7. Four-Tenths of a Friendship

The old woman's hut smelled of mutton fat and wild onions and the faint, acrid tang of the juniper incense that smoldered in a cracked clay burner beside the door. Liu Gui had to duck to enter, and even inside, the ceiling was so low that his hair brushed the felt lining. Zhang Anu stayed outside with the horses. Li Yuanqing squeezed in behind Liu, his eyes adjusting slowly to the dimness.

The hut was a single room, cluttered with the detritus of a long life. Dried herbs hung from the rafters. Clay pots lined the walls. A loom stood in one corner, its warp threads strung with undyed wool, and beside it sat a wooden chest bound with iron straps that had rusted to the color of old blood.

The old woman knelt before the chest and opened it with a key she wore around her neck. Inside, wrapped in oiled cloth and tied with sinew, was a bundle of birch-bark sheets, each one covered in the angular characters of the Xianbei script. She withdrew the bundle and laid it on the packed-earth floor, then began sorting through the sheets with the practiced hands of someone who had done this many times before.

"My grandmother drew these," she said. "Every detail she could remember. Every passage. Every gear. Every trap. She was afraid she would forget. She was afraid no one would ever find the fourth stomach, and the object would lie in darkness until the mountain crumbled to dust."

Li knelt beside her and studied the diagrams. His craftsman's eyes moved rapidly across the sheets, cataloging, measuring, calculating. "These are more detailed than the schematic on the loom. This shows the gunpowder chamber layout. The charge placements. The detonator connections. And this—" He pointed to a sheet near the bottom of the pile. "This is the ventilation shaft. It's not a shaft at all. It's a natural fissure that runs from the surface down to the sub-chamber. Narrow. Almost vertical. But passable."

"How narrow?" Liu asked.

"Shoulder-width for most of its length. A man could climb down, but he couldn't carry anything bulky. No chests. No sacks of coin. Whatever is in the fourth stomach has to be small enough to fit through a passage no wider than a millet sack."

"That matches what she said. The prince carried it in a saddlebag."

The old woman held up the final sheet. It was different from the others—older, the birch bark yellowed and cracked, the ink faded to a pale brown. The diagram on it was not a map or a schematic. It was a drawing of a box. A simple rectangular container, its surface covered in intricate patterns that might have been writing or might have been decoration.

"This is what the prince carried," she said. "My grandmother saw it once, when the abbot brought it to the fourth stomach. She said it was made of wood that was black as charcoal but harder than iron. She said the patterns on its surface moved when you looked at them too long. And she said it hummed."

"Hummed?" Li looked up sharply. "What kind of hum?"

"A low hum. Like a bee trapped in a jar. She said you could feel it in your teeth."

Li exchanged a glance with Liu. "That could be a mechanism. A clockwork device still running after a hundred years. Or it could be something else. Magnetism, maybe. The old Wei workshops experimented with lodestone. My grandfather had a scroll about it."

"The monks didn't think it was clockwork," the old woman said. "They thought it was alive. Or partly alive. They treated it like a prisoner and a holy relic at the same time. They fed it."

"Fed it what?"

"Oil. Lamp oil. Once a month, the abbot would go down to the fourth stomach with a flask of oil and pour it into an opening in the box. My grandmother never saw the opening. But she heard the box drinking. She said the hum would get louder for a while afterward, then settle back to its normal pitch."

Liu felt the cold creeping back into his bones. He had seen many strange things on the frontier—the mummified corpses the sandstorms uncovered, the lights that flickered over the northern marshes, the sheep born with two heads—but he had never heard of a box that drank oil and hummed.

"We're not monks," he said. "We're not relic-keepers. If this thing is dangerous—"

"It's been sealed in the dark for a hundred years," the old woman said. "It's probably dead. But if it's not dead, it's been waiting. And my grandmother said waiting was what it did best. It waited for the prince to find it. It waited for the abbot to feed it. It waited for the Emperor's agents to hunt it. She said it was patient in a way that no living thing should be patient."

"That's not reassuring."

"It wasn't meant to be."

Li rolled up the birch-bark sheets and tucked them into his tool roll. "We need to move quickly. The failsafe destroyed the treasury chamber, but the gunpowder is still intact. If the primary charge is triggered—by an aftershock, by a cave-in, by anything—the entire sub-level will collapse. We have a limited window."

"How limited?"

