Exchange Conditions

The countdown to the channel opening had begun. Su Wan from Line A announced the specific plan to Lin Shen: the temporary channel could only last thirty minutes, and the energy was only enough to transmit one person. Lin Shen had to stay here, taking the place of the projected version of Su Wan, to maintain the conservation of mass between the two worlds. Lin Shen agreed. But three hours before the countdown hit zero, a monitor rushed into the control room—someone of unknown identity had crossed through the channel.

On the morning of the third day, the atmosphere in the research institute was completely different from the first two.

The lights in the hallway had been on all night. Su Wan from Line A's office was piled high with printed data sheets and hand-drawn energy field simulation diagrams. The cup of milk tea on her desk had gone from hot to cold, and from cold to developing tea stains. She had barely slept in two days, her eyes bloodshot, but her hands moved with startling steadiness—adjusting parameters, calibrating curves, verifying energy equations—like a machine that never made mistakes.

"I've already calibrated the basic framework of the channel at the bottom layer," she said, slapping the last sheet of calculation paper onto the whiteboard and securing it with a magnet. "Now let me explain the specific plan. Both of you listen carefully."

Two Lin Shens sat across from her. One in light gray, one in dark blue. Like a man and his shadow, sitting in two seats that branched off from the same timeline.

Su Wan from Line A turned on the projector. A three-dimensional energy field model appeared on the screen—two parallel curves with a red intersection point in the middle.

"The underlying logic of the Mirror Project is this—there is an energy interlayer between the membranes of the two parallel worlds, what you call the 'crevice.' Under normal circumstances, the membranes are sealed, and no matter can pass through." She pointed at the red dot. "The accident two years ago tore a tiny crack here. The correction mechanism has been repairing it, but it hasn't fully healed yet. We can use this semi-healed crack, forcing it open with a定向 energy pulse to create a temporary channel—about two meters in diameter, lasting thirty minutes."

"Thirty minutes," Lin Shen from Line A repeated. "Enough to send one person?"

"Enough. But only one person." Su Wan from Line A's laser pointer stopped at Point A on the model. "Lin Shen from the original line enters here—the hydroelectric plant's transmission pod in Line A. Cross through the crevice, find the projected Su Wan inside it, then together cross to Point B—the control room of the hydroelectric plant in your world."

"And who maintains that?" Lin Shen from the original line asked.

"Each endpoint needs one person." Su Wan from Line A wrote "Lin Shen from Line A" next to Point A and "Jiang Fei" next to Point B. "Lin Shen from Line A maintains the energy output in the transmission pod control room. Jiang Fei maintains the receiving field at the receiving end in your world. The energy at both ends must be synchronized—the margin of error cannot exceed 0.3 fluctuation units. If either end drops the ball—"

"The channel will collapse before the transmission is complete," Lin Shen from Line A finished for her.

"Correct. The consequence of channel collapse—the person in transit will be trapped in the crevice forever. Whether it's the one going or the one being brought back."

Lin Shen from the original line tapped his knee unconsciously three times with his fingers.

"There's another problem," Su Wan from Line A said, pulling the laser pointer back from Point B and stopping at Line A. "You can go, she can come back—but what happens after? Your world will have one extra Su Wan. The correction mechanism will be triggered again. Unless—"

"Unless someone stays," Lin Shen from the original line said.

"Correct." Su Wan from Line A turned off the projector and turned to face him. "One Lin Shen goes, one Su Wan comes back. Conservation of mass—the scales of the two worlds are still balanced. The correction mechanism has no reason to trigger again. You stay, taking the place of the projected Su Wan. Fill the void she leaves behind with your existence."

The only sound in the conference room was the hum of the fluorescent lights.

"You stay here," Su Wan from Line A said, her voice a little lower than before. "I'll help you rebuild everything. Identity, career, social connections—you have Lin Shen from Line A's fingerprints and DNA. The system won't detect any difference. You can start over anywhere. You can see Su Wan here—every day."

