Water fell from the ceiling of the abandoned isolation room.

One drop landed on Mira’s public-broadcast draft and blurred the words risk warning.

The second struck Ian’s cheek.

He wiped it away with the back of his hand and smelled it.

“Don’t drink it,” Mira said.

“I didn’t.”

“Don’t touch your mouth either.”

The stain on the ceiling spread quickly.

There were no water pipes above Abandoned Isolation Sector Four. When the facility had been shut down fourteen years ago, both the supply lines and the culture-fluid lines had been cut. The only thing left was an old ventilation duct leading toward the outer-wall pressure-buffer chamber.

Sarah held a sample container under the stain.

“It could be coolant,” Mira said.

“Coolant would be blue.”

“It could have discolored in an old pipe.”

“There is no pipe above us.”

A third drop fell.

Soon they could no longer count them one by one.

A thin stream formed along a seam in the ceiling. Under the emergency lights, the water looked clear. Sarah tested the conductivity and acidity of the sample.

“pH 5.3. High dissolved-salt content.”

Daniel asked, “Not city water?”

“Standard supply water is neutral.”

Ian looked up.

“Rain?”

No one answered immediately.

In City Seven, rain was something seen in educational recordings. Water that did not emerge from a ceiling nozzle in a measured amount, but fell randomly from the sky. Children had never seen it. Most adults had not either.

Mira opened an old facility diagram mounted on the wall, etched into metal rather than pulled from the central network. The ventilation duct rose thirty-eight meters and met the outer-wall drainage chamber.

“The outer-wall drainage room is overflowing.”

Elias held his remote lock key against the door gap.

City alerts arrived all at once.

EXTERNAL PRECIPITATION DETECTED.

HOURLY PRECIPITATION: UNMEASURABLE.

OUTER-WALL DRAIN GATES 7 AND 8: NO RESPONSE.

LEGACY PHYSICAL-MAINTENANCE PORTS: LOCKED.

Mira closed her eyes.

1,408.

The outer-wall drain gates were among the old service ports sealed after her public confession.

“Is there anyone who can open the drains manually?”

“Twelve outer-wall maintenance workers are under movement restriction,” Elias said.

“Can they reach the drainage room?”

“If they have authority.”

“The authority has been revoked.”

Mira looked up at the ceiling.

“Then the rain goes to the lowest place.”

The abandoned isolation room was the lowest room in the Life Synthesis sector.

Sarah added a reagent to the sample. The clear liquid turned pale brown.

“Organic reaction.”

“How much?”

“At least twenty times the standard city supply. I’d need a microscope to tell whether it’s fungal material or spores.”

Ian rubbed the back of his hand against his work clothes.

Mira caught his hand at once.

“Does it sting?”

“A little.”

Three small red spots had appeared.

Sarah brought over a portable scanner.

“Can I examine it?”

Ian hesitated, then nodded.

Sarah held the optical plate close to his skin without touching it.

“Surface inflammation. I can’t yet tell whether it’s an immune response or chemical irritation.”

“Should I wash it?”

“With city water.”

Less than three hundred milliliters remained in the water pouch. It was also the water meant for Rina’s heat exchanger.

Mira wiped Ian’s hand with the dry part of her sleeve.

“Is that enough?”

“For now.”

The stream from the ceiling thickened.

Cheers came through the copper voice tube.

Someone shouted, “Water!”

“Don’t drink it!” Mira yelled into the tube. “It came in from outside. It tested positive for organic material!”

“We don’t have any water!”

It was Rahim.

“Do you have proof it’s dangerous to drink?”

Sarah answered, “No. We also have no proof it’s safe.”

“What if we boil it?”

Mira pictured the corridor equipment.

“There’s a waste-heat pipe from the culture chambers. If it’s still hot, you can boil water on it.”

“The access plate is locked.”

Every answer came back to the same point.

Legacy ports locked.

Elias sent another command demanding reversal of the closure.

RISK OF REPEATED UNAUTHORIZED SUBJECT EXCHANGE.

“Prioritize the current flood risk.”

ESTIMATED FLOOD FATALITIES: 0–112.ESTIMATED RESOURCE LOSS FROM SUBJECT-EXCHANGE PROPAGATION: UNCALCULABLE.UNCALCULABLE RISK WILL BE AVOIDED FIRST.

