Mara struck stone with her shoulder, slid across it, and caught a chain before the dark took her.
The links snapped taut under her arms. Below, furnace light spilled through a widening cleft in the floor. It showed brickwork, iron teeth, and a passage descending at an angle steep enough to break a body before it reached the bottom.
Teren had one hand around her wrist.
His other hand gripped an iron staple beside the slab. Blood ran over his knuckles where the staple had stripped the skin. His boots scraped for purchase on the tilting floor.
"Let the chain go," he said.
"It is holding me."
"It is feeding into the wheels."
She looked down. The chain vanished between two turning cogs. Link by link, it drew her toward them.
Mara released it.
Teren hauled her against the slab as the chain whipped away. Its free end struck sparks from the brick and disappeared into the mechanism with a sound like a spoon dropped into a mill. The cogs bit. Iron screamed.
Ivo landed beside them on one knee, caught Sabine by the back of her coat, and dragged her clear of the splitting floor. He did it with no courtesy at all. Sabine's sleeve tore from shoulder to cuff.
"That pin," Ivo said, breathing hard. "Did it have a second instruction engraved on it? Kill every Rusk in reach?"
"Only the deserving ones," Mara said.
The furnace draft changed. It no longer pulled toward the chimney. Air rushed downward through the opened passage, carrying the hot mineral stink of scale, wet mortar, and old lamp oil.
Not a tomb, then. Tombs did not require oiled machinery.
The stone beneath Teren's boots lurched again. He shifted his grip from Mara's wrist to her forearm, avoiding the joint, and lowered her onto the narrow ledge beside him before attending to his own balance. It was a cavalryman's movement: exact, practiced, sparing her the indignity of being flung where he wanted her.
His hand left a red print on her sleeve.
Mara stared at it for half a breath too long.
Above, men shouted in the hidden works. Someone called Sabine's name. The answer came as three blows against the kitchen door.
Sabine pulled her torn coat closed. "The gate passage has opened. We must shut it before the pressure reaches the lower flues."
"You said it would vent," Mara replied.
"It has."
A seam in the furnace wall glowed orange. Mortar cracked and spat white fragments.
"That is not venting. That is a vessel preparing to remove its own walls."
"Then you had better be as competent as your indictments claim."
Ivo gave Sabine's coat another hard pull, turning her toward him. "Where does the passage go?"
She looked at his fist until he released her. "To the lower boundary road."
"There is no lower road."
"There is when the river is high."
Mara knelt at the ledge. Through the opened slab she could see rails descending beside the cogs, their tops polished by recent use. A smear of green grease shone on one rail. Fresh. The pressure gate had not slept beneath the house for thirty-seven years. Someone maintained it.
A copper pipe ran along the passage wall, branching at each iron tooth of the mechanism. Its nearest joint shivered. A pale crust had formed around the seam.
Mara touched one grain to her damp fingertip. Bitter salt whitened the whorl of her skin.
"Cooling brine," she said. "The line has emptied."
Teren wiped his bleeding hand against his coat. "Can you close the gate?"
"Not from here. The release has engaged every tooth below us. I can stop the furnace or reset the pressure."
"Which keeps the house standing?"
"That depends which part of the house you value."
A timber split overhead. Dust poured from the ceiling. Behind the kitchen door, the men began using a ram.
Sabine stepped toward the nearest control ring.
Mara caught her wrist. "Touch that and the counterweight drops."
"Yes."
"With us above it."
"You have always been quick when consequences concern you personally."
Teren moved between them without taking Mara's hand from Sabine's wrist. He did not command either woman to release the other. He merely placed himself where Sabine could not reach the ring and Mara could not be struck without striking him too.
It was infuriatingly effective.
"The lower controls," he said. "Can they reset it?"
Sabine's gaze flicked toward the descending rails.
That was answer enough.
Ivo looked into the passage. "I'll go."
"You do not know the valves," Mara said.
"You can shout. You do it clearly."
"The air below will be furnace-hot and poor in breath."
"Then make the instructions short."
Teren pulled off his neckcloth and wrapped it around his palm. He used his teeth to tighten the knot. "I go with her. You keep the stair."
Ivo's face closed. "You gave away command. You don't give me posts now."
"No. I ask you to prevent those men from driving us into a furnace."
The ram hit again.
Ivo drew his knife, tested its edge with his thumb, and offered it handle-first to Teren. "For the ropes below. Mine is sharper."
Teren took it. Neither brother looked at the other.
Mara lowered herself over the ledge. The iron rail burned through her skirt. Teren descended after her, one arm braced above her shoulder to take the weight if her boots slipped. Sabine followed without asking leave.