She paused.

"I know I'm not her. But I also want to help you."

Lin Shen from the original line looked at her. When he had first seen this Su Wan two days ago, all he could think was "this isn't my Su Wan." But it was different now. She was another person—with her own sharpness, her own prudence, her own projector and data sheets. She was like two paintings by the same artist with different color schemes: the original line Su Wan was watercolor—soft and translucent; Su Wan from Line A was oil paint—thick and textured.

But their foundation was the same—both willing to sacrifice themselves for the ones they loved.

"I agree," Lin Shen from the original line said, his voice very soft. "As long as she can go back alive, I'll do anything."

Su Wan from Line A didn't answer immediately. She lowered her head, took off her glasses, and wiped the lenses with her sleeve. After putting them back on, she turned around and wrote a set of numbers on the whiteboard.

"Channel opening countdown—three hours."

The next three hours were the quietest three hours in the entire research institute.

Su Wan from Line A sat in front of the control console, her ten fingers flying across the keyboard, new data refreshing on the screen continuously. Lin Shen from Line A sat in a corner, one leg crossed over the other, an old worn-out notebook spread open on his knee—it was the diary he had written when he first arrived in Line A. The first page had only one sentence: "Standing on the street of a strange world, everyone has a photo they can look back at, but I don't."

He closed the notebook and stood up.

"I'm going to get some coffee," he said. "Do you need some?"

Lin Shen from the original line shook his head.

Lin Shen from Line A walked out, the door closing behind him.

Only Lin Shen from the original line and Su Wan from Line A remained in the conference room. The keyboard sounds stopped.

"The things he's said in the past two days," Su Wan from Line A said, not turning around, still staring at the screen, "are the most he's spoken since he came here."

"He doesn't talk much normally?"

"He does. But rarely about what he's thinking. For the first half year after he came, he barely spoke. Every morning he'd get up, make breakfast, go to work, come back and help me collect data—not a word more than necessary. I thought he was just unsociable. Then one day in the middle of the night, I woke up and he wasn't there—he was sitting alone in the living room, facing the balcony. I asked him what he was looking at. He said: 'The moon. The moon here is offset by about three degrees from where it was over there.'"

Su Wan from Line A's fingers stopped typing.

"That was when I knew. He wasn't unsociable. He was reminding himself every single day—this isn't his home. And his home, he can never go back to."

Lin Shen from the original line said nothing. He knew why Lin Shen from Line A didn't talk much. Because he was the same—if tomorrow he were locked in a strange world, he too would wake up in the middle of the night every day to see how many degrees the moon was off.

"That's why he's helping you," Su Wan from Line A turned around and looked at Lin Shen from the original line. "Because you are his only way home. Not back to the original world—he has no original world to return to—but back to himself."

A short alarm suddenly sounded from the console.

Su Wan from Line A immediately turned back to the screen. A red warning box popped up on the display, with a set of data fluctuating rapidly.

"What's wrong?" Lin Shen from the original line stood up.

"Energy fluctuation. Not from our side—" Su Wan from Line A zoomed in on the data, her brows furrowed. "It's the other end of the channel. Someone is crossing through the channel. It's not a normal startup from the transmission pod—it's a Force Crossing. Someone is forcibly breaking through the crack."

"Lu Yan."

Su Wan from Line A's fingers flew across the keyboard. The data stream on the screen cascaded down like a waterfall.

"He's in your transmission pod—no, he's already crossed. He's passed through the crack and is heading toward Line A. No—" She paused, enlarging another set of data. "More than one person. His advance team has also crossed. At his current speed—"

The door was suddenly pushed open. Lin Shen from Line A stood at the entrance, holding two cups of coffee in his hands, the coffee sloshing inside the cups.

"Someone of unknown identity has crossed through the channel and entered," he said. "About ten minutes ago. The perimeter alarm for the entire institute has gone off."

