Sensing a New Threat, Raising the Guard

Ye Mo's right hand was still pressed against the scorched earth, his fingertips able to feel the increasingly rapid vibrations. Every seven and a half seconds, it felt like his heart was pounding in the emergency room. He didn't move, nor dared to breathe heavily, afraid that if he raised his hand, the signal would be cut off. But if he sat down any longer, he would break too— his Steel Bone right leg's reserve power was only 30% remaining, and the sparks at the joint had gone from occasional pops to continuous smoke, like a burnt-out electrical wire.

He gritted his teeth and pushed himself up, his knees making a dull thud, like a rusty hinge being forcibly pried open. His left leg landed first to steady himself, before daring to move his right leg. With each step, the pulse from the ground became clearer; he knew this thing was nearing its breaking point.

"It's not a false alarm," he said in a low voice, seemingly directed at no one, "It's really going to bomb."

He pulled out the encrypted transmitter hidden in the inside pocket of his work pants, swiped his finger across it twice, and selected the preset frequency. The screen lit up with a blue light, making half of his face appear bluish. He typed quickly, but every word was carefully chosen: [Not a false alarm, countdown started, target northwest, evacuate all unrelated personnel immediately]. After sending the message, he immediately shut it down and casually stuffed the transmitter into the pile of rubble—keeping it would serve as a tracking source; Ultron's specialty now was using signals to turn the tables.

He looked up at the half-collapsed command tower in the distance, its outer walls cracked like a dry riverbed, but a red light still flickered on its top— the Avengers' temporary base's identification beacon. He had to get back before that light went out.

He couldn't walk in a straight line. The ruins were full of debris and sinkholes, so he had to go around them. Steel Bone right leg started to alarm after three minutes, and the system popped up a small message: "[Insufficient energy, hibernation recommended]". He slapped his thigh with his palm, shaking the message box away.

"Shut up, I don't have time to fix you right now."

He finally reached the base entrance. An alloy gate lay across the ground, originally upright but now warped and stuck in its tracks. He squeezed through sideways, scraping off a layer of skin from his shoulder, blood mixed with ash dripping down. The interior was dimly lit; emergency power only supplied the main passage, leaving the rooms on either side completely dark.

The control room was at the end of the corridor. The door was open, and Tony was fiddling with the control panel with his back to the door. He was only half-wearing his armor, and the reactor on his chest was glowing blue, matching the color of the screen in front of him. Captain America stood in front of the sand table, a pen in his hand, staring at the map without moving. Thor sat on a bench in the corner, Mjolnir beside his lap, his head slightly lowered, as if resting. Black Widow and Hawkeye stood against the wall, one looking at the monitor screen, the other checking the bow and arrows.

No one spoke.

Ye Mo leaned against the door frame and took a breath. His voice wasn't loud, but everyone heard it.

Tony didn't even turn his head. "You're still alive? I thought you were planning to stay there until dawn."

"I'd like to too." Ye Mo walked inside, each step a little hesitant. "But I've discovered something, and if I don't tell you, I'm afraid I won't live to see dawn."

Captain America put down his pen, turned around, and said, "Get to the point."

Ye Mo didn't rush to speak. He first took off his glasses, wiped the dust off the lenses with his sleeve, and then put them back on. Then he walked to the main control panel and placed his hand on the interface slot. The residual signal from the Steel Bone neural network was automatically uploaded, the projector hummed, and a waveform appeared in the air—first jumping every thirteen seconds, then gradually shortening, and finally freezing at seven and a half seconds.

"What is this?" Tony leaned closer to take a look.

"Underground pulse frequency." Ye Mo leaned against the edge of the table, his left hand on the edge. "It's been decreasing from thirteen seconds to seven and a half seconds now, and it's still accelerating. The source is 180 meters to the northwest, 17 meters underground, at the original ventilation shaft location."

"It sounds like a time bomb," Hawkeye said.

"It's a bomb," Ye Mo nodded. "And a gravity trap of the O-09 level. I intercepted a fragment command; the keywords are ' Force Field calibration' and 'delayed detonation.' Ultron isn't out of the picture; it's rebuilding nodes underground, preparing to launch a double attack on us."

Tony stared at the waveform for a few seconds, then suddenly turned around and slammed his hand on the keyboard. "Connect to deep scan, retrieve geological data from the western region." The screen refreshed, displaying a three-dimensional structural map, with one point flashing red.

"Signal source confirmed," he said. "It's not a natural vibration, it's regular, and... it definitely looks like it's charging up."

Thor stood up, picked up his hammer, and said, "Let's not wait for it to explode; let's go down and demolish it now."

"No," Ye Mo shook his head. "We don't know how many defense mechanisms are below. Ultron remained silent throughout, without uttering a single wasted word, which means it has changed its strategy—no longer relying on numbers to overwhelm us, but on ambushes and sneak attacks. Rushing in rashly might play right into its hands."

"You mean it deliberately let us discover this signal?" Black Widow asked.

"It wasn't necessarily intentional." Ye Mo rubbed his temples. "But it knew we'd find out sooner or later. So it left this thread, letting us follow it, and then—" He made an explosion gesture, "Wiped us all out."

