The Mississippi didn't run so much as it lay, thick and brown and slow, like a sleeping animal that might wake at any moment. Ellis McCullough knew this the way he knew the back of his own hands. He had been fishing these banks since he was old enough to hold a rod, and he knew which bends held catfish and which stretches were deep enough to drown a man.

He was thirteen, thin as a reed and just as flexible, with skin already weathered by the sun and the damp that seeped into everything in this part of Louisiana. His mother Ruth worked for the plantation owner's wife, scrubbing linens until her hands were raw and cracked. They lived in a cabin that leaned to one side like a tired man leaning against a wall, and the roof leaked when it rained hard.

The pearl was sitting in the mud at the edge of a backwater, half-buried and glowing with a faint blue light that made Ellis stop and stare. It was the size of a hen's egg, smooth as glass, and when he picked it up, it was warm. Not sun-warm. Something else. Something alive.

He turned it over in his hands. The mud of the riverbank was dark and rich, and the pearl seemed to drink the darkness and throw it back as light. Ellis had never seen anything like it. He'd heard stories, of course. Old folks sitting on porches in the evenings, talking about things in the river that weren't quite fish and weren't quite anything else. Things that glowed. Things that called to people in their sleep.

He put the pearl in his pocket and went home.

That night, he dreamed of the river. Not the slow, brown river he knew, but a river of light, wide and luminous and alive, and in it something vast was moving. Something old. It spoke to him in a language he didn't understand but somehow knew, and it told him to come back. To bring the pearl back to the water.

He woke with the pearl burning against his thigh and a thirst so fierce he had to drink from the bucket by the bed. The water tasted wrong. Everything tasted wrong now. Like ash. Like the river.

In the days that followed, Ellis noticed changes. His skin was darker, but not from the sun. Dark blue patterns were spreading across his arms, faint as shadows, shaped like scales. His eyes felt different too—sharper, able to see in the dim light of the cabin when before he'd needed a candle. And the water. God, the water. He found himself standing at the riverbank for hours, staring at the surface, feeling the pearl pulse against his hip like a second heartbeat.

Ruth noticed. She was a lean, hard woman who had survived a difficult birth and a harder life, and she noticed everything.

"Ellis," she said one evening, grabbing his arm. "What's happening to you?"

"Nothing, Ma," he said, and pulled away. But his arm was wrong. The blue patterns were visible now, even in daylight, and they were spreading.

Ruth's face went pale. "You need to put it back," she whispered. "Whatever you found, you need to put it back in the river."

"I can't," Ellis said. "If I lose it, they'll come."

He meant the McCullochs. Not his family—the other McCullochs, the ones who owned the plantation up the river. Silas McCullough was a fat man with cold eyes and a reputation for taking what he wanted. He had noticed that Ellis's mother was no longer begging at the kitchen door. He had noticed that they were eating meat instead of cornbread and water. And Silas McCullough did not like things he could not control.

His men came on a Saturday afternoon, when the heat was thick enough to chew. Three of them, on horseback, dust rising behind them like smoke. Silas rode at their head, his face red and shiny in the sun, his eyes fixed on Ellis with the single-minded focus of a man who had never been told no.

"Boy," Silas said, dismounting with the practiced ease of a man who owned everything he touched. "I hear you've been sitting on something that doesn't belong to you."

"I don't know what you mean," Ellis said. He was standing in the doorway of the cabin, one hand in his pocket, the pearl burning against his palm.

Silas smiled. It was not a nice smile. It was the smile of a man who had just found something he wanted and knew he could take it. "Don't play dumb with me, boy. I know about the pearl. I know what it is. And I know you don't have the right to keep it."

Ruth came out of the cabin, wiping her hands on her apron. "Leave him alone, Silas. He's just a boy."

Silas turned to her, and his eyes were like flint. "Just a boy who has something that belongs to me. Now, where is it?"

Ellis felt the pearl in his pocket, pulsing faster, faster, like a bird trying to escape. He thought of Ruth, standing there in her worn dress, her hands cracked and red. He thought of the river, calling to him in his dreams. He thought of the blue patterns on his arms, spreading, changing him.

He took the pearl out and swallowed it.

It went down like swallowing a live coal. Fire exploded in his chest. He doubled over, gasping, as something shifted beneath his skin, something vast and ancient and hungry waking up inside him. His skin darkened to a deep, iridescent blue. His eyes burned with a light that made Ruth scream.

"Ellis," she whispered. "My boy—"

He could not speak. His throat felt wrong, constricted, as if something were growing inside it. He turned and ran toward the river, and Ruth ran after him, calling his name, but he did not stop.

He reached the bank and didn't hesitate. He ran into the water, and it took him in like an embrace, thick and warm and alive. He sank beneath the surface and did not drown. He breathed water the way a fish breathes it, and the thing inside him—the pearl, the power, the curse—unfurled like a flower in the dark.

Behind him, the river carved channels into the bank. One channel. Two. Seventeen channels in all, each one a testament to the place where he had paused, where he had turned his face toward the cabin one more time, where he had wept tears that carved deep into the earth.

Silas and his men arrived at the riverbank too late. Something large and dark had slipped beneath the surface, something that moved through the water with a power no creature should possess.

Ruth lived another thirty years. Every morning, she walked to the river and stood at the edge and watched the water. Every evening, she returned home and placed seventeen stones on the porch step, one for each channel, one for each time her son had looked back. She never spoke of what happened to her boy. She did not need to. The river told the story for her, in the language of water and mud and silence.

And on certain evenings, when the heat was thick and the cicadas screamed and the Mississippi lay still as glass, the people up and down the river swore they could see something moving beneath the surface. Something large. Something that remembered.