An Uninvited Guest: "Nightingale"

Lin Xiao stared at the pale blue waveform on the screen, his fingers lightly tapping the edge of the desk. Every tap carried a steady rhythm, as if he were calculating something. Night had fully fallen outside, and the base's searchlight beams swept across the darkness, occasionally illuminating the barbed wire atop the distant walls and reflecting a cold metallic gleam. Wolf was still adjusting the surveillance parameters, trying to capture more packet signatures. Su Ying walked to the window, lifted a corner of the blinds, and looked into the darkness sliced apart by the lights. "Every two hours and seventeen minutes," she said softly. "Regular as a heartbeat." Lin Xiao did not answer. His gaze fell on the timestamp in the corner of the screen—the next packet transmission was in thirty-four minutes. Thirty-four minutes later, that "heartbeat" hidden in the base's shadows would pulse toward New York once more. And this time, they were ready.

But events rarely followed the schedule they had planned.

Three days later.

11:47 p.m., Third Action Squad office at the base.

Lin Xiao sat at his desk, the desk lamp casting a yellow circle of light across its surface. Within it lay a detailed map of the base, its paper rough and its edges worn. He marked the map with red and blue pencils—red for surveillance blind spots, blue for possible escape routes. The pencil rasped across the paper, unnaturally loud in the silent room.

The air was thick with the mixed smell of old paper, dust, and rusted metal. The heating pipes hummed dully within the walls, occasionally accompanied by the muffled thud of water striking the pipe walls. Outside, the temperature had already dropped below freezing, and a thin layer of frost coated the glass. Through it, the searchlights looked blurred and distorted.

Lin Xiao's fingers moved across the map.

The northwestern perimeter wall—there was a drainage outlet there, wide enough for an adult to crawl through. Its opening was sealed with wire mesh, but the degree of corrosion... He picked up a magnifying glass and carefully examined the detailed note marked on that area of the map. It was handwritten in Russian, the scrawl messy: "Replaced in 1987. Galvanized steel. Estimated lifespan: 25 years."

It was now 2011.

Twenty-four years.

He set down the magnifying glass and drew a small red circle around that spot. Then he picked up the ruler beside him and measured the distance from the outlet to the nearest patrol post—seventy-three meters. Four container yards lay between them, providing cover.

The pencil slid over the paper.

Then a sound came from outside the door.

Not footsteps. Not a knock. It was an extremely faint tapping sound, nearly impossible to notice. Three long taps, two short. A two-second pause, then repeated once.

Three long, two short. Repeated once.

Lin Xiao's fingers stopped.

The pencil tip hovered over the paper, half a centimeter from the small red circle. He raised his head and looked toward the office door. It was a heavy metal door painted army green, the paint peeling away to reveal dark red rust underneath. The brass handle reflected a dull glint beneath the desk lamp.

The tapping came again.

Three long. Two short. Pause. Repeat.

Lin Xiao put down the pencil. It rolled to the edge of the map and stopped beside the words "northwestern perimeter wall." He rose slowly without making a sound. The chair legs scraped lightly against the concrete floor with a faint creak. He walked to the door and placed his hand on the handle.

The metal handle was cold and rough beneath his palm.

He did not open the door immediately.

He pressed his ear against it and listened to the movement outside. The corridor was quiet, with only the low-frequency hum of the ventilation system in the distance. But beneath that hum, he caught two sets of breathing—one steady and deep, belonging to Su Ying; the other lighter, faster, carrying a tense rhythm.

A stranger.

Lin Xiao removed his hand from the handle and reached behind his waist. A Glock 17 was tucked there, its frame cold. He checked the safety, then gripped the handle again.

He turned it.

The door opened a crack ten centimeters wide.

The corridor was brighter than the room. White fluorescent tubes ran in two rows across the ceiling, their light harsh. Lin Xiao narrowed his eyes and saw Su Ying's face through the gap. Her expression was calm, but her eyes held something familiar to him—alertness, and a trace of barely perceptible urgency.

"Come in," Lin Xiao said, keeping his voice low.

Su Ying slipped inside sideways, moving as smoothly as a shadow. Someone else followed behind her—small and agile, wearing a dark gray hoodie with the hood pulled low over most of her face. She made almost no sound as she entered, as though the soles of her shoes were gliding across the floor.

