Since time before record, the worlds of Ki and Kur have been entangled. Every fourth day, the boundaries of space and time are disturbed, so that each world is seemingly transposed with the other, and an alien sun rises in its sky, with catastrophic results. The light of Kur’s star is deadly to the life of Ki, and vice versa; every contact between the creatures of the two worlds likewise produces only violence, corruption, and decay. Yet contact is frequent enough, on the fourth day when the barriers put up by nature are thin and porous. Over many years each world has been colonized by invaders born under its enemy’s sun, spreading disease and death.

Civilized life still exists on Ki, but only at great cost. For those who are unwilling or unable to pay that price, there are other ways to live—but they are far from pleasant.

Ram adjusted the cloth over his face before he went down the tunnel. It was burning hot, a bright and early morning under the yellow sun, and he was slick with sweat beneath his layers of cloth and leather armor. The hilt of Father’s bronze sword was slippery in his right hand; the enormous shield on his left arm felt far heavier than it was. Even so, he’d wrap his face up tight, and be grateful for it. The stench at the top of the tunnel was appalling, a mix of dung and rotting meat. It would only be worse farther in. And if he got any of the resh slime on his bare skin, that would be worst of all.

It was amazing how long this place had passed unnoticed, given the sheer stink it gave off. They’d been able to smell it from half a mile off, before they’d even seen the low mound, like an anthill, rising out of the dusty plain. It was five miles from the hearth, out in the desert wastes where the god’s light didn’t shine. Up close, it was less an anthill than a great sore in the earth, a wound crusted over with the filth of the vermin who made it. He didn’t want to know what the black gunk was that held the dirt of the roof together.

The men of Urapu hearth were bound by law to keep watch for infestations. Everyone knew what reshki could do. But they’d had no clear reason to check all the way out here, and the men of his hearth were always busy. There were crops to tend, and walls to mend, and they’d had no resh troubles for whole kindlings, since before Ram was born. So they’d gotten complacent. There was no other word for it.

Complacency could get you killed, and it had. Five men, two women, and a child barely old enough to walk, and that was just the dead. There were also the wounded, and the maimed. Like Father. Father hadn’t even been on duty, the day the reshki came leaping over the walls under the pale and deadly light of the white sun. But he’d come out, unprotected, swinging his hammer, all the same.

He’d only killed one, before its friend clawed him right down the arm. For two days they’d struggled to save it, but the black, stinking corruption kept creeping up. Last night Mother agreed to let them cut it off at the shoulder. It had taken five minutes. Five minutes of screaming through the gag, then a terrible cold silence while they carried the tainted limb off to burn. Ram hadn’t known for sure that Father survived it until early this morning.

And then, while he was wandering about the hearth in a daze, he’d heard the call for volunteers. They’d found the nest. The reshki were licking their wounds after their losses, but they’d be back; the white sun would rise again tomorrow. The men of Urapu hearth had to destroy the threat, before it destroyed them. Who, they asked, was a man of Urapu hearth?

Ram was fourteen; he’d be an adult in a few months. And Ninnara and the other girls were watching. He’d raised his hand. Watchmaster Kambuz had blinked, but only asked if Ram had weapons and armor. “I can use Father’s,” he’d said, and they mostly fit. He was almost as big as Father now, after all, and he had muscle from helping Father at work. Kambuz had agreed, in public, in front of the whole hearth. Mother couldn’t make him back down after that, no matter how angry she was. The family’s word still meant something, and Ram was old enough to give it.

Which left him standing at the top of a dank tunnel, with a rag over his mouth, waiting to go down into a dark hole packed with who knew how many reshki. He didn’t have to go down very far, just far enough to be sure of blocking the tunnel, preventing an escape. But he did have to go down; the hearth was counting on him. Every one of the other five exits would have a man in front of it. A single survivor, if it was female, could restart the whole nest.

The yellow sun beat down on his neck. It would be cooler inside the nest, he told himself. Reshki dug deep, to get away from the light they hated. And they would all be sleeping now. He would go down a little bit, just enough to get in the shade, but still have the sunlight shining from behind him. He didn’t want to go down too far, after all. In a few minutes, the center of the nest was going to become very unpleasant.