"I don't know. The gear train is frozen, but the charges are still live. Old gunpowder is unstable. The longer we wait, the greater the chance of a spontaneous detonation."

The old woman stood and retrieved a small leather pouch from the chest. She pressed it into Liu's hands. It was heavy for its size, and something inside clinked.

"The final key," she said. "My grandmother kept it. The abbot gave it to her when she escaped. He told her to protect it until someone came looking for the fourth stomach. She protected it for seventy-eight years. I've protected it for forty-two. Now it's yours."

Liu opened the pouch. Inside was a bronze cylinder, identical to the one he carried in his boot. Same size. Same patina. Same gear symbol stamped into the wax seal.

"There are two cylinders," he said.

"There were always two. The courier's cylinder held the jade seed and the transfer gear. This cylinder holds the winding key. The mechanism that opens the fourth stomach requires three components, but the mechanism itself—the box, the thing inside it—requires a winding key to operate. My grandmother said the key was separated from the box intentionally. The monks didn't want anyone to be able to use the box without first understanding what it was."

"Use it for what?"

"I don't know. The abbot never told her. But he told her that the box was not a weapon. It was not a treasure. It was a tool. A tool for seeing something that could not otherwise be seen."

Li took the cylinder from Liu's hand and examined it. "Same workshop mark. Same era. This was made by the same hands that made the courier's cylinder." He weighed it in his palm. "Heavier than the first one. The winding key must be substantial."

"Can you open it?"

Li produced his smallest file and carefully cut through the wax seal. The end cap came off, and he tipped the cylinder over his palm. A brass key slid out—not a gear or a seed this time, but an actual key, its shaft square-cut and its bow shaped like a lotus blossom. It was small, no longer than a finger joint, but its craftsmanship was extraordinary. The teeth were cut with the precision of a surgical instrument, and the lotus petals were so finely detailed that Li could see the veins in each one.

"It's a winding key," he said. "For a mainspring mechanism. But it's tiny. Whatever it winds, it's smaller than a pocket watch."

"Or larger," Liu said. "A mainspring can drive anything if it's strong enough. The clockwork in the mountain could have been powered by a mainspring the size of a wagon wheel."

"That would take a key the size of a sword. This is for something delicate. Something portable." Li wrapped the key in a scrap of oiled cloth and tucked it into his tool roll alongside the birch-bark sheets. "We'll know when we find the box."

They left the old woman's hut as the sun was beginning its descent toward the western ridges. The goats had wandered down to the riverbank and were nosing at the frozen reeds. Zhang had built a small fire and was heating millet cakes on a flat stone. He looked up as they approached, and his expression was guarded.

"Well?" he asked.

"We have maps," Liu said. "And a key. And a story about a box that drinks oil and hums."

"Sounds valuable."

"Sounds dangerous."

"Same thing, in my experience." Zhang handed Liu a millet cake. "Eat. We have a long ride back to the mountain."

They ate in silence. The millet cakes were bland and gritty, but they were warm, and the warmth spread through Liu's chest and into his limbs. He thought about the old woman's grandmother, a nine-year-old girl crawling through a ventilation shaft while imperial agents sealed her family inside a mountain. He thought about the abbot, pouring lamp oil into a box that hummed. He thought about the Sasanian prince, dead on a frontier road, his saddlebag stolen by the very men who had been sent to protect him.

And he thought about the Empress. Wu Zetian, the Divine Empress, the only woman ever to rule China in her own name. She had seized the throne in a river of blood, and she had held it for a decade against all challengers. If the box in the mountain was as powerful as the old woman suggested, the Empress would want it. But would she reward the men who brought it to her, or would she bury them alongside it?

"We should discuss something," Liu said, breaking the silence. "Before we go back into that mountain."

Zhang looked up. "Discuss what?"

"What we're actually going to do with whatever we find. The old woman said the box was meant for the Great Wild Goose Pagoda. For the Buddhist monastery. But we're not monks, and we're not relic-keepers, and we have a death warrant hanging over our heads. If we deliver the box to the monastery, we get nothing but merit in the next life. If we deliver it to the Empress, we might get pardons. Or we might get executed."

"There's a third option," Zhang said. "We find the box. We find out what it does. If it's valuable, we sell it."

"Sell it to whom?"

"Whoever wants it most. The Empress. The monks. The Secretariat. The Directorate. There's an auction happening whether we're there or not. The only question is whether we're bidding or selling."

