Forty-three seconds after the trackers began cutting through the door, the air in the maintenance passage changed.

The dry, mechanically purified air took on the smell of old metal. There were no recent inspection marks on the walls. Gray powder coated the floor, preserving every footprint Mira and Ian left behind.

City Seven cleaned even unused spaces on a regular schedule.

Dust meant they had crossed beyond Continuum's managed territory.

Mira could not decide whether that should make her feel relieved or afraid.

Behind them, the cutter scraped against metal.

Ian asked, "Where are we?"

"An old education-network maintenance passage."

"Where does it go?"

Mira did not answer.

The truth was, she did not know.

On current city plans, this passage had been marked closed forty-eight years ago. She had seen the pre-closure plans only once, when she was an apprentice maintenance technician.

Her instructor had said then:

Don't memorize roads that no longer exist. The city keeps changing.

Mira had never believed that.

Even when machines built new routes, old ones remained as matter. Pipes stayed buried inside walls. Severed wires hung where they had been cut. The spaces behind locked doors did not vanish.

The city could forget.

Matter remained.

And that was what was keeping them alive now.

"Mom."

"Walk quietly."

"You said before that you could switch me with another kid."

Mira quickened her pace.

"The record only said it might be possible."

"Are you going to do it?"

"No."

The answer came too quickly.

Ian did not ask again.

His silence followed her down the passage.

The corridor split in two.

A rusted sign hung on the right.

FUNCTION ASSIGNMENT REGIONAL RELAY 7-B

The sign on the left read WASTE HEAT RECOVERY FACILITY.

Mira turned right.

Ian read the sign.

"Function assignment?"

"An old relay."

"Why are we going there?"

"To see if I can put your record back the way it was."

"The way it was?"

"Before it became zero."

"Without putting another kid in?"

Mira stopped for a moment.

"That's the first thing I'm going to look for."

The cutting noise behind them stopped.

The door was open.

A moment later, footsteps sounded from the passage behind them at regular intervals.

The people were not running.

They moved as if they already knew exactly where Mira was going.

Mira grabbed Ian's hand and ran.

The entrance to the old relay room was sealed by a manual pressure door. When Mira turned the handle, hardened sealant tore somewhere inside.

The door opened two finger-widths and stopped.

Mira shoved her shoulder into it.

It did not move.

A pressure-difference warning plate was fixed beside the frame. The relay room's internal pressure was lower than the corridor's. Force the door open, and outside air would rush in, potentially triggering the automatic closure mechanism.

"Get back."

Mira pulled out the tools she still had.

"Are you breaking this one too?"

"I'm opening it."

"That's the same thing."

Mira wedged a pry bar into the gap.

A red glow appeared around the bend behind them.

Searchlights.

The retrieval agents were close.

"Ian, grab the handle."

"How?"

"When I push, turn it counterclockwise."

"It won't move."

"Keep turning until it does."

Mira threw her weight against the pry bar.

The metal bent.

The pressure door opened a little farther.

A voice came from the passage behind them.

SUBJECT: IAN HAN.REMAIN AT YOUR CURRENT LOCATION.NO HARM WILL COME TO THE GUARDIAN.

Ian's grip weakened.

"Mom, they said they won't hurt you."

"Turn the handle."

"If we go with them, maybe they'll explain."

"If they meant to explain anything, they would've done it already."

GUARDIAN: MIRA HAN.INTERFERENCE WITH SUBJECT MOVEMENT MAY RESULT IN SUSPENSION OF GUARDIAN FUNCTION.

"They're threatening to suspend my function," Mira said.

"But notice how they didn't say they wouldn't hurt me."

The searchlights drew closer.

Mira shoved the pry bar again.

The inner seal tore free.

Air screamed into the room with a high whistle.

"Now!"

Ian turned the handle.

The door opened.

They slipped inside and forced the handle back the other way.

Just before the door closed, one of the retrieval agents came around the corner.

Gray protective suit.

Opaque face shield.

In his hand was not a weapon, but a short medical injector.

He ran toward them.

Mira slammed the door.

The injector thrust through the gap, aimed at Ian's arm.

Mira struck it down with a tool.

Clear fluid spilled across the floor.

The agent's hand became trapped between the doors. His protective glove tore.

Blood appeared.

Mira pushed harder.

For the first time, the agent groaned.

Ian shouted.

"Mom, his hand!"

Mira did not stop.

The door closed completely.

Something fell to the floor outside.

Mira locked the handle.

Ian stared at the door.

