transmitter was an act of invention. Nothing in the sealed room was designed to send. It was all ears, no mouth.
Kael and Olu spent three days improvising. The principle was sound — reverse the signal path. Instead of collecting electromagnetic energy from the dish and converting it to information, convert information into electromagnetic energy and radiate it from the dish. The power requirements were substantial. Their salvaged battery array wouldn't cut it; they needed a sustained power source.
Demi solved this with the blunt practicality that made her invaluable: she ran a cable from the city's nearest generator — a water-wheel-powered dynamo on the river a kilometer north — to the observatory, working through two nights to lay and splice the line. The generator's owner was told it was for a new workshop. It was not entirely a lie.
The transmitter itself was crude. Olu built an oscillator from components scavenged from the receiver's spare parts — replacing what he'd taken with even cruder workarounds so the receiver would still function. Kael fashioned the modulation circuit, using her glass-grinding precision to solder connections that needed to be exact or the frequency would drift. The dish could serve as both receiver and transmitter, but not simultaneously — they would need to switch between modes, which meant they could only send or listen, never both at once.
On the fourteenth night of the second month, they were ready. The transmitter hummed with the particular vibration of a machine that had been built from desperation and might work, or might not, but was the best they could do.
Kael sat before it with her hand on the modulation key — a simple switch that Demi had machined from brass — and felt the weight of what she was about to do. For five hundred years, no one on this side of the ocean had spoken to whatever was on the other side. The silence had become the shape of the world. She was about to change the shape.
She transmitted at midnight, when the ionosphere was quietest and VLF propagation was strongest.
Her message was simple: the same prime sequence she had been receiving, transmitted back. 2, 3, 5, 7, 11, 13, 17, 19, 23. A mirror. A proof that she had heard and understood. Each number was encoded as a series of pulses — two pulses for 2, three for 3, five for 5 — crude but unambiguous. She sent the sequence three times, spaced five minutes apart, then switched the dish back to receive mode.
And waited.
The VLF propagation time for a signal to travel from the Caribbean to the southern hemisphere through the Earth-ionosphere waveguide was approximately eight to twelve minutes, depending on ionospheric conditions. She knew this from Olu's calculations. She also knew that even if someone received her signal, they would need time to process it, decide to respond, compose a response, and transmit.
She expected to wait hours. Maybe days. Maybe forever.
The response came in fourteen minutes.
It arrived as a burst of modulation on the VLF frequency, slightly offset from the original signal — as if the sender had shifted to avoid interference with their own probe. The encoding was different from hers: cleaner, more efficient, with error-correction patterns she didn't recognize. But the content was unmistakable.
1, 1, 2, 3, 5, 8, 13.
Fibonacci numbers.
Kael stared at the receiver. Her hands were shaking. Olu, beside her, was saying something she couldn't hear because the blood in her ears was louder than his voice. Demi stood in the doorway with her mouth open.
They had sent primes. She had sent primes back. And someone — not a machine cycling through old recordings, not an echo, not an atmospheric trick — someone had received her primes, understood them, and responded with a different mathematical sequence of equal significance.
She had said: I hear you. I understand.
They had said: We hear you too. And we understand something different.
The Fibonacci response was not a mirror. It was a conversation. It said: I received your primes, and here is my offering — a sequence you did not send, that proves I am thinking independently, that proves I am not an echo of you.
She was talking to someone.
Kael pressed the modulation key again. Her hands were still shaking but her mind was glass-clear now, clear as the finest lens she'd ever ground, everything sharp and true. She transmitted: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Cardinal numbers. Counting. The next logical step — if you understand primes and Fibonacci, let us establish that we both count the same way.
Seven minutes passed. The response: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 — repeated exactly. Confirmation. Then, appended: 10+1=11. Basic arithmetic. An invitation to the next level.
They were building a language.
Kael and the unknown intelligence exchanged mathematics until dawn. By the time the eastern sky began to lighten, they had established: counting, addition, subtraction, multiplication. The entity on the other end learned as fast as she proposed new concepts — faster, in fact. Where Kael needed multiple examples to verify mutual understanding, the entity grasped the pattern from a single instance and extrapolated correctly. This was either the work of a brilliant mind or a system designed for pattern recognition, and Kael could not tell which.
When she finally stopped transmitting — hands cramped, eyes raw, body vibrating with exhaustion and something that felt like reverence — the VLF channel went quiet for several minutes. Then the probe signal resumed: 2, 3, 5, 7, 11, 13, 17, 19, 23. The same pulse that had been running for what she now knew was years. Decades. Maybe centuries. The entity had spoken to her for hours and then returned to its vigil, its beacon, its patient call into the void.
Kael sat on the concrete floor of the sealed room. Olu was asleep in a corner, his head on his arms. Demi had gone outside to pace, which was how Demi processed anything that exceeded her considerable tolerance for the unusual.
Kael was alone with the receiver and the fact that the world had changed.
She was not alone. Humanity was not alone. Whoever — whatever — was on the other end of that signal was intelligent, technological, patient, and willing to talk. They had been calling for a very long time, and someone had finally picked up.
The tears came without warning. Kael did not cry often and did not cry easily and she was not, in her own estimation, a person for whom emotion preceded thought. But she sat on the floor in the ruins of a civilization's last great ear and she wept, and the weeping was not sadness. It was the overwhelming pressure of a truth too large for her body to hold: five hundred years of silence, broken. By her. In the dark. With a machine she barely understood and a language she was inventing on the fly.
She wiped her face with the back of her hand and tasted salt. She thought about Sekani's story: a listening machine, because the act of listening was its own kind of faith. She had listened. She had been heard. And now she needed to do the hardest thing she would ever do, harder than decoding the signal, harder than building the transmitter, harder than believing the impossible.
She needed to tell people.
Because this was not hers. This discovery, this signal, this conversation with the bottom of the world — it belonged to everyone. And everyone would want a piece of it, and everyone would fight about what it meant, and the politics would be ugly and the arguments would be loud and the simple, staggering beauty of two intelligences finding each other across an impossible ocean would be ground down into factions and strategies and competing claims.
But that was what it meant to be human. You found something miraculous, and then you fought about it, and then — if you were lucky — you figured out what to do with it together. The fighting was the point. The fighting was how you learned what the miracle meant.
Kael stood. Her legs were stiff, her back ached, her eyes burned. Dawn light came through the cracks in the ceiling, catching the dust in the air, turning it to gold.
She would tell them. Tomorrow. Today she would sleep, and in her sleep she would dream of numbers — not primes this time, but a new sequence, given by a stranger in the dark, a gift of intelligence from the other side of the world.
1, 1, 2, 3, 5, 8, 13.
The Fibonacci sequence. Each number the sum of the two before it. A pattern that built itself from its own history. A sequence that could only go forward by remembering where it had been.
It was, she thought, a very good way to begin.