At 09:17 Universal Time, the sunlight vanished from the windows of the Asterion Observatory. It did not dim. There was no long twilight, no amber warning at the edges of the horizon. One moment, Dr. Iona Vale was watching dust turn in a square of gold above her desk. The next, the square was gone.
Her coffee cup rattled against the saucer when the building's emergency shutters closed. In the corridor, someone cried out. The observatory's automated voice said, with the extraordinary calm reserved for disasters, "External illumination anomaly. Remain in your assigned section."
Iona looked at her watch. It had been eight minutes and nineteen seconds since the solar monitors recorded a disturbance at the Sun's surface. That was almost exactly the travel time of light from the Sun to Earth. No machine on the planet could have changed that number, which was what frightened her most.
She called up the solar feed. The image was a flat circle of black, so perfectly defined that it looked pasted over the instruments. Around it, the distant stars remained sharp. The Sun had not exploded. Its gravitational field was steady. The planets were still following their orbits. The neutrino counters continued to tick.
Only the light was missing.
"Say that again," said Tomas through her earpiece.
Her younger brother worked at the municipal heat exchange beneath the city. He had called as soon as the streetlights came on in daylight. Somewhere behind him, pumps hammered in uneven rhythm.
"The Sun is still there," Iona said. "We just can't see what it's sending us."
"That is not a reassuring distinction."
"It's the only honest one."
Outside, the city of Selene Bay spread along a northern coast that should have glittered beneath a thin autumn sun. Its seawall lamps now traced pale lines across the harbor. Cars sat motionless at intersections while drivers leaned from their windows to stare upward. Above them was a sky full of stars, too many stars for the hour, with one impossible absence at its heart.
The observatory director entered without knocking. Director Sato was a precise woman who had spent three decades avoiding dramatic statements. Now she carried a tablet in both hands as if afraid it might fall.
"Every solar telescope is reporting the same," Sato said. "Lunar stations too. Orbital arrays. Nothing from the Sun in the optical band. Almost nothing in infrared."
"How long until we know the cause?"
Sato held out the tablet. "We received this on the emergency science channel. It was sent at 09:08, before the light went out here."
The message contained eleven words, repeated seven times in a simple text packet. It had originated from a maintenance transmitter beyond the Moon. The sender identification belonged to a facility decommissioned fifty-two years earlier.
KEEP THE SKY CLOSED. DO NOT TRY TO BRING BACK DAYLIGHT.
Iona read it once. Then a second time.
"A prank?" she asked.
"The authentication key is valid."
"Keys can be stolen."
"This one has never been used outside the Archive."
Iona felt a strange pressure behind her eyes. On her childhood wall had hung a photograph of her mother, standing in the wheat fields under an ordinary, unremarkable blue sky. Her mother had once said the Sun was the only clock the whole planet shared. Iona had not understood how comforting that was until the clock stopped.
She enlarged the authentication data. The old transmitter was called the Lantern Gate. Its final recorded mission had been classified under a program with an innocuous name: Atmospheric Reflection Study.
Iona knew the program. Her doctoral supervisor had warned her never to waste time researching it. Supposedly, it had been an abandoned experiment in solar radiation management. Supposedly, its records had been destroyed.
Yet the message was real. The transmitter was active. And somehow, someone at the Lantern Gate had known what would happen before the darkness arrived.
"Get me a secure link to the Archive," Iona said.
Director Sato did not move. "There is another problem."
A second pane appeared on the tablet. It showed Earth from an orbital weather satellite. Across the planet, the darkness lay like a stain. In the upper atmosphere, thin silver threads flashed and vanished. They formed a geometric pattern, too regular for an aurora.
"What am I looking at?" Iona asked.
"We were hoping you could tell us."
The silver lines appeared again. This time they curved toward each other, making a vast, incomplete ring around the dark side of the world.
Iona thought of the warning on the tablet. Keep the sky closed.
Whatever had happened to the Sun, someone had built a door between it and Earth. And the door was still moving.