I

The fog came in off the Thames like a living thing, thick and yellow and smelling of coal smoke and river rot. Evelyn Cross stood at the telescope in the Hampstead observatory, her breath fogging the brass fittings, and watched the stars perform a trick they had never performed before.

They were wrong. Not wrong in the way astronomers sometimes are when they miscalculate a trajectory or misread a spectrograph. Wrong in a deeper sense. The stars were flattening.

It began as a subtle distortion in their light, a stretching of their luminance into thin colored lines that seemed to reach across the sky like fingers. Evelyn had been tracking the anomalous signal from the binary system for eleven months, and she understood now what it meant. The geometry was propagating. A wave of dimensional decay was moving through space, and it had reached the edge of the solar system.

She wrote the equations on the glass of the observatory window with her gloved finger. Three dimensions becoming two. Space itself losing its depth. The mathematics were beautiful and terrible, and they described the end of everything.

II

They called her mad within a fortnight.

When she presented her findings to the Royal Astronomical Society, the senior fellows listened with polite incomprehension, then exchanged glances that said what they would not say to her face: a woman playing at mathematics, a spinster with a telescope and delusions of grandeur.

"The signal describes a geometric transformation," she told them, her voice shaking but clear. "Space in that region is collapsing from three dimensions to two. If this propagation continues—and all evidence suggests it will—it will reach our solar system within approximately eighteen months."

Lady Margaret Ashby, her cousin once removed and the architect of her current misery, had arranged for her attendance at the meeting. Margaret sat in the front row in a dress of severe black lace, her expression one of practiced concern that couldn't quite hide the satisfaction beneath it.

After the meeting, as Evelyn gathered her notes, a distinguished astronomer named Pemberton approached her with the condescension reserved for children and lunatics.

"My dear Miss Cross," he said, "I appreciate that imagination is a valuable quality. But mathematics is not the domain of—well. Of everyone. Perhaps you would find greater satisfaction in embroidery?"

The word mad followed her home like a shadow. It followed her into the house where Lady Margaret had installed her, under the pretext of providing a suitable environment for her "nervous condition." It followed her into the garden where she would sit for hours, staring at the fog-shrouded hills, watching for the first signs of the flattening.

Dr. Alistair Blackwood arrived three days later with a leather case and a manner that suggested he was administering a divine favor rather than committing a woman to an institution.

"Dimensional decay," he repeated, writing on his pad. "You believe the universe is becoming flat."

"I have calculated the propagation rate. The mathematics are clear."

"Mathematics," he said, making another note. "Yes. The mad are always so confident in their mathematics. Have you ever considered, Miss Cross, that the mind can construct its own geometries? That the brain, under stress or imbalance, might produce elaborate mathematical fantasies?"

Evelyn looked at him with the flat eyes of someone who has already heard this sermon. "You are going to lock me up."

"I am going to help you," he said, and the certainty in his voice was worse than any threat.

The treatment began that evening. Cold baths that stole her breath. Electrical apparatus that made her teeth vibrate for hours. Blackwood standing over her with a calm pastoral face, delivering sermons about the corruption of her mind and the salvation to be found in surrender.

But in the nights, when the institution was quiet and the other patients lay sleeping in their iron-framed beds, Evelyn scratched equations into the stone wall behind her bed. She scratched them with a piece of wire she had concealed in her sleeve, scratching them over and over until the stone wore shallow and the wire bent. The equations were her prayer. The equations were her proof that she was sane. The equations were the only thing that kept the fog from entering her mouth while she slept.

III

She escaped on a Tuesday in November, through a window whose bars had been loosened by years of London frost and her own patient picking with the bent wire. She ran through streets that smelled of coal smoke and horse manure, wearing a borrowed shawl and a man's hat, her scientific instruments wrapped in oilcloth beneath her arm.

The signal had changed. It was no longer a periodic pulse from the binary system. It was a continuous broadcast, and it carried images now. Evelyn decoded them in a lodging house in Whitechapel by the light of a tallow candle, her hands shaking not from fear but from the terrible beauty of what she saw.

A city. A vast city of spires and domes and crystalline structures, and then—flattening. Not destruction. Transformation. The buildings became two-dimensional images of themselves, precise and beautiful as engravings, and the people within them became part of the images, their faces caught in expressions of surprise and wonder and something like acceptance. The civilization of the Zephyrians was being painted into existence, and in being painted, was ceasing to exist.

Evelyn wept. She wept for them and she wept for London and she wept for the telescope in the Hampstead observatory that no one would ever use again.

She tried to reach the government. She tried to reach anyone who might listen. But the world had other concerns in 1888, and a madwoman running through the streets with equations scrawled on her skin was not one of them.

She stood on the bank of the Thames at dawn on a morning she would never forget, and she watched the Moon begin to flatten.

It happened slowly at first—a stretching of its luminance, a darkening along one axis, as if an invisible hand were pressing against it. Then faster. The craters became lines. The maria became washes of color. The Moon became a disc, then an ellipse, then a thin bright line, and then—a sheet. A perfect two-dimensional circle of silver light hanging in the sky, no thicker than paper, reflecting sunlight from a surface that had no depth.

Evelyn reached up with her gloved hand. The lace of her glove passed through the two-dimensional Moon without resistance, as if touching a photograph of the Moon rather than the Moon itself. And yet the light was real. The warmth was real. The terrible beauty was real.

IV

The solar system became a painting. Every planet, every asteroid, every speck of dust was pressed into the great two-dimensional canvas that had once been three-dimensional space. The Earth became a blue and green disc, beautiful beyond words, and then it was gone.

Evelyn remained. She does not know why. Perhaps the years of treatment in Blackwood's institution had altered her mind in some unexpected way, given it a resistance to dimensional collapse. Perhaps the equations she had scratched into the stone wall had changed something fundamental about her consciousness. Perhaps it was simply that she had been prepared for this by a lifetime of being treated as if she already existed in two dimensions—flat, reduced, invisible.

She carries five kilograms of three-dimensional matter. A stack of star charts from the Hampstead observatory. The decoded records of the Zephyrian signal, written in her precise handwriting on paper that is impossibly thick in a thin world. And a rose from the observatory garden, pressed between two sheets of glass, its petals impossibly three-dimensional in a universe that has forgotten depth.

She drifts. There is no up or down in a two-dimensional universe, only directions along the great flat plane that was once space. She drifts through what were once cities and now are paintings of cities, through what were once forests and now are paintings of forests, through the infinite gallery of a universe that has become its own monument.

The rose petals unfold in her hands, and each petal is a world. Each world is flat and perfect and eternal. And Evelyn Cross, the woman who was called mad, floats through the dimension elegy, carrying the memory of depth in a depthless world, the last three-dimensional consciousness in a two-dimensional eternity.

She does not die. She cannot die. Death would be a mercy, and mercy is not part of this mathematics.

She simply floats, and remembers, and is forever alone.