Mira almost threw the lock key at the wall, then stopped.

Breaking the device would not change the command. It would only remove one screen on which they could see it.

“What about Abel?” she asked. “He may still have the rules from before the legacy-port lockdown.”

“To reach Abel, we would have to leave the isolation room,” Elias said.

“And he’s farther away than the outer-wall drain room.”

Daniel pointed beneath the culture tank.

“The water’s going there.”

The floor sloped toward Rina’s manual pump. Rainwater had begun collecting under the pump base.

The power lines were temporary copper wiring. If water reached the terminals, they could short.

Mira and Noah spread packaging membrane they had removed from the culture tank across the floor. They tried to redirect the water toward the door, but the membrane was too narrow.

The perimeter guards removed their waterproof outer coats.

Mira overlapped them into a makeshift channel and clipped the edges together with metal fasteners because they had no stitching tools.

The water flowed toward the door.

It passed outside through the finger-wide gap beneath the pressure door.

People in the corridor reached out with containers and bare hands to catch it.

“I told you not to drink it!” Mira shouted.

A man answered, “How long are we supposed to wait?”

“At least until you boil it.”

“Can you open the heat pipe?”

“You’ll have to break the access panel.”

“How?”

Mira reconstructed the corridor in her head.

“On the north wall of the culture room, there’s a vertical seam. Fourth anchor point up from the floor.”

“They all look the same.”

“Hold your hand near them. The warm one is the waste-heat pipe. Don’t touch it directly.”

She heard people feeling along the wall.

Rahim said, “Found it.”

“Hit the corner of the panel. Not the center—the hinge side.”

Metal rang outside.

Mira could still hear in her memory the moment one cooling-facility worker had lost signal before her public broadcast.

“Everybody stand back before you hit it again. There may be steam inside.”

“Got it.”

After three blows, the access panel fell away.

Hot air flooded the corridor strongly enough that even through the voice tube Mira could feel the shift. People cheered.

She explained how to boil the water and improvise a condensation cloth. She repeated several times that the metal cleaning vessel must be placed over the waste-heat pipe without sealing it.

“Do not close the lid. It can explode.”

“We know.”

“Leave it fully open.”

“I said we know.”

The people learned how to keep themselves alive without forgiving Mira.

The two things could exist together.

An alarm sounded from Rina’s tank.

Sarah checked the circulation fluid.

“Her oxygen saturation is rising.”

“Isn’t that good?” Daniel asked.

“The pump output hasn’t changed.”

Rina’s oxygen saturation climbed from eighty-four percent to eighty-nine, then ninety-two.

The black fibers around her neck flashed rapidly.

Their rhythm resembled the rhythm of rain striking the ceiling.

Sarah opened the symbiont-signal readings on the outside of the tank.

“An external biological signal is entering.”

“From the rain?” Mira asked.

“Possibly through the entire ventilation duct.”

There had been no black tissue in this room.

Now, from inside a ceiling seam, a thread of gray matter descended. It was finer than a hair and wet. At the tip, it spread apart in the air and formed a transparent membrane.

Daniel picked up a metal rod.

“Cut it.”

Sarah stopped him.

“Wait.”

“It’s connecting to Rina.”

“Her oxygen saturation just recovered.”

“You don’t even know what it’s doing.”

“That’s why I want to observe it.”

Daniel asked Rina, “Does it hurt?”

Her voice came through the contact stethoscope.

“Cold.”

“Where?”

“Inside.”

“Do you want it gone?”

Rina watched the gray thread.

“I don’t know.”

Daniel said, “If you don’t know, we cut it.”

“You decide?”

He could not lower the metal rod.

Sarah placed a sample dish under the gray thread. The thread spread rapidly when it touched the dish. It wrapped around a drop of water and formed a tiny bubble.

Oxygen.

“Photosynthesis?” Mira asked.

“There isn’t enough light. It seems to be using stored chemical energy.”

“How long can it do that?”

“I don’t know.”

As the bubble grew, black specks rose along the surface of the gray thread.

Sarah covered the sample dish.

“They may be spores.”

One of the guards coughed.

Once at first.

Then repeatedly. He put his face shield back on, but the internal display was dead and could not show filter status.

Noah led him toward the door.

“My eyes sting.”

Red blotches appeared around the guard’s neck.