"I know." Su Wan from Line A stood up and turned the screen toward him. "Lu Yan has come through with the Correctors. How did they know the channel would open again—" She paused, her face changing color. "Last time during the transmission, they might have left a tracking device near the pod. Jiang Fei might have—"

"Jiang Fei is fine," Lin Shen from Line A said, setting the coffee down on the table with steady hands. "At least for now. The tracking device must have been planted by Lu Yan before their last crossing. He's been waiting for this moment—waiting for the channel to open again."

New data jumped onto the screen. The frequency of the energy fluctuations was accelerating, exceeding the limit the crack between the two lines could withstand.

"How many people do they have?" Lin Shen from the original line asked.

"About thirty in the advance team. Lu Yan is leading them personally." Su Wan from Line A stared at the screen. "Their target isn't us. It's the hydroelectric plant—Line A's hydroelectric plant. They're going to blow up the transmission pod." She turned sharply to Lin Shen from the original line. "Lu Yan wants to destroy the transmission equipment before the channel opens. That way, your Su Wan will never come back."

The air in the conference room froze for a few seconds.

"Does the hydroelectric plant have defenses?" Lin Shen from Line A asked.

"No. That plant has been abandoned for ten years. No security at all."

"Then we go," Lin Shen from the original line said, already standing up, reaching for his jacket on the back of the chair. "Right now. Get to the hydroelectric plant before Lu Yan does, and hold the transmission pod."

"The countdown is still two and a half hours." Su Wan from Line A glanced at the screen. "Lu Yan is faster than us—he's using a Force Channel, bypassing the calibration steps to cross directly. At his current rate, he'll reach the Line A hydroelectric plant in about an hour."

Lin Shen from Line A picked up the coffee from the table and took a sip. It was no longer hot. He downed it in one go and slammed the cup back onto the table.

"I'll drive. You two keep monitoring the data." He glanced at Lin Shen from the original line. "You'll be going into the transmission pod soon. Save your strength."

"How's your driving?"

Lin Shen from Line A smiled. "As good as yours."

Su Wan from Line A had already started packing her equipment. She stuffed her laptop into her backpack, grabbed a handful of data cables, then pulled a small black box out of the drawer and handed it to Lin Shen from the original line.

"Emergency Beacon. If the channel becomes unstable during transmission, it will automatically emit a pulse—enough to buy you a few extra seconds."

"Who was it originally meant for?"

Su Wan from Line A didn't answer. She pressed the black box into his hand.

"Let's go."

The three of them rushed out of the conference room. The alarm lights in the hallway were already fully on, red light sweeping across the white walls again and again. Other researchers at the institute were evacuating. Someone ran over holding files and shouted "Professor Su," but she waved them away.

In the parking lot, Lin Shen from Line A got into the driver's seat, Su Wan from Line A sat in the passenger seat adjusting the data, and Lin Shen from the original line sat in the back. As the car shot forward, the tires screeched against the pavement.

"From here to the hydroelectric plant," Lin Shen from Line A glanced at the navigation, "thirty-seven minutes. Lu Yan has about fifty minutes."

"That's enough," Lin Shen from the original line said.

"Enough," Lin Shen from Line A repeated, stepping on the accelerator. "But do you know why Lu Yan is so hell-bent on destroying the channel? It's not just to stop you."

"I know." Lin Shen from the original line watched the streets racing backward outside the window. "His wife died in the crevice. He won't allow anyone a second chance—because he didn't get one himself."

Su Wan from Line A turned her head from the passenger seat and looked at Lin Shen from the original line. In that split-second glance, something seemed to shift.

The car sped onto the highway. In three hours, the channel would open.

And now, Lu Yan was crossing through the rift, heading toward them.

Outside the window, the city of Line A blurred past. Unfamiliar logos on billboards, month names on street signs that he didn't recognize—all of this should have belonged to the world of Lin Shen from Line A and Su Wan from Line A, but now it had become the prelude to a decisive battle.

Lin Shen from the original line gripped the black box in his pocket, his knuckles turning white.

Two and a half hours left.