Captain America walked to the sand table, tracing the northwest area with his finger. "If we're correct, Ultron's goal is to create a localized collapse, cutting off the base's connection to the outside world, or even burying the command center directly?"

"Highly likely." Ye Mo nodded. "It failed last time because it couldn't beat us in a head-on confrontation. This time it's learned its lesson; it's not fighting anymore, it's resorting to underhanded tactics."

Tony sneered, "Does it really think we won't understand just because it changes its approach?"

"It's not that we don't understand it," Ye Mo looked at him, "It's that we can't defend against it. We don't even know exactly how it detonates. Is it through electromagnetic resonance? Or by using nanomechanical reconstruction of the geological structure? What if it doesn't intend to explode at all, but is just using this as a decoy, and its real killing move is somewhere else?"

After these words were spoken, the room became even quieter.

Thor frowned. "You mean, this is just a smokescreen?"

"I can't say for sure," Ye Mo said, shrugging. "I only know that the signal is real, and the countdown is real, but what's hidden behind it, I don't know. Ultron isn't as talkative as it used to be; it's learned to hide."

Tony paused for a few seconds, then suddenly ordered, "Cut off all non-essential power. Activate the deep defense protocol. Seal all external passages. Lower the internal partition doors. I want this place to be an impenetrable fortress."

"What about air units?" Hawkeye asked.

"MK-40 stand by, drone swarm take off for patrol, maintain silent mode," Tony said, quickly operating the controls. "Also, notify the outer perimeter sentries to evacuate to the safe zone, to be executed in five minutes."

Black Widow immediately connected to the tactical channel. "This is Black Widow. All outposts, take note. Retreat immediately. Repeat, retreat immediately. Codename ' Night Raven ' activated."

Captain America looked at Ye Mo: "You provide the intelligence, now it's your turn to add your assessment. What might Ultron do next?"

Ye Mo took a deep breath and began to speak, "First, its choice to remain silent indicates that it is no longer pursuing psychological suppression but has switched to covert attacks; second, its ability to rebuild underground nodes in a short time proves that it has local manufacturing and deployment capabilities, and may have hidden backup factories or miniature assembly pods; third, the countdown mode is similar to a physical fuse, which is most likely aimed at destruction rather than information warfare or psychological interference."

"So it was a real attack?" Thor asked.

"Yes." Ye Mo nodded, "It's not going to play games anymore. It's going to explode, it's going to collapse, it's going to make us lose our footing."

"Then let's not let it succeed." Captain America decisively ordered, "All personnel, enter Level Two combat readiness. Tony will be in charge of aerial reconnaissance and armored vehicle deployment; Thor will guard the high-altitude defense line to prevent the enemy from breaking through from above; Black Widow and Hawkeye will control the east and west wing monitoring networks respectively, and any abnormal movement must be reported immediately; Ye Mo will remain at the central command to continue monitoring signal changes and provide early warning of the final detonation moment."

"Understood," everyone replied in unison.

Tony glanced at the screen one last time, confirming the protocol was activated, then walked to the east technical area to begin debugging the armor's remote response system. Thor stood by the high window on the west side, his hammer hovering beside him, his gaze sweeping across the night sky. Black Widow sat down at the south intelligence terminal, her fingers rapidly typing on the keyboard, bringing up the footage from the external cameras. Hawkeye slung his quiver over his shoulder, checked the type of ammunition, then moved to the north armory entrance, ready to ascend to the high ground at any moment.

Ye Mo didn't move.

He dragged over a metal chair, sat down against the control panel, rested his left hand on his knee, and gently placed his right hand on the ground. The system was still cooling down, and his sensory abilities hadn't recovered, but he could still rely on the residual conductivity of his Steel Bone nerves to catch the vibration rhythm.

Time passed little by little.

No one spoke.

The lights were turned down to the lowest setting, plunging the entire base into a stifling silence. The only sounds were the ticking of instruments, the whistling of wind through cracks, the distant patter of water leaking from a pipe, and the pulses from underground gradually merging with the noise.

Seven and a half seconds... seven seconds... six and a half seconds...

He counted in his head.

After Tony finished adjusting his armor, he turned around and looked at him. "Are you alright?"

"It won't die." Ye Mo didn't open his eyes. "As long as it hasn't exploded, I can keep an eye on it."

"You don't look like you can hold out for long," Hawkeye interjected.

"This isn't the first time I've done this," Ye Mo said with a slight smirk. "Last time in Afghanistan, I went hungry for four days and still carried a generator on my way. This little injury is nothing."

Tony shook his head. "You're just bragging."

A few more minutes passed.

Black Widow suddenly said softly, "Outer perimeter search complete, no unusual movement found."

"Approaching without a target in the air," Hawkeye added.

"The protection protocol is fully activated," Tony confirmed.

Captain America stood before the sand table, hands gripping the edge, his gaze steady. "Everyone, stay alert. This isn't the end, it's the beginning. Ultron won't rely on this alone; we must be prepared for what comes next."

Ye Mo listened, his fingers still pressed against the ground.

The pulse lasted 6.5 seconds.

Six more seconds.

His eyelid twitched.

His right index finger trembled slightly, as if he had sensed something.

He knew it was coming soon.

Very fast.