Mark pressed his back against the wall and counted hunger pangs instead of hours. Three days, give or take. He just wanted to go home, to walk back into the warehouse and find his three friends still arguing about the shot. Instead, he was here, in a grey place he had basically written into being. He noticed the yellow first on the little house he had been using as shelter. A damp patch bloomed across its cheerful pink siding, eating the paint. The orange door sagged. His safe spot was rotting in front of him. Then he saw the rest. A tall light post nearby was wrapped in thick yellow tendrils, glowing sickly bright. His old film camera, the one he had found and hauled around like a lucky charm, sat half-drowned in the same yellow sludge. The air grew thick. Each breath tasted like wet pennies. Mark coughed and stumbled back. A shape moved at the edge of his vision. A dog, yellow-furred and too still, watched him with human eyes. Behind it, something taller unfolded itself from the haze — a thin black figure with a bulbous, potato-shaped head, twitching like a bad puppet. He ran. He did not pick a direction. He just moved, lungs burning, away from the house, away from the spreading stain. He ran until the air thinned and the yellow glow faded behind him. When he stopped, his shelter was gone. The camera was gone. Everything he had gathered in three days — gone. Mark stood alone on flat grey ground, gasping. He had escaped. He had also lost the only place he had made his own. Whatever was chasing him now had a face, and it knew where he had been.

Mark crouched on the flat grey ground and forced his breathing slow. Running blind had almost cost him everything. If he moved again, he had to move smart. He needed to know where the things behind him had already been, so he could go anywhere else. He found their trail by accident. A long smear of dried yellow crust ran along the ground, pressed with claw marks and a deep, dragging groove. It looked like armored tracks, curved and heavy, scraped into the dust by something built low and wide. The crust glowed faintly. Wherever it led, they had been. Mark turned his back on it and picked the opposite way. He still felt exposed. So he doubled back to the edge of the corruption and pulled loose a matted hunk of yellow fur from a dead patch of growth — sticky, bright, awful. He smeared it across his jacket and hood. If their eyes hunted for grey movement, he would be the wrong color. If they hunted for yellow, he would be one of the herd. It was disgusting. It was also quiet work. Moving low, he spotted it in the distance: a huge pale structure rising from the flatness, lit by a soft blue glow that the yellow seemed to bend away from. Mark pressed himself against its cold stone wall and finally exhaled. He did not know what the building was. But the hunters were behind him, their path mapped in his head, and for the first time in three days he had chosen a direction instead of fleeing one.

Mark pressed his back to the pale wall and let the blue light wash over him. His breath finally evened out. The hunters were somewhere behind him, mapped and avoided. For one small moment, the wall at his spine felt like safety. Then something on the ground near his boot clicked. He looked down. A sleek metal device sat half-buried in the dust, its center panel pulsing a soft pink. He picked it up. The pulse quickened. The pink deepened to a hot, alarm-bright red, throbbing against his palm like a second heartbeat. He lifted his eyes slowly. Across the flat grey, a tall black figure had stepped out from behind the pale structure. Its grotesque potato-shaped head turned in slow, searching arcs. Wisps of grey smoke curled where its feet touched the ground. If it rounded the wall, his only shelter became a trap. Mark turned the other way and ran low. The device burned red in his fist. He scrambled around a low ridge and stopped short. A building sat there that did not belong — sleek, angular, plated in metal, with a yellow hexagon glowing above a heavy door. It looked built in a lab, dropped into the dust. Test towers. A stamped name plate. Something made for experiments, not for this dead world. He shoved against the door. It gave. Mark slipped inside and pressed it shut behind him. The red pulse in his hand slowed, then dimmed to a steady pink. He had lost the pale wall. He had found something stranger, and someone, somewhere, had built it on purpose.

Mark stood with his back to the door, breathing hard. The pink pulse in his fist had calmed, but his head had not. The inside of the building was bright and clean. A sleek laptop hummed on a low table, its screen looping diagrams of past experiments. Wires ran along the floor like roots. Someone had built this room to study something. He just did not know what yet. He stepped deeper in. A wooden bulletin board hung on the far wall, papers pinned in neat rows. The banner across the top read TEST FINDINGS. Below it, in shaky marker: THIS IS A TEST PLACE AND THIS IS WHAT WE FOUND OUT. Mark read the notes one by one. Air samples. Bacteria counts. Warnings about something in the dust outside. His stomach dropped. He had been breathing it for three days. In the corner sat a heavy yellow suit on a stand, a black gas mask hanging from its hood. Beside it, a clipboard listed names crossed out one by one. Someone else had been here. Someone else had tried. Mark's hands shook as he unzipped the suit and climbed in. The mask sealed with a soft hiss. The world through the visor went a shade darker, but his lungs, for the first time, felt clean. He understood now. The building was not a door home. It was a lab, and the dimming device was only telling him the air inside was safe. The way out was still out there. But this time, when he stepped back through that door, he would not be breathing the poison alone.