Li shook his head. "If the box is what the old woman says it is—something the Sasanian empire fell over, something the Wei monks died to protect—then selling it to the highest bidder might not be something we can control. What if the buyer uses it? What if it's a weapon after all, and we've just sold it to the wrong side?"

"Then we make sure we sell it to the right side."

"How do we know which side is right?"

Zhang had no answer for that. Neither did Liu.

They mounted their horses and rode west, back toward the ox-shaped mountain. The sun sank lower, painting the snow in shades of gold and rose. The goats scattered before them, bells clanking, and the old woman stood at the door of her hut, watching them go with her ancient, knowing eyes.

By nightfall, they had reached the base of the mountain's eastern slope. The fire from the failsafe had burned itself out, but the smell of smoke still hung in the air, and a faint haze drifted across the stars. The ox's spine loomed above them, a black silhouette against the indigo sky, and somewhere on its flank, hidden beneath a granite slab, was the entrance to the ventilation shaft.

"We should wait until dawn," Li said. "Climbing down a narrow fissure in the dark is a good way to break a leg."

"We don't have until dawn," Liu said. "The gunpowder is unstable. Every hour we wait increases the risk."

"Every hour we rush increases the risk of falling."

Liu dismounted and began searching the slope. The juniper grove was gone, burned to stumps, just as the old woman had said. The granite slab should have been visible, but the snow had drifted against the mountainside, burying everything under a white blanket that glowed faintly in the starlight.

"The slab has an iron ring on its underside," Liu said. "We need to probe the snow. Find the slab's edges."

They searched for an hour. The cold intensified as the night deepened, and their breath froze on their eyebrows and lashes. Zhang cursed steadily under his breath. Li worked in silence, methodical as always, using his walking stick to probe the drifts.

It was Li who found it. His stick struck something solid that rang with a dull metallic note. He knelt and dug through the snow with his bare hands until he exposed a corner of the granite slab, its surface rough-hewn but its edges cut square.

"Here. Help me clear it."

They dug together, and gradually the slab emerged from the snow. It was larger than Liu had expected—twice the width of a man's shoulders and half again as tall. Its surface was carved with the same Xianbei characters they had seen throughout the cave complex, but these were different. Older. More angular. Li studied them by the light of a small oil lamp he had taken from his pack.

"It's a warning," he said. "Or a blessing. I can't quite tell. 'Let the one who descends know that what was sealed was sealed for a reason. Let the one who opens know that what was opened cannot be closed again.'"

"Another riddle," Zhang muttered. "I'm getting tired of riddles."

"Riddles are just instructions written by people who don't trust the reader," Li said. "Help me lift it."

The slab was heavy, but it was balanced on a pivot stone, and once they found the iron ring on its underside, they were able to lever it upward with a fallen juniper trunk used as a fulcrum. The slab rose with a grinding sound, and beneath it was a hole—a dark mouth in the mountainside that exhaled a breath of cold, stale air.

The ventilation shaft.

Liu lowered the oil lamp into the hole. The fissure descended at a steep angle, its walls rough and glistening with frost. After about ten zhang, it opened into a wider space—the sub-chamber that the old woman's grandmother had described. He could see the glint of bronze on the walls. Gears. More clockwork.

"I'll go first," he said.

"No," Li said. "I should go. If there's machinery down there, I'm the one who can recognize it. If there's a trap, I'm the one who might be able to disarm it."

"If there's a trap, you're the one we can't afford to lose."

"Then send Zhang."

Zhang laughed. "I'm not climbing down a hole in the dark while you two argue about who's more valuable. Liu goes. He's the commander. He's been making the decisions since the relay station. One more won't hurt."

Liu nodded. He tied a rope around his waist and anchored it to the granite slab. He tucked the oil lamp into his belt. He checked his sword, his knife, the bronze tube in his boot. Then he lowered himself into the fissure.

The descent was slow. The walls pressed against his shoulders, and his boots slipped on the frost-slick stone. The rope bit into his waist. The oil lamp swung from his belt, casting wild shadows that made the fissure seem to writhe around him. He descended hand over hand, counting his breaths, focusing on the mechanical rhythm of the motion.

Ten zhang. Fifteen. The fissure widened, and suddenly he was dangling in open space. The sub-chamber. He swung the lamp around and saw what the old woman's grandmother had seen a hundred years ago.