Lin Xiao shut the door at once.

The lock clicked softly, and the sound of metal striking metal seemed especially clear in the silence.

Inside the room, the three of them stood beyond the desk lamp's circle of light, their shadows stretched long across the walls. Lin Xiao watched the stranger, his hand still resting behind his waist. Su Ying walked to the desk and reached over to switch off the lamp.

The room plunged into darkness.

Only the searchlight outside shone through the window, sweeping past once every fifteen seconds and casting swiftly moving patches of light over the walls and floor. Whenever the light passed, it briefly revealed the three silhouettes—Lin Xiao by the door, Su Ying leaning against the desk, and the stranger standing in the center of the room like a motionless statue.

"Clear," Su Ying said. Her voice sounded especially distinct in the dark. "I checked. No one's in the corridor. The surveillance cameras are undergoing their routine fifteen-minute maintenance. We have eight minutes left."

Lin Xiao did not move.

His eyes had adapted to the darkness, and he could make out the stranger's outline—about one meter sixty tall, slender, with narrow shoulders. The hoodie's hood was still pulled low, revealing only the shape of her chin and a lock of dark hair spilling out from beneath its brim.

"Who is she?" Lin Xiao asked.

Su Ying did not answer immediately. She went to the window, lifted a corner of the blinds, and looked outside. A searchlight beam swept past at that moment, illuminating the side of her face before quickly moving away. Her voice came from the darkness. "Nightingale. She used to be my informant. Top-tier hacker."

An informant.

A hacker.

Several possibilities flashed through Lin Xiao's mind. S.H.I.E.L.D.'s peripheral intelligence network was tangled and complex; some informants did not even know exactly who they worked for. But Su Ying had said "used to be"—which meant that relationship had ended, or changed.

"What is she now?" Lin Xiao asked, still watching the stranger.

"A fugitive," Su Ying said emotionlessly. "She's evading S.H.I.E.L.D.'s internal purge, as well as Hydra's pursuit. I ran into her while collecting supplies from an outer safehouse tonight. Two teams were tracking her. One was a S.H.I.E.L.D. tactical squad, standard setup, four people. The other..." She paused. "They were in plain clothes, but their operational style matched a Hydra infiltration team. Six people."

Lin Xiao's fingers lightly brushed the pistol grip.

"Why did you bring her here?" he asked.

"Because she needs somewhere to hide." Su Ying turned around to face Lin Xiao in the darkness. "And because she has information we need."

"Information we need?"

"About the report you sent."

The room went quiet for several seconds.

The searchlight swept past again. This time, Lin Xiao saw the stranger called Nightingale raise her head. Her hood still concealed her face, but Lin Xiao could feel those eyes watching him in the darkness.

"Turn on the light," a voice said.

It was a young woman's voice, slightly high-pitched, but with a calmness that did not match her age. She spoke English with a faint Central European accent—possibly Polish, possibly Czech.

Lin Xiao did not move.

"Turn it on," Su Ying said. "We don't have much time."

Lin Xiao walked to the desk and switched the lamp back on.

The yellow circle of light returned, illuminating the map spread across the desk and the red pencil that had rolled to its edge. The light spread outward and revealed all three faces.

At last, Lin Xiao saw what Nightingale looked like.

She pulled down her hood.

She had a young face, no older than twenty-five. Her skin was pale in the way of someone who had spent too long indoors. Her dark brown hair was cropped short around her ears, its uneven ends looking as though she had cut it carelessly herself with scissors. Her eyes were light gray, her pupils contracting into two tiny points under the light, and her gaze was sharp as a blade.

But her eyes were not the most striking part of her face—there was a fresh scrape across her left cheekbone, the blood crust not yet fully set; the corner of her mouth on the right was swollen and red, as if someone had punched her; several dark red strangulation marks ringed her neck, especially glaring against her pale skin.

She had just been through a fight.

Or rather, an escape.

Nightingale ignored Lin Xiao's assessing gaze. She walked straight to the desk and pulled something from her hoodie pocket—a modified tablet with a black casing, silver tape wrapped several times around its edges, and two fine cracks across the screen. She pressed the power button. The screen lit up, blue backlight reflecting off her face.