Sarah checked the allergy suppressant she still had.

“One dose.”

“Give it to him,” Noah said.

“It could still be mild.”

“If we wait until it worsens, we may be too late.”

The guard shook his head.

“Check the people outside first.”

Coughing came through the copper tube.

Not one person.

People who had collected the rainwater were beginning to report pain in their eyes and throats. Those who had inhaled steam while boiling it developed symptoms faster.

Sarah spoke into the tube.

“Anyone having trouble breathing?”

Three people answered.

Rahim said, “Kerin collapsed again.”

“Not low blood sugar? Breathing?”

“She’s holding her throat.”

Sarah looked at the injector.

The guard inside.

Kerin outside.

One dose.

“Send it out,” the guard said.

Noah looked at him.

“You may get worse too.”

“My suit filter is still attached.”

“We can’t verify that. The indicator is dead.”

“I can still breathe.”

Sarah put the injector through the sample-transfer tube.

“Place it against the outside of her neck and press. Don’t try to find a vein.”

Rahim took it.

A few seconds later, Kerin’s breathing slowed slightly.

The guard sat against the wall. Tears kept streaming from his eyes, but his breathing remained stable.

“Boiling may reduce microorganisms,” Sarah said, “but proteins or toxins can carry with the steam.”

“Then how do we filter it?” Mira asked.

“With our current equipment, I cannot guarantee safety.”

“Not guarantee. Possibility.”

Sarah looked at the gray-thread sample.

“Heat denaturation, then activated carbon, if we have any, might absorb some compounds.”

“There’s activated carbon in the air filters.”

Noah removed the filter from the coughing guard’s face shield.

“If we use this, the protective mask will no longer function.”

The guard said, “Its display is already dead.”

“Display and filtration are separate.”

Mira took the filter.

“How many people can this serve?”

“We don’t know what is in the water. I can’t calculate that.”

“Can we make another one?”

The guards looked at one another.

Elias removed the filter from his emergency respirator.

“Two.”

Noah removed his own face-shield filter.

The others followed.

Seven filters.

Mira did not cut them open. Without knowing the internal layer structure, opening them might mix activated carbon with fiber membranes. The entire filters had to be connected in series through a water line.

They cut an unused old culture-fluid tube and made it into a filtration pipe. Noah held the joints while Sarah tested for leaks with soap film. Mira aligned the filter flow directions.

The people outside could not build the same assembly.

They pushed the whole filter pipe through the gap under the door.

“Run the water through this slowly.”

Rahim took it.

“What about you?”

“We still have water.”

Daniel looked at the remaining pouch.

Mira saw the look and did not change her words.

The filtered rainwater came out clear. The smell was weaker too.

Sarah still did not call it safe.

Outside, they gave Kerin one sip first.

When ten minutes passed without new symptoms, they shared small amounts with the pregnant technician and people who had children. No one drank enough.

The rain kept coming.

More water was falling from the ceiling than they could send through the channel under the door. The level rose above their ankles.

The pump terminals sat above a temporary waterproof membrane, but they would not stay dry for long.

Mira looked at the facility diagram again.

There was an emergency drain in the floor. It led in the opposite direction from the outer-wall buffer chamber, down toward an old wastewater reservoir beneath the city.

If they opened it, the room would drain.

If the pressure in the lower reservoir was high, contaminated material could flow backward.

There were no central sensor readings.

“We have to open the drain.”

“We don’t know the state of the lower reservoir,” Sarah said.

“If we don’t open it, the pump goes under.”

Daniel looked at Rina.

“Open it.”

Mira found the round drain cover. In its center was a legacy physical-maintenance authentication unit.

Red lock indicator.

One of the 1,408.

Noah inserted a screwdriver. The blade bent.

“Three locking pins.”

Mira felt along the edge of the cover. It was not completely sealed. Beside it was a thin rupture membrane designed to open slightly if a pressure differential developed.

“If we can’t open it from above, we make something push from below.”

“How?”

Mira looked at the pump’s reserve pressure line.

It was not connected to Rina’s circulation. It was a compressed-air cleaning line for the isolation room.

“Pressurize it and break the membrane.”

Sarah said, “If pressure enters the wastewater reservoir, gas from inside may flow back.”

“That’s why everyone moves toward the door.”

“Rina can’t move.”

“Seal the tank intake.”