"You hurt his hand."

"He's alive."

"How do you know?"

"He screamed."

"Even though he got hurt?"

"If they catch us, you might get hurt too."

"We don't know that yet."

Mira turned to him.

For the first time, she wondered what she looked like through her son's eyes.

Until a short while ago, she had been someone who repaired the city's air.

Now she was someone who had watched a man's hand trapped in a door and kept pushing.

"I'm sorry," Mira said.

Ian did not answer.

The relay room was larger than she had expected.

Old computation terminals lined the walls. A cylindrical memory unit stood in the center. Cables hanging from the ceiling reached the floor like dead, dried roots.

The power had been disconnected.

Mira opened the emergency power cabinet.

The storage cells had been removed long ago, but the terminals for an external power line remained.

She pulled the battery from her work key and attached the leads.

"If you use that, won't your work key stop working?" Ian asked.

"It'll work for a little while."

"How long is 'a little while' when you say it?"

"As long as I need."

Current flowed.

One of the old terminals came to life.

A single number appeared in the center of the screen.

0

A moment later, it changed to 1.

The numbers continued rising at a steady pace.

Mira's hand stopped.

"Look at this."

Ian stepped closer to the screen.

"It keeps adding one."

"It's the relay's startup test."

"Zero, then one."

"It's just checking numbers."

That was what Mira said.

But she could not look away.

Yesterday, inside the purification system, she had seen 9.3 billion recovery commands.

Today, an abandoned function-assignment relay had started at zero and was steadily adding one.

When startup finished, the numbers disappeared.

REGIONAL FUNCTION ASSIGNMENT RELAY 7-BLAST SYNCHRONIZATION: 48 YEARS, 3 MONTHS AGOCENTRAL CONNECTION: UNAVAILABLEPHYSICAL ADMINISTRATION MODE: PERMITTED

Mira inserted the authentication component into the slot beneath the terminal.

SENIOR FUNCTION-ASSIGNMENT AUTHORITY VERIFIED.

Ian looked at it.

"That's the thing you took earlier?"

"Yeah."

"Did you steal it?"

"I ripped it out."

"Is that worse?"

"Doesn't matter right now."

Mira called up the subject records.

Ian's name appeared at the top.

IAN HANTEMPORARY FUNCTION CODE: 0STATUS: AWAITING RETRIEVALSCHEDULED TIME: 11:31:04

Three options appeared beneath it in red.

RESTORE ORIGINAL ASSIGNMENTEXCHANGE SUBJECT IDENTIFIERLOCAL RETRIEVAL DEFERRAL

Mira selected Restore Original Assignment first.

NO ORIGINAL ASSIGNMENT RECORD EXISTS.

"Why?" Ian asked.

"Maybe you were zero from the beginning."

"Then I never had a function?"

"You hadn't been assigned one yet."

"Other kids aren't zero before assignment."

Mira selected Local Retrieval Deferral.

ENTER REASON FOR DEFERRAL.

She typed: Function assignment error.

NO OBJECTIVE ERROR CONFIRMED.

Guardian objection.

GUARDIAN IS NOT AN AUTHORIZED DEFERRAL PARTY.

Subject health abnormality.

SUBJECT BIOMETRICS NORMAL.

Facility inaccessible.

AUTOMATED TRANSPORT MAY BE ASSIGNED.

Transition procedure dangerous.

The screen paused.

RISK IS NOT A VALID REASON FOR DEFERRAL.

Mira read the sentence again.

Risk is not a valid reason for deferral.

To the system, danger was not a reason to stop.

It was only another variable to include in the calculation.

Someone knocked on the door outside.

Three times.

Evenly spaced.

Ian raised his head.

"It sounds like the thing I heard in the wall."

Then a human voice followed.

"Mira Han."

It was the voice of the retrieval agent whose face had been hidden behind the shield.

"Open the door. The injured person requires treatment."

Mira looked toward it.

"Treat him after you leave."

"If you surrender the subject, neither guardian nor subject will be punished."

"What was in that injector?"

"A sedative."

"For an eleven-year-old, without even checking the dose?"

"The dosage is automatically calibrated to the subject's biometric data."

Ian spoke softly.

"His hand was bleeding."

Mira turned back to the screen.

The final option.

Exchange Subject Identifier.

She selected it.

A warning appeared.