"I know who you are," she said, her eyes fixed on the screen while her fingers moved swiftly over the touchscreen. "Lin. Or rather, I know who you're supposed to be—a peripheral undercover agent in the S.H.I.E.L.D. files, one who was nearly forgotten. Designation SHD-7743. Your last active record was November 2009, during a low-risk intelligence-gathering operation in Kyiv. After that, you went dormant."

She spoke quickly, every word clear and precise.

Lin Xiao said nothing.

He walked to the desk and stood opposite Nightingale. A table lay between them, the unfolded map across it like a tangled battlefield. Su Ying stood by the window with her back to them, listening for movement outside.

"The files say you were reactivated three months ago," Nightingale continued, pulling up an interface on the tablet. It was the login page for S.H.I.E.L.D.'s internal archive system. The username field was already filled in: SHD-7743. The password field was empty.

"But what's interesting is," she said, lifting her head and looking straight into Lin Xiao's eyes with her pale gray gaze, "the signals I monitored show that someone recently sent something interesting through your dead drop."

Dead drop.

Lin Xiao's pupils tightened slightly.

S.H.I.E.L.D. had set up a dead drop for every peripheral undercover agent—a one-way communication channel used to transmit emergency intelligence. Each dead drop had a unique encryption protocol and physical location, known only to the agent and their designated handler. Lin Xiao's dead drop was in Vienna, in a drainage pipe beside an old phone booth. He had not used it in three years.

Until three days ago.

"How were you monitoring my dead drop?" Lin Xiao asked calmly.

"Because I've been monitoring the communications channels of every active and dormant peripheral undercover agent," Nightingale said as though it were the most natural thing in the world, like saying she drank coffee every morning. "For two years. At first, it was just an interest. Then it became a habit. Then..." She smiled, tugging at the wound on her mouth until a thread of blood seeped out. "It became a survival skill."

She lowered her head and operated the tablet rapidly.

The screen changed to a data stream log. Dense code and numbers scrolled down the display at a dizzying speed. Nightingale tapped the screen a few times, filtering the stream until only several lines of key information remained.

"Look here." She tapped the screen with her fingertip.

Lin Xiao bent closer.

Timestamp: 2011-12-07 22:13:44 UTC

Protocol Type: SHD-ENCRYPT v3.2

Packet Size: 1.7MB

Source Address: Vienna, Austria

Destination Address: S.H.I.E.L.D. Headquarters, Washington, D.C.

"This is the report you sent," Nightingale said. "Its encryption level is the standard emergency communications protocol for peripheral undercover agents. In theory, it should have gone directly to the central server at S.H.I.E.L.D. headquarters, where your handler would receive and decrypt it."

Her finger slid downward.

The data stream continued scrolling.

"But the problem is here." She tapped the screen again.

Timestamp: 2011-12-07 22:13:47 UTC

Event: Data Packet Intercepted

Interception Protocol: Unknown Encryption Layer (Quantum Key Signature Detected)

Redirect Address: Virtual Node Cluster (17 Hops)

Lin Xiao stared at the line.

The data packet had been intercepted.

It had been intercepted only three seconds after transmission. That meant that the instant his report left Vienna, something had seized it halfway through. It was not S.H.I.E.L.D.'s routine review process, nor was it Hydra surveillance—it was an interception method more advanced and more covert.

"Quantum key signature?" Lin Xiao asked.

"It's only a detected signal pattern. I'm not sure whether it's actual quantum encryption," Nightingale said, her fingers continuing to work. "But one thing is certain: the protocol that intercepted your report has an encryption level far beyond S.H.I.E.L.D.'s standard protocols. I tried seven cracking algorithms. Every one failed. This isn't conventional."

She pulled up another record.

A map appeared on the screen—a world map with a red dotted line beginning in Vienna, crossing the Atlantic Ocean, and finally pointing toward North America's eastern coast. Over the ocean, the dotted line split into more than a dozen branches, each representing a virtual hop.

"I tracked the packet's route after it was redirected," Nightingale said, sliding a finger across the map. "Seventeen hops, routed through servers in nine countries. The final three even used satellite links. By the time I traced it that far, the signal had become extremely weak. I could only lock down a general area."

Her fingertip stopped on a point on the map.

New York.