"You stay," Mara said.
"It is my house."
"At present it is a heated pressure vessel with curtains. Ownership is not a useful qualification."
Sabine stepped down beside her. "Nor is insolence, yet you have made a profession of it."
They descended.
The passage narrowed until Mara's shoulders nearly touched both walls. Heat thickened the air. The rails ended at a stone platform beside a counterweight taller than a man. Ropes passed through its iron crown and into darkness. Beyond it stood three valve wheels, each marked with a household cipher: Veylan, Rusk, and the crowned calipers of the Office.
Mara stopped.
Teren's chest touched her back before he checked himself. Even through coat and stays she felt the hard interruption of his breath.
Sabine said, "The centre wheel. Two turns against the crown."
"You knew there was an Office control."
"Every lawful boundary work has one."
"Lawful works are recorded."
"Recorded things are more easily taxed."
The copper cooling line knocked in the wall. Once. Twice.
Mara went to the centre wheel. A locking bar held it in place. The bar had been fitted with a small brass housing, blackened at one side by chemical smoke.
She bent close. Bitter almonds under hot oil. Sleep-smoke residue, heavily washed but unmistakable. Her formulation used gum resin to slow the burn; it left a violet-brown glaze on brass. There it was, caught beneath the hinge.
Teren saw her face change. "What is it?"
"My work."
Sabine's fingers tightened on the torn edge of her sleeve.
Mara scraped the glaze with Ivo's knife. The shaving curled like old varnish. "This lock was opened with smoke made to my proportions. Not the crude compound from the gate crates. Mine."
"Can you open it now?" Sabine asked.
Mara turned. "Who supplied them?"
The furnace gave a deep concussion. Flame breathed through the mortar joints, blue at the edges. Teren seized the rope above the counterweight as it jerked downward. The wrapped hand failed him. He changed hands without a sound and wound the rope around his forearm.
"Mara," he said, very evenly. "The question survives us only if we do."
She put the knife under the brass housing. The lock had been designed to resist picks, not leverage. She drove the blade with the heel of her hand. Brass bent. A glass capsule cracked inside, releasing a thread of sweet vapor.
Teren pulled her backward against him and covered her mouth with his blood-wet neckcloth. With his injured hand he stripped off his coat and flung it over the lock.
He had smelled it almost as quickly as she had.
Mara could not stop noticing that.
"Hold your breath," she told Sabine through the cloth.
Sabine had already covered her nose with her sleeve. Her eyes watered, but she remained upright.
Mara reached beneath the coat, found the locking bar by touch, and tore it free. The centre wheel spun half a turn on its own. She caught a spoke.
"Help me."
Teren took the opposite spoke. His palm soaked the cloth red.
They turned together. The wheel fought them in short, brutal increments. On the second turn, cooling brine thundered into the pipes. Steam burst from the wall and filled the passage with white heat.
The counterweight dropped.
Its rope snapped across Teren's forearm and dragged him off his feet. Mara caught his belt with one hand. The wheel kicked against the other, wrenching two fingers backward. Sabine seized the spoke before it could reverse.
"The lower catch," Mara gasped. "By the floor."
Sabine looked down. A narrow iron lever shuddered beside the counterweight, already sinking beyond reach.
She thrust her arm between the descending weight and the wall.
Her hand closed on the lever.
The counterweight struck her forearm.
There was no dramatic crack. Only a dense, wet sound, and Sabine's breath leaving her through her teeth. She pulled the catch anyway.
The mechanism stopped.
For several seconds the passage held nothing but steam and Sabine's shallow breathing.
Teren freed himself from the rope. He knelt beside her and examined the trapped arm. His own sleeve was cut open to the skin, but his fingers remained careful. He did not tell Sabine it would be well. He did not offer a lie because she was hurt.
"The weight must rise before we move you," he said.
Sabine's face had gone grey. "Then raise it."
Mara looked at the three wheels. The Veylan and Rusk controls were chained. Only the Office wheel moved, and the broken lock beneath Teren's coat continued to breathe her own sweet poison into the stone.
On the inside of the bent brass housing, protected until she forced it open, someone had stamped a maker's line.
Not an Office number.
Her laboratory number.
The one she had cut into molds herself, beneath the estate, where no buyer had ever been permitted to see it.
Mara wiped steam from the stamp with her thumb.
"Who entered my laboratory?"
Sabine shut her eyes.
Above them, the kitchen door broke inward.
"I did," she said. "The night before I gave its location to Pell."