SUBJECT IDENTIFIER EXCHANGE IS PERMITTED ONLY WITHIN THE TRANSITION SUBJECT GROUP.CANDIDATE MUST BE IN THE SAME REGION, OF SIMILAR AGE, AND HAVE COMPLETED A FUNCTION ASSESSMENT WITHIN THE PAST 72 HOURS.EXCHANGE CHANGES THE ADMINISTRATIVE IDENTIFIER OF THE RETRIEVAL ORDER.BIOMETRIC COMPATIBILITY IS NOT ALTERED.THE ORIGINAL SUBJECT'S RETRIEVAL ORDER MAY BE RESTORED AFTER REVERIFICATION.

Ian read the lines aloud.

"Only the administrative identifier changes."

Mira said nothing.

"So if another kid gets taken instead of me, they might still come back for me later?"

"It means they might."

"Then why do it?"

"It can buy us time."

"How much?"

An estimate appeared at the bottom of the display.

ESTIMATED DEFERRAL:MINIMUM 47 MINUTES / MAXIMUM 29 HOURSPREDICTION CONFIDENCE: 31.2 PERCENT

"They don't know."

"No."

"But they'll come for the other kid right away?"

Mira did not open the candidate search.

The voice came through the door again.

"The injured party continues to bleed."

"You're medical personnel," Mira called back.

"Treat him yourself."

"The protective suit has been breached. Infection is possible. The hygiene grade of this sector is unverified."

"That's not my problem."

The instant she said it, Mira heard herself.

Ian heard it.

The man outside heard it.

There was a brief silence.

"Understood," the agent said.

"Then we will begin forced entry."

Equipment activated outside.

The center of the pressure door began to glow with heat.

Mira opened the candidate search.

Seven names appeared.

Every one of them belonged to a child between ten and twelve years old.

The first candidate was from another education district. Their most recent assessment had been seventy-one hours earlier.

ELIGIBILITY CONDITIONS MET.

The second candidate was hospitalized in the medical sector.

The third had one status note:

NO GUARDIAN.

Mira's finger stopped above the name.

A child with no guardian.

There was a good chance no one would notice immediately.

Ian asked, "Who is that?"

"I don't know."

"Is it okay if you don't know them?"

Mira pulled her hand away.

She was ashamed that the name of a child she did not know had seemed easier.

As if guilt shrank when the face was missing.

She searched for another way.

She entered records of the dead.

ONLY BIOLOGICALLY ACTIVE SUBJECTS MAY BE EXCHANGED.

She entered an adult record.

AGE REQUIREMENT NOT MET.

She entered her own identification number.

SUBJECT GROUP MISMATCH.

The system demanded a living child.

The time on the screen continued falling.

11:22:17

The metal at the center of the door glowed red.

Ian said, "Let's go out."

"Where?"

"To those people."

Mira looked up.

"No."

"It's better than sending another kid."

"We don't know what they'll do to you."

"We don't know what they'll do to the other kid either."

"Ian."

"Is it okay because you don't know what happens to them?"

Mira shoved the chair back and stood.

"I didn't say it was okay."

"Then don't do it."

"I don't want to."

"Then why are you still looking?"

Mira could not answer.

A new communication request appeared on the terminal.

SENDER: DANIEL SEO.

Mira stared at it.

She rejected the call.

Another request came.

The third was marked URGENT.

Mira accepted.

Daniel's face appeared.

The corridor of Education Sector 2 was visible behind him.

"Mira, where are you?"

"Why?"

"The school is in chaos because of Ian. Retrieval agents are everywhere."

"Where's Rina?"

"She's being tested."

Daniel looked uneasy, but forced a smile.

"I guess her preliminary results were good. They told her to take a special aptitude assessment right away."

Mira's eyes moved to the candidate list.

The seventh name.

RINA SEO.

MOST RECENT FUNCTION ASSESSMENT COMPLETED: 1 HOUR, 18 MINUTES AGOAGE: 11 YEARS, 2 MONTHSSAME EDUCATION DISTRICTIDENTIFIER EXCHANGE COMPATIBILITY: 98.7 PERCENT

Mira minimized the list.

"Where is Rina right now?"

"School assessment room. But something's strange. They're saying they don't need guardian consent."

"Take her home."

"Why?"

"Just take her."

"The test isn't even finished."

"Daniel. Right now."

His expression changed.

"You know something?"

"Ian had similar tests."

"So?"

Mira heard the sound of the door melting behind her.

"Stop the test."

"Tell me why."

"There's no time."

"That's not yours to decide. This is my daughter."

Daniel glanced off-screen.

"The evaluator just came out."

