The desert doesn't care if you live or die. It's not cruel. It's not kind. It just is.

Bill Harlan knew this the way he knew his own name. Six years of walking the Colorado Territory had taught him everything he needed to know about survival, and the first lesson was always the same: the land would not help you. Nobody would help you. You were on your own.

Except he wasn't entirely on his own. The thing in his blood had other ideas.

It had started in the war. A skirmish near the San Juan Mountains, six years ago. His squad—eight men, including Bill—had been ambushed by a combined force of Ute warriors and what looked like regular soldiers wearing the wrong uniforms. Bill had survived because something in his body had changed. Something had woken up. He had moved faster than he ever had in his life. He had taken bullets that should have killed him and kept running. He had fought off three men with his bare hands.

Afterward, the doctor said he was lucky. The other seven men in his squad said he was a monster. Bill didn't know what to think.

He knew one thing: the thing inside him was eating him alive.

His liver hurt all the time. His vision blurred at the edges. He had nightmares about water—dark, still water in underground pools, and something moving beneath the surface. Doc Sullivan said it was the parasite. Bill didn't know what else to call it. A worm, Doc had said, after looking at a slide of Bill's blood under his microscope. A species we've never seen before. It lives in your nervous system. It's controlling your adrenal glands. Making you stronger. Making you faster. Killing you slowly.

"How long?" Bill had asked.

Doc had shrugged. "Years, maybe. Months, maybe. Depends on how much you use it. Every time your body goes into that... fight mode... it accelerates the damage."

Bill had paid Doc in whiskey and walked away.

Now they were walking again. Not together—Bill and Doc had been traveling together for three years, but today they were parting. Doc was heading south to Denver, where he'd heard rumors of a medical school that might take him despite his controversial theories. Bill was heading north, toward the San Juan Mountains, toward the place where it had all started.

"You don't have to go back," Doc said, leaning on his cane at the crossroads.

"I know," Bill said.

"If whatever's inside you is going to kill you, why go back to where it started?"

Bill looked at the road. It stretched north through flat desert, past rocky hills, toward the mountains that had been his home before the war. Before the ambush. Before the thing in his blood made him something he didn't understand.

"Because I need to know why," he said.

Doc nodded. He didn't argue. He never did. He just handed Bill a small cloth bundle. "More of the suppressant. It'll buy you another month, maybe two. Don't push yourself."

"I never do," Bill said.

Doc smiled—a crooked, tired smile. "That's what I'm afraid of."

They parted at noon. Bill walked north alone. The sun beat down on the desert like a hammer. He didn't feel the heat the way other men did. The parasite changed that too—his body temperature ran higher, his sweat glands were more efficient. He could go longer without water. He could walk farther. He could carry more.

All of it was killing him.

By the third day, he reached the San Juan Mountains. The ambush had happened in a narrow valley between two peaks. Bill remembered the sound of the rifles, the smell of gunpowder, the feeling of the parasite flooding his blood like liquid fire. He remembered killing men—men he couldn't see coming, men whose movements he had predicted before they moved. He had been a different person in that valley. Something not entirely human.

He found the valley easily. It was the same as he remembered: narrow, steep-sided, with a dry creek running through the bottom. And on the far side of the valley, half-hidden by rocks and brush, he saw something that made his breath catch.

A cave.

Not a natural cave. A cave that had been opened artificially—the entrance was too straight, too square. Someone had chiseled it out of the rock.

Bill climbed down into the valley and walked toward it. The cave was shallow—perhaps thirty feet deep. But the walls were covered in paintings.

Rock art. Ancient. The kind you'd expect to find in a Native American site. But these paintings were wrong. The figures were not the stocky, stylized humans he'd seen in Ute and Navajo art. These figures were tall and thin, almost alien. And the scenes they depicted were not hunting parties or spiritual ceremonies.

They showed a sky filled with strange objects—spheres and streaks of light. They showed a great black circle swallowing the sun. They showed figures with weapons that emitted fire.

And at the bottom of the far wall, there was a single image that stopped Bill cold: a man standing in water, reaching toward the sky, with a black spiral above him.

The parasite in Bill's blood pulsed. He felt a wave of dizziness, a flash of something that wasn't memory but felt like it. For a moment, he wasn't in the cave. He was somewhere else—somewhere vast and bright and impossible. A city of glass towers that touched the clouds. Ships in the sky. And then—fire. Everywhere fire. The sky turning black. The ground shaking. People running. A man in a white suit—no, not a suit, a flight suit—standing in front of a wall, painting it with his hands, painting it with his blood.

*"If anyone finds this,"* the man seemed to be saying, *"we were here. We tried. Don't let it happen again."*

The vision passed. Bill was back in the cave, on his knees, sweat pouring down his face, his heart hammering like a trapped bird.

The parasite was quiet. For the first time in six years, it was quiet.

Bill stood up slowly. He looked at the paintings. He looked at the black spiral. He understood now. The thing inside him wasn't natural. It never had been. It was a seed—planted by a man who had come from somewhere beyond the stars, or beyond time, or beyond anything Bill could comprehend. A man who had tried to make humans stronger so they could survive something terrible. And the terrible thing had come anyway. It always did.

Bill walked out of the cave and sat on a rock in the valley. He watched the sunset paint the mountains in shades of orange and red and purple. He felt the parasite sleeping in his blood, a sleeping animal that would wake again, that would keep killing him, that would keep making him something he didn't ask to be.

He didn't know if it was a curse or a gift. Maybe it was both.

He got to his feet and started walking south again. The desert was vast and empty and indifferent. Bill walked into it like a man walking into his own grave.

But not today. Today he was still walking. That was enough.

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