Rina spoke.

“Again because of me?”

Mira went close to the glass.

“It isn’t only your pump. The whole room’s power is going underwater.”

“What if we send the water outside?”

“The corridor is already flooding too.”

“If we open the drain, what’s below?”

Mira could not answer.

She did not know whether anything lived in the wastewater reservoir. She did not know whether people were there.

“I don’t know.”

Rina closed her eyes.

“There’s no place that’s nowhere.”

Mira held on to the sentence.

“No,” she said.

“Water always arrives somewhere.”

Elias asked, “What is the alternative?”

“Cut power and move the culture tank to higher ground.”

“Rina’s survival time?”

Sarah said, “The current symbiotic tissue is producing external oxygen, so it may be longer than before. We cannot measure it.”

“And if we open the drain?”

“We also cannot measure the toxicity of any backflow.”

Neither option could be calculated.

Elias looked at Mira.

“Your judgment?”

“Open the drain.”

“Basis?”

“If we shut the power off, the pump definitely stops. Backflow might happen. Or it might not.”

“Rina,” Daniel said. “You heard that?”

“Yeah.”

“Open it?”

“Is there no one below?”

Elias checked an old population map.

“No official residents.”

“You added official,” Mira said.

“There is no record of unofficial residents in the wastewater reservoir.”

“There are no sensors either.”

Rina placed a finger against the vibration membrane of the contact stethoscope.

“Open it.”

“You sure?” Daniel asked.

“No,” Rina said.

“Open it anyway.”

Mira connected the compressed-air line to the rupture-membrane port.

Everyone moved toward the door. The guards held waterproof sheets in front of the culture tank.

Mira worked the manual compressor handle.

Once.

The pressure gauge did not move.

Twice.

The needle reached 0.2.

On the third stroke, a low resonance came from beneath the floor.

Ian covered his ears.

“There’s a sound down there.”

“Water?”

“No.”

“What is it?”

“Scratching.”

Mira stopped pumping.

Everyone listened.

Something beneath the floor was scratching at the round drain cover.

Once.

Twice.

The intervals were not those of a human hand knocking.

Sarah held a scanner near the floor.

“Biological vibration.”

Daniel asked, “Something’s alive down there?”

“That I don’t know.”

The water rose above their ankles.

The waterproof membrane beneath the pump terminals began to float.

Mira gripped the compressor handle.

“We have to keep going.”

“Wait,” Ian said.

He went closer to the drain.

“Don’t,” Mira said, but she did not grab him.

Ian crouched without putting his knees into the water. Instead of his curled right fingers, he placed his left palm on the cover.

No blue lines lit beneath his skin.

“What does it sound like?” Rina asked.

“Not words.”

“Then what?”

“It wants to come up.”

“If we open it, does the water go down?”

“Yeah.”

“And it comes up too?”

Ian nodded.

Rina said, “Open it.”

Mira pressed the compressor.

Pressure 0.4.

0.7.

The rupture membrane broke.

The circular cover lifted by the width of one finger joint.

Black air did not come out first.

Water rushed downward.

A violent whirlpool formed, pulling at the hems of their clothes.

Mira and Noah dragged Ian back.

The water level dropped quickly.

Then a single white stalk rose through the drain gap.

No eyes. No leaves.

A stem jointed like something wet and articulated.

Its tip opened and drew in the air of the isolation room. Tiny pores across its surface opened and closed.

Sarah started toward it. Mira stopped her.

“Measure first.”

Sarah raised an air monitor.

Oxygen concentration increased by 0.3 percent.

At the same time, an unknown-spore alarm appeared.

The white stalk followed the draining water upward.

One became two.

Two became six.

The black fibers inside Rina’s culture tank contracted in the same rhythm.

Rina said, “I know that.”

Daniel put his hand on the glass.

“Where have you seen it?”

“I haven’t.”

“Then how do you know it?”

Rina’s eyes followed the white stalks.

“My lungs do that.”

A new city alert appeared.

EXTERNAL PRECIPITATION ENTRY POINTS: 46.

UNIDENTIFIED BIOLOGICAL RESPONSE: 19 SECTORS.

REVERSE-DIRECTION GROWTH DETECTED THROUGH LEGACY DRAINAGE NETWORK.

The rain had brought more than water into the city.

It had opened a path for the things that had been waiting below.