Mira stopped breathing.

"Where's Rina?"

"They said they're finishing up inside."

"Go in."

"I don't have access."

"Open the door."

Daniel gave a disbelieving laugh.

"Like you?"

"Yes."

"Mira, what the hell is going on?"

She could not tell him.

Daniel leaned closer to the screen.

"Can you check Rina's record? You're maintenance. You can see more than a normal terminal, right?"

"No."

"Just once. If I can know her function in advance—"

"Daniel."

"You know she wants to be an educator. If they assigned her something else, I want time to talk to her before—"

He transmitted his personal identification information.

RINA SEOGUARDIAN AUTHORIZATION REFERENCE: 7-22-4419

The empty field in the exchange window activated automatically.

Mira pulled her hand away from the screen.

Ian had seen the number too.

"Mom."

Mira spoke to Daniel.

"Take Rina and go home."

"As soon as the test is over."

"Now."

"Why do you keep saying that?"

A small hole burned through the center of the door.

Red searchlight spilled inside.

Ian stepped backward.

Mira ended the call.

She selected Rina's name from the candidate list.

The screen asked:

ORIGINAL SUBJECT: IAN HANEXCHANGE SUBJECT: RINA SEOEXCHANGE ADMINISTRATIVE IDENTIFIERS?

"Don't."

Ian's voice.

Mira rested her finger above Confirm.

"We're only buying time."

"Whose time?"

"Time to get you out of here and find a way to save both of you."

"You said before you didn't know how."

"I'll find one."

"What if you can't?"

Mira did not look at him.

The agent outside spoke.

"Forced entry in thirty seconds."

Ian grabbed Mira's wrist.

"Don't do it because of me."

"It's not because of you."

"Then who is it for?"

"I'm your mother."

"That's the reason?"

"That's enough."

Mira pressed Confirm.

The screen did not change immediately.

REVIEW THE CONSEQUENCES OF EXCHANGE.

1. AN IMMEDIATE RETRIEVAL ORDER MAY BE ISSUED FOR THE EXCHANGE SUBJECT.2. THE ORIGINAL SUBJECT'S BIOMETRIC DESIGNATION WILL REMAIN ACTIVE.3. BOTH SUBJECTS MAY BE RETRIEVED FOLLOWING REVERIFICATION.4. THE PERSON EXECUTING THE EXCHANGE ASSUMES ADMINISTRATIVE RESPONSIBILITY FOR THE OUTCOME.

Mira did not read the fourth sentence.

No.

She read it.

She simply decided not to remember it.

FINAL PHYSICAL CONFIRMATION REQUIRED.

From the lower-right side of the terminal, an old metal handle slid outward.

A small red handle.

Its shape resembled the final shutdown mechanism said to exist at the city's center.

Mira gripped it.

Ian released her wrist.

"Mom."

Mira pulled the handle down.

Every screen in the relay room went dark.

One second later, they came back on.

The countdown beside Ian's name was gone.

SUBJECT EXCHANGE PROCESSING.

The cutting outside stopped too.

One retrieval agent said,

"Subject identification data has changed."

Another voice answered,

"Move to the new location."

The footsteps receded.

Mira exhaled.

Ian did not move.

A new message appeared on the terminal.

ORIGINAL SUBJECT: IAN HANRETRIEVAL ORDER: ON HOLDBIOMETRIC REVERIFICATION: IN PROGRESS

Below it appeared another name.

EXCHANGE SUBJECT: RINA SEORETRIEVAL ORDER: ISSUEDESTIMATED ARRIVAL: 00:16:38

Sixteen minutes.

Mira pressed Restore.

EXCHANGE CANNOT BE RESTORED WHILE PROCESSING.

She pressed it again.

The same sentence appeared.

The communicator sounded.

Daniel.

Mira did not answer.

A voice message began playing automatically.

"Mira, something's wrong."

Daniel's breathing was rough.

"The assessment-room door just locked. People in gray suits showed up. They say they're taking Rina somewhere else."

A child's voice sounded in the background.

"Dad?"

Rina.

"Dad, aren't we going home?"

Daniel shouted at someone.

"Where are you taking her? I'm her guardian. Answer me!"

A mechanical voice replied.

SUBJECT: RINA SEO.TRANSFER FOR TRANSITION PROCEDURE.

The message ended.

Ian did not look at Mira.

"Bought some time."

His voice was quiet.

Mira could not say anything.

One final sentence appeared on the screen.

SUBJECT EXCHANGE APPROVED.