It was a small room, circular, its walls lined with bronze gears that were still and silent. In the center stood a stone pedestal. On the pedestal sat a box.

The box was black. Not the black of painted wood or tarnished metal, but a deep, absolute black that seemed to swallow the lamplight rather than reflect it. It was rectangular, about the size of a soldier's mess tin, and its surface was covered in patterns that Liu could not quite focus on. Every time he tried to trace a line, his eyes slid away, as though the patterns were moving just beneath the surface of the wood.

And it was humming. A low, steady hum that vibrated in his teeth and in the bones of his skull. It was the hum of a bee trapped in a jar. It was the hum of a mainspring that had been wound for a hundred years and was still waiting to be released.

Liu lowered himself to the chamber floor. His boots touched stone, and the sound echoed strangely in the confined space. He approached the pedestal slowly, the hum growing louder with each step. The box did not move. It did not glow. It did not do anything except sit there, humming, as it had been humming since before his grandfather's grandfather was born.

"Liu?" Li's voice echoed down from above. "What do you see?"

"A box," Liu said. "Black. Humming. Covered in patterns that don't stay still."

"Don't touch it. I'm coming down."

Li descended the rope with the speed of someone who had spent his childhood climbing through workshop rafters. He landed beside Liu and immediately knelt before the pedestal, his eyes bright with the intensity of a scholar confronting a text he had spent his whole life hoping to read.

"The patterns," he breathed. "They're not decoration. They're writing. Sasanian cursive. The old Persian court script. My grandfather had a fragment of it in his workshop. He said it was the most beautiful writing he had ever seen, and the most dangerous."

"Dangerous how?"

"The Sasanian kings used it for their secret correspondence. The script was designed to be unreadable to anyone who hadn't been trained in it. The letters shift depending on the angle of the light. That's why the patterns seem to move."

"Can you read it?"

"No. No one can, except maybe a handful of scholars in Chang'an. But I recognize the structure. It's a set of instructions. Or a warning. Or both."

Liu looked at the box. It sat on its pedestal, humming its patient hum, its surface crawling with letters that no one alive could read. It had traveled a thousand li on the back of a dead prince. It had been fed lamp oil by a dead abbot. It had been sealed in darkness by dead monks. And now it was waiting for three dead soldiers to decide what to do with it.

"Li," Liu said. "The winding key. The old woman said the box needs to be wound."

"You want to wind it? We don't know what it does."

"We came here to find out. If we bring an unwound box to the Empress, she'll have her own engineers wind it. If it's dangerous, better we find out now than let them find out in the middle of Chang'an."

Li hesitated. Then he withdrew the brass key from his tool roll and approached the box. The hum intensified as he drew closer, as though the box could sense the key. He knelt beside the pedestal and examined the box's surface, searching for a keyhole.

He found it on the bottom. A small opening, square-cut, just the right size for the winding key. He inserted the key, and it fit perfectly, sliding into the mechanism with a soft click.

"Should I turn it?" he asked.

Liu thought about the old woman's prayer. She had prayed for whoever would open the fourth stomach. She had prayed they would be strong enough to carry what they found.

"Do it," he said.

Li turned the key. Once. Twice. Three times. The mechanism inside the box began to tick, a soft, rapid sound like a heartbeat accelerating. The hum rose in pitch, climbing from a low drone to a clear, pure note that seemed to resonate with something deep in Liu's chest.

And then the box opened.

It did not open like a normal box, the lid swinging upward on hinges. It unfolded, the panels sliding apart in a precise mechanical sequence, revealing what lay inside.

It was a sphere. A perfect sphere of some material that was neither metal nor stone nor glass, but something between all three. It was translucent, and inside it, suspended in a clear fluid that might have been oil, was something that pulsed with a faint blue light.

A heart. Or something that looked like a heart. It was the size of a child's fist, and it was beating. Once every ten seconds. Slow. Steady. Patient. As though it had all the time in the world.

"What is that?" Liu whispered.

Li stared at the sphere. His face was pale, but his eyes were shining. "I don't know. But I think it's alive. I think it's been alive for a hundred years. And I think it's been waiting for someone to wake it up."

The heart pulsed. The blue light flickered. And somewhere in the walls of the sub-chamber, the bronze gears began, very slowly, to turn.