Saya would not let Marek choose a memory at random.
She closed the depot door, posted two witnesses by the stove and ordered Irsa away from the casing. The external node had to distinguish the operator's will from other voices. For that it needed neither a secret nor an important fact, but a living sensation that could not be mistaken for anyone else's.
"A name won't do," Saya explained. "You can hear it from someone else, and see your face in another person's memory. You need a moment in which you were unmistakably yourself."
Marek suggested his first day on the railway. Saya asked what he had felt then. He remembered Beran's pride, the weight of the tools and the smell of hot metal. None of it belonged only to him.
Then he named his last conversation with Ella.
Irsa flared brighter.
Saya refused at once.
"You don't remember the whole conversation. The emptiness around it is already drawing in other people's guesses and everything you invented later. The node would receive a wound, not a key."
Marek grew angry because she was right. He remembered five knocks on the kettle, smoke in the corridor and a closed door. He had spent years filling in everything else himself.
Then Beran asked what the house had been like before the fire.
The answer came as a smell.
Wet firewood beside the stove. Apple peel at the edge of the table. The iron of the old kettle, which smelt stronger when the water boiled away. In winter Ella dried her mittens too close to the fire, and the smell of wet wool mingled with the smoke.
Marek could not see the whole room, but he knew that if he caught that smell, he could enter it in the dark and find his bed.
Saya asked him to repeat the memory three times. The details did not change.
"It will do," she said. "While the node is open, you won't be able to enter this memory of your own will. If we close the link properly, it will return. If the salt erases the key, nothing will return."
"I'll forget the house?"
"You'll know it existed. But you won't recognise its smell."
Marek looked at the map. In the Soot, eighteen people were breathing through the last plates, the water had risen another step, and the Salt Guard was already searching for the dead branch line.
He placed his palm on the stove.
Irsa moved between his fingers and the metal. For a moment Marek felt her offer another key: Ella's five knocks. He snatched his hand back.
"No. It isn't wholly yours or mine."
The cold spark did not argue. She moved aside.
Marek gave up the smell of the kitchen.
The memory did not disappear at once. First the wet firewood became mere damp. Then the apple peel lost its sweet bitterness. Last to go was the heated metal of the kettle. Marek could still see the table, the stove and his sister's small hands, but the room had become airless.
A red line appeared on the casing. It circled the stove, ran down the pipe and divided into twenty-four slender branches.
"External node open. Local limit: twenty-four lines. Operator's direct limit: twelve lines."
Synchronisation took seven minutes. Throughout that time Irsa lay at the centre of the red line, repeating the rhythm of Marek's heart. Saya made sure no human echo from the sealed vessel entered the node.
In the sixth minute, salt chimed in the far tunnel.
Yuna heard it first. She tore the red thread from the wall and retied the knot around another pipe. It meant the route was no longer safe.
Beran sent two workers to the northern entrance and the rest to the drain shaft. The people could not defeat the reconnaissance party, but they could force it to check every door. They turned the track signs around, opened empty sluices and beat out the living code in three different places.
While the guards chose which way to go, the synchronisation finished.
The first batch emerged after seven minutes. Six new sparks rose above the hopper, making seven with Irsa. Marek took six direct lines. Irsa remained the anchor.
The second batch brought the number to thirteen. Marek handed one new form to the external node. The red branch on the casing accepted her without a voice and directed her towards the northern entrance.
By the third cycle, the node was already directing seven sparks and did not require a separate command from Marek for each one. He gave it only the local task: close the breach. The forms then assigned themselves positions along the cracked pipe.
Saya tested the limit with a safe command. She placed three lengths of rail beside it and asked the node to join only two. The seams touched the first pair and left the third length lying where it was, though carrying on would have been easier. Then Dara struck the emergency cut-off. All seven local forms froze, but Marek's twelve direct lines remained. The node did not read the wishes of the people around it, did not expand the task by itself and allowed another hand to stop its part of the network. Only after that test did Saya permit production to continue.
The old stove heat gave rise to a new specialisation. The repair fire's last wish was simple: join what had come apart. The sparks became flat, settled along the edges of the metal and baked the crack shut with a cold red seam.
Marek called them seams.
The fourth batch brought the number to twenty-five. Marek held twelve lines directly, and the external node took the rest. The network was now pulling medicine from the pipe, reinforcing the northern entrance and searching for a route to the pump, all at once.
The Salt Guard reconnaissance party reached the first door. Beran and the workers held the manual bolt in place, but the metal began to buckle. At the same moment, a crack opened in the southern wall. If they sent the seams there, the guards would get in. If they left the wall, water would flood the stove before the next cycle.
This time Marek did not decide everything alone. He left the direct lines at the door and gave the southern wall to the external node. The twenty-four local lines did not require him to watch every movement. For the first time, the choir worked in two places without tearing him apart.
The fifth batch brought the number to thirty-one sparks.
At the forty-second minute, the stove completed its sixth cycle. There was enough ash for five forms. Marek did not thin the material to produce a weak sixth. Five sparks rose above the firebox.
Thirty-six.
Twelve direct lines. Twenty-four local.
The seams closed the southern wall seconds before the water broke through. At the northern entrance, the holders secured the bolt while the listeners guided the workers to a side door. The Salt Guard reconnaissance party entered an empty depot and found only a cooling trace.
Marek led the network out through another tunnel. Thirty-six red-grey lights moved in three streams without hindering one another. For the first time, the people of the Soot saw neither a lone cold spark nor a team of carriers, but a working network.
Yuna counted every form by its flashes. Saya checked the stove and confirmed that they had taken no extra measure of heat and no human memory had been used as fuel.
Only then did Marek allow himself to sit down.
Beran handed him an apple from the emergency rations, and Marek stopped unexpectedly after cutting away the first strip of peel. He knew the smell had once meant something. He even knew the memory was tied to home and Ella.
But he felt nothing.
Saya noticed him staring at the peel.
"What exactly did you give up?"
"What we agreed."
"That isn't an answer."
Salt chimed again in the far tunnel. Marek rose before Saya could ask again.
One of the listeners returned with a map of the pump branch line. It showed a corridor that was too clean and too straight, as though the Guard had forgotten to block the only convenient way out.
Irsa touched the red line of the external node and said in another person's voice:
"The key can be erased."
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