"Fuzzy geographic coordinates, with an error radius of around five kilometers," Nightingale said. "The packet finally disappeared in this area. I tried to narrow it down further, but the signal was completely blocked here—not conventional electromagnetic shielding, but something... more advanced."

She lifted her head and looked at Lin Xiao.

"Your anonymous report never reached S.H.I.E.L.D. headquarters directly. It was hijacked mid-transmission by an encryption protocol. The fuzzy geographic coordinates of the virtual node at the final hop... point to New York."

The room fell silent.

The desk lamp cast the shadows of the three of them over the desk. Outside, the searchlight swept past, its patch of light moving rapidly across the wall before vanishing. The heating pipes hummed low, and the sound of flowing water echoed inside the walls.

Lin Xiao stared at the point on the map.

New York.

Countless possibilities flashed through his mind. S.H.I.E.L.D. headquarters was in Washington, D.C., but New York had Stark Tower, early Avengers safehouses, and... hidden projects lurking in the shadows, projects that even Nick Fury might not fully control.

"The encryption style of the signal hijacker," Nightingale continued, lowering her voice, "looks a lot like... something from inside S.H.I.E.L.D., but not the kind used by its regular departments."

She opened another interface.

Two blocks of code appeared side by side on the screen. The left was labeled "SHD-STANDARD" (S.H.I.E.L.D. Standard Encryption), while the right was labeled "INTERCEPT-PROTOCOL." Their structures were similar—both were multilayered, both used dynamic keys, and both had timestamp verification.

But in the details, the differences were obvious.

"Look here." Nightingale pointed to one line in the code on the right. "The standard protocol uses 256-bit AES encryption, but the interception protocol uses an algorithm I've never seen before. And here—the standard protocol's key exchange is RSA-based, but the interception protocol..." She frowned. "I analyzed it for three days and still couldn't figure out its key exchange mechanism. It seems to... not need key exchange."

"What does that mean?" Su Ying asked as she walked over from the window.

"It means the encrypting and decrypting parties may share some preconfigured key that doesn't need to be transmitted through communication channels," Nightingale said. "Or worse—the encrypting side has technology capable of generating matching keys in real time. Either way, this is beyond what civilian or military technology can achieve at this stage."

She put down the tablet, braced both hands against the desk, and leaned forward.

Her pale gray eyes looked especially sharp beneath the lamp.

"Whoever hijacked your report is someone inside S.H.I.E.L.D., or at least someone who can access S.H.I.E.L.D.'s core encryption technology. But the protocol isn't from a regular department. It's some kind of... privately customized system. It resembles the encryption style of a private individual or a special project."

Private.

Special project.

A name flashed through Lin Xiao's mind.

Tony Stark.

But Stark should have been busy handling Stark Industries' transition, developing the Mark-series armor, and dealing with congressional hearings. Would he be interested in intercepting a report from a Hydra peripheral undercover agent?

Probably not.

Then who was it?

A private project of Nick Fury's? Some secret department within S.H.I.E.L.D.? Or... something else?

"Why are you telling me this?" Lin Xiao asked Nightingale.

Nightingale straightened and rubbed the strangulation marks on her neck. Her movements were gentle, but Lin Xiao noticed that her fingers were trembling—not from fear, but exhaustion. The long escape and constant tension had pushed her body to its limit.

"Two reasons," she said, a trace of fatigue finally entering her voice. "First, Su Ying saved my life. If it hadn't been for her tonight, Hydra's infiltration team would have dragged me into some basement by now. Second..."

She paused, her pale gray eyes looking directly at Lin Xiao.

"I saw what was in your report."

Lin Xiao's fingers tightened slightly.

"You cracked my encryption?" he asked, his voice still calm.

"Not completely," Nightingale said. "But your report used the standard emergency communications protocol for peripheral undercover agents, and that protocol... I cracked it two years ago. Not to steal intelligence. Just to test my skills."

She walked to the desk, picked up the red pencil, and spun it between her fingers.

"I saw the keywords," she said, stopping the pencil on her fingertip. "'Blood Axe Project,' 'biological modification,' 'experiment out of control,' 'high-level infiltration.' And... 'recommend immediate action.'"

She looked up.