One step. Then another. Then a third. He stopped.

The ground underfoot was faintly sticky, a mixture of dust and foul excretions baked into a gummy consistency by the heat of day creeping in. He could hear flies buzzing ahead, but could not see them. They were shunning the light, like reshki. Not ordinary flies, then, nothing natural to Ki. These were vermin bred in resh-corpses. They were kurtushi, corrupted. If one bit him, or even touched him, he’d be contaminated. And then they’d have two cripples in the family—if he was lucky.

It was almost time, he thought. They would take a while longer getting the ladies into place; they were risking half of the hearth’s six handmaidens on this, to burn the miserable freaks out of hiding. Naturally all three handmaidens would have to be heavily guarded, and their protectors would pull them back the moment they scented a bit of trouble. If those three women were killed, the hearth would be ruined. Boys like Ram were more expendable; of the fifteen watchmen who came out to this hole, Kambuz had chosen the six least important to watch the exits. Like Rammash, son of the vagabond mason.

He sheathed the sword, just for a moment, to wipe the sweat off his palm. Even through the cloth, the smell was horrible; the little air that came through felt like it would soil his lungs. But not for much longer …

Ram saw the flash of golden light at the same instant he heard the first squeal of alarm. At least one resh had been awake. It didn’t matter. The squeal turned into a series of shrieks as he drew Father’s sword again. Just shrieks, none of the war-cries he’d heard three days ago. More flashes came up from below, together with a smell of charred meat and bone that was positively refreshing by comparison. They had no idea how the tunnels were laid out down here, but they hardly needed to. As long as the handmaidens kept channeling the hearth’s holy fire into the center of it, and there were men with swords at every exit, the few who didn’t burn or tear each other apart in a panic would be cut down as they fled.

Ram had only a half-second’s warning, a glimpse of shifting shadows and a clatter of claws in the darkness below. He raised his shield just in time for something small and fast to slam into it and knock him flat over on his back. His head smacked against the filthy floor hard enough to blur his vision even through the helmet. The weight of the resh bore down on his shield for an instant, then lifted as it sprang off over his head and up the tunnel.

It took an agonizing three seconds for Ram to shake his head clear and force himself back to his feet. He stumbled back up into the light—where was the resh? It was his job to prevent escapes, and he’d already failed. What if it was a breeder?

The world outside was a long, monotonous stretch of brown dust and sickly weeds. They were far from the hearth, and the nourishing light of its holy fire. Everything that lived out here was kurtushi, or else barely holding on. Three days under the kindly yellow sun, one under the deadly white one—a plant could survive that brutal cycle, but it would never thrive. Now the yellow sun was shining hot and bright in a clear blue sky; where was the resh? He trudged off over the sand.

It hadn’t gone as far as he feared. The yellow sun of Ki was as horrible to reshki as their white one was to humans. And it was wounded. He caught the whiff of burnt meat from some ways off, and followed it to a little stream. It was half-submerged in the shallow water, trying to splash some over its back with its clumsy clawed hands.

The resh hadn’t noticed Ram yet. Now would be a fine time to sneak behind it and finish it off. But it was in water, and the water would already be tainted; if he attacked it there, he would be splashed, and some of the filth would seep through his rags. So he hung back to study it for a moment.

It was more human than he’d expected. Small, barely bigger than a five-bloom-old really, but it looked more like a human than any other creature. Or perhaps a monkey or ape? He’d seen a monkey once, the pet of a traveling flutist who visited the hearth last summer. He’d taught the animal to dance as he played. This resh was only a bigger, tailless version, with shorter, more bristly black hair. The skin underneath was a pale greyish-white.

Ram guessed it was a young one; not only was it small, it was still healthy. The older ones rotted quickly, and fell apart before they turned ten if their families didn’t kill and eat them first. Or so he’d heard. Everyone said Reshki only survived by breeding faster than the corruption could take them. A young resh would be quicker and tougher than an old one, but also less toxic. They’d told him one of the eldest would pop like a fermented fruit when you cut it, spraying infected liquid and parasites everywhere. You had to kill those by throwing rocks.