"You were warning S.H.I.E.L.D. that some radical Hydra faction was advancing a dangerous experiment, and that the experiment had already gone out of control. You were advising them to act before the situation worsened."

The pencil spun once between her fingers.

"But your report was intercepted," she said. "That means either someone inside S.H.I.E.L.D. doesn't want it reaching headquarters, or... a third-party force is monitoring every intelligence stream connected to Hydra."

She set down the pencil. It rolled to the edge of the map and stopped beside the words "northwestern perimeter wall."

"Either way," Nightingale said, "you've been exposed. Not as an undercover agent—that identity may have been compromised long ago—but as... someone who knows too much."

The room fell silent again.

Outside, the searchlight swept past, its patch of light moving across the wall before disappearing. In the distance came the sound of a patrol vehicle's engine, growing closer, then fading away again until it vanished into the night.

Su Ying walked to the door and pressed her ear against it for a moment. Then she turned and nodded at Lin Xiao.

"The maintenance window is over," she said. "The cameras will be back online in two minutes."

Lin Xiao looked at Nightingale.

The young hacker stood beside the table, her body swaying slightly as she clearly forced herself not to collapse. The wound on her face was still seeping blood, and the strangulation marks on her neck looked dark purple beneath the light. Her eyes held something complicated—wariness, exhaustion, and a trace of... expectation.

What was she expecting?

Shelter? Cooperation? Or something else?

"How long do you plan to stay here?" Lin Xiao asked.

"Until the pursuers leave this area," Nightingale said. "Hydra's infiltration teams never remain in the same place for more than forty-eight hours. That's their operational doctrine. As for S.H.I.E.L.D.'s team... it depends on the mission priority. My priority isn't high. They'll probably search for three days, then withdraw."

"Three days," Lin Xiao repeated.

"Yes," Nightingale said. "After three days, I'll leave. I won't cause you any trouble."

She paused, then added, "In exchange, I can help you with one thing. Anything involving networks, data, or communications. Cracking, tracking, forging, blocking... your choice."

Lin Xiao did not answer immediately.

He went to the window and lifted one corner of the blinds. Outside, the base lay shrouded in night. Searchlight beams swept across the darkness in crossing arcs, like blades cutting through the black. On the distant perimeter wall, the sentries' shadows stretched long beneath the lights.

Three days.

For three days, this hacker named Nightingale would stay in this room. What would she see? What would she hear? How much would she learn about this base, about Lin Xiao, about Su Ying?

Risk.

But also an opportunity.

A top-tier hacker who could crack S.H.I.E.L.D. encryption protocols, track hijacked data packets, and escape the encirclement of two pursuing teams—someone like that was not easy to come across.

"You sleep there." Lin Xiao pointed at a folding cot in the corner of the room. Wolf occasionally used it when he stayed up late. Its gray sheets had been washed until they had faded white.

Nightingale glanced at the cot and nodded.

"Thank you," she said softly.

Lin Xiao went to the table and began clearing away the maps. He returned the red and blue pencils to their holder, carefully folded the maps, and tucked them into a drawer. Then he switched off the desk lamp, plunging the room into darkness once more.

Only the searchlight filtering in through the window swept over the room once every fifteen seconds.

Between the passing pools of light, Lin Xiao saw Nightingale walk to the folding cot, sit down, then lie back. Her movements were light, almost soundless. Su Ying went to a chair on the other side of the room and sat down, closing her eyes as she adjusted her breathing—the way agents remained alert while resting.

Lin Xiao sat in his own chair.

In the darkness, his eyes were fixed on the ceiling.

New York.

The hijacked report.

The custom-designed encryption protocol.

These fragments spun and connected in his mind, but one crucial piece was still missing—the motive. Why intercept that report? To protect Hydra's radical faction? Or for... something else?

He remembered the anomalous data packet Wolf had discovered.

Every two hours and seventeen minutes, it was sent from inside the base, bound for New York.

The same interval.

The same destination.

Coincidence?

Or...

The searchlight outside swept past again, its beam racing across the wall before vanishing. In the darkness, Lin Xiao heard Nightingale breathing—steady and deep. She had fallen asleep.

After fleeing for who knew how many hours, the young hacker had finally found a place where she could rest for a while.

And Lin Xiao knew that this peace would not last long.