At any rate, this one had a big black burn all across one flank. Third-degree. It would die soon even if he didn’t touch it. It might even be a kindness to kill it more quickly, and he’d never want to show kindness to a resh. But he had a job to do, and it wouldn’t get done if he stood stalling at the top of a streambank while the monster bathed. He thwacked his sword against the boss of his shield, making a sound like a bell.

The resh sprang out of the water at once. Before the gong had died down, it was turned around on the opposite bank, sunk low to leap and kill. Two pairs of breasts dangled off its chest; it was a breeder, all right. He’d been right to chase it—but it was still humiliating to get knocked down by a little girl.

It didn’t matter now. He had his shield up now, and his sword ready. The resh was squinting in the painful light, and whining something at him. It sounded like they were supposed to be words, and they probably were, but he didn’t speak resh. What human did? “Come on,” he told it. “You’re dead anyway. Let’s make it quick.”

It obliged, far faster than he’d expected. There were at least fifteen feet between them, but the resh covered most of the distance in a single leap, landing just under Ram’s feet and bulling up into him. He was prepared this time, braced against the bank, and he swung out with the shield to slap it back down the bank.

It rolled as it fell, came to a stop in the mud by the water’s edge, and lunged once more almost before Ram had his shield back in position. This time the resh aimed high, trying to leap over the shield, and it nearly succeeded. Ram’s clumsy swing caught it, but only with the flat. It squealed anyway—he’d caught its burnt flank—and fell to the ground thrashing. Ram’s next swing sliced its ankle open. Then it was back out of range, limping down to the stream’s edge.

“No more jumping,” he told it. It snarled something back, but without turning its head. Was it trying to run away? That wouldn’t work either, but he’d have a miserable time trying to slice it to bits as it dodged and ran. Even hurt, it was at least as fast as he was, and far lighter.

Now it was in the water, wading down the stream. Well, it wasn’t stupid. It knew he wouldn’t want to get wet. But the water also slowed it down. Ram could keep pace easily, or even get a ways ahead. In fact … he looked downstream. There wasn’t much growing along the bank, but there was a stunted tree up ahead. Six or seven feet tall, with only a couple of browning leaves dangling from its branches. Perfect.

Ram sheathed the sword and sprinted, as quickly as he could in his smothering gear. He’d got a good ten feet on the resh by the time he reached the tree. A few seconds’ tugging had it uprooted; the soil was thin, and months of work with Father had made him strong. The resh hesitated, a moment too long, then tried to surge forward. Too late. The root-end of the tree came down on its back like a hammer, still weighted with clumps of dirt and little rocks.

Ram let it rest on the creature’s back a moment, watching it struggle to lift its head out of the water against the weight. The muddy roots would only get heavier as they absorbed the damp. Still it pushed and strained. When it was nearly free, and taking its first gasping breaths, he lifted the tree back up and swung it down on its head.

The resh took a long time working free again. As soon as it did, it scrambled its way up the opposite bank, ignoring repeated blows to the back. Ram flung the tree aside, picked his shield back up, and jumped the stream. The resh was half-drowned, weary, sick, battered, and burned. But it kept limping on with its three good limbs.

Ram’s first cut caught it across the buttocks, knocking it flat. The second hit the small of its back as it struggled to rise. The third was a jab right into the burn. Then the belly. The right arm, raised to shield it. The face, as it tried to cry. The throat, a bare scratch as it twisted away, yearning to live. The shoulder. The other shoulder. The belly again. The thighs.

And then it was still, more or less, only shuddering and bleeding out as it tried to move too many broken parts at once. Their eyes met. Its eyes were too human for comfort. But Ram could remember the child, the little girl this creature’s brothers had ripped to bits a tetrad before. They’d had trouble finding enough to cremate for the funeral. She’d been more human than this thing.

Ram flipped it onto its back with his sword’s tip, placed it between the four breasts, and pushed down with all his weight until he felt it grind past the resh’s spinal column. It gasped, spasmed, and lay finally, totally, still.