The blue light inside the insulated box flashed again.

Chen Hao stared at the light, his finger still hovering in mid-air. That flash didn't seem like a reflection; it looked more like a pulse emanating from within the crystal. He didn't speak, but simply pushed the box towards Nana.

“It moved again,” he said.

Nana raised her left arm, aiming the scanner at the insulated box. Her right arm armor was still emitting steam, and her movements were a beat slower than before. She didn't complain, but the system interface flickered, like stuck gears finally meshing.

“The signal frequency is the same as last time,” she said. “The interval is thirty-seven seconds, and the error is no more than 0.2.”

"Not random?" Susan crouched down, her hand on the pliers, her eyes never leaving the box.

“No,” Carl leaned closer. “It’s more like… a response to something.”

No one answered. The cave was so quiet that the hum of the terminal cooling fan could be heard. Chen Hao looked down at his worn-out shoes; the soles were cracked in two, and walking on them felt like dragging two pieces of scrap metal.

“Then sweep it,” he said. “Take it apart and see.”

“We can’t open it directly,” Nana said. “The pulses emitted by the crystal will interfere with high-precision equipment. The last scan was interrupted because we were too close.”

"Then wrap it up." Chen Hao grabbed a metal piece from the lining of the insulated box. "Didn't you say this thing can insulate against heat? Let's see if it can block the signal."

Carl took the materials, tore off a piece of insulating tape, and began wrapping it around the outside of the insulated box. Susan cleared the terminal cache and closed all unused programs. Nana accessed the database and searched for mineral resonance spectra.

The screen flashed, and a series of waveforms appeared.

“Multiphase silicon-based composite crystal clusters,” she read aloud. “They selectively absorb blue-violet wavelengths of energy and are commonly found in high-pressure, low-temperature crystallization environments.”

“It’s not cold here.” Chen Hao touched the rock wall, and his palm immediately became hot.

“But it adapted,” Nana said. “The structure changed. Now the crystal can not only absorb energy, but also store it and release it slowly.”

"Frequency stabilizer?" Karl looked up.

"similar."

"Then what did it sense when it flashed just now?"

Nana didn't answer. She switched the detector to passive receiver mode and aimed it back at the insulated box. A few seconds later, a faint curve appeared on the screen.

“There are external signals,” she said. “They are weak, but they follow a pattern.”

Where did it come from?

“Deep in the new area.” She pointed to the passage ahead, “the fluctuation frequency and the crystal response window match by 86 percent.”

Chen Hao grinned: "You mean, this thing is talking to the thing inside?"

"More accurately, it is receiving echoes."

"echo?"

“The fluctuations released by the energy core are refracted through the rock strata, and their arrival here is delayed.” Nana pulled up the previous detection data. “The fluctuations we recorded are not real-time data, but feedback from seven minutes ago.”

“So it’s not jumping around randomly.” Susan understood. “It’s adjusting its output based on that echo.”

“Yes.” Nana nodded. “This means that the fluctuations are cyclical, not continuously increasing.”

The cave fell silent.

Carl put down his tools and stared at the terminal screen. Susan slowly released the pliers. Chen Hao sat down on the ground, leaning against a piece of cooled molten slag.

"So..." he lowered his voice, "we've been afraid of going in the wrong direction all along?"

“Previous data were all surface readings,” Nana said. “Now that we have crystals as a reference, we can build new models.”

"Let's do it." Chen Hao stood up. "Then let's build it."

For the next half hour, no one spoke. Carl made a shield out of a discarded battery casing and sealed the insulated box inside. Susan was responsible for monitoring the terminal's operating status and clearing the memory as needed. Nana collected the crystal response data in segments and manually recorded the peak value every thirty seconds.

The system suddenly alarmed during the third sampling.

“Pulse enhancement,” Nana said. “Amplitude increased by forty percent.”

"Is the shielding layer failing?" Karl reached out to check the seam.

“No,” Nana said, staring at the screen. “The external signal has changed. The fluctuation frequency is increasing.”

How often?

“A cycle is 42 seconds.” She quickly pulled up the chart. “The rising phase lasts for 20 seconds, then it falls back, with a brief quiet period in between.”

“Like breathing,” Susan said.

“It’s more like the tides.” Nana began to draw the curves. “The rise and fall are regular, and the amplitude is stable.”

"Draw it." Chen Hao handed over a waterproof paper.

Susan took the pen and traced the lines on the screen. A distinctly undulating waveform gradually took shape, with a peak at intervals followed by a gentle decline.

"This is... an energy tide diagram?" Chen Hao looked at the diagram.

“Let’s call it that for now,” she said. “If this rhythm continues, we can calculate the next peak time.”

"when?"

"Fifty-three minutes later."

The cave fell silent again.

Chen Hao stared at the diagram, his fingers unconsciously tapping his knee. Carl fiddled with the shielding, confirming there were no gaps. Susan folded the drawing and stuffed it into a waterproof bag. Nana continued monitoring the data; the system interface had become much more stable.

“What if we can get the crystal in place before the peak?” Chen Hao suddenly said.

"What's the meaning?"

“Since it can absorb specific frequencies and resonate with the echoes inside…” he pointed to the diagram, “could we use it as an ‘anchor point’ to deflect the energy a little?”

“It’s not about shutting down the core,” Nana continued, “but rather guiding the flow.”

“Right.” Chen Hao smiled. “Use their strength against them.”

“The risk is very high.” Carl frowned. “The operation must be precise. Even a difference of a few seconds could trigger a recoil.”

“The protective suits won’t last long,” Susan added. “Working in high temperatures is too physically demanding.”

“So we can’t just send one person,” Chen Hao said. “We’ll deploy in stages. First, we’ll place a set of crystals at the mid-level nodes to form a buffer zone, and then gradually advance.”

“A triggering device is needed.” Karl thought for a moment. “The timing of spontaneous discharge of the crystal is unstable and needs to be controlled manually.”

"Can you do it?"

“Modify the circuitry of the thermal box.” He pulled out his toolbox. “Add a delay switch and connect it to the pulse sensor. It will automatically activate when the external fluctuation approaches its peak value.”

How long will it take to get it done?

"One hour."

“We’ll make it.” Nana glanced at the time. “There are 51 minutes left before the next peak.”

“Then it’s settled.” Chen Hao stood up and stretched his limbs. “Nana, Susan, and I will go ahead to scout the way, while Karl will stay behind to work on the device. Once we find a suitable location, we’ll send a signal, and you can bring it up when it’s ready.”

"Are you sure you want to put the crystal in?" Susan asked.

"Otherwise what?" Chen Hao looked at the insulated box. "We carried it around for ages, wasn't it just for this?"

"But what if it gets out of control..."

“Then run faster,” he said. “Anyway, my shoes are worn out, so running barefoot is easier.”

No one laughed.

But the atmosphere relaxed a bit.

Carl began disassembling the circuit board, his fingers deftly stripping the wires. Susan checked the pliers and the sealed bag, confirming they were both usable. Nana restarted the scanning program, locking onto the energy gradient changes in the forward channel.

Chen Hao picked up a small crystal fragment and twirled it in his hand.

"Why do you think it chose us?" he suddenly asked.

"What?"

"This thing," he waved his hand, "knows we're coming? Or can anyone just grab it?"

Nana glanced at him.

“It’s impossible to tell at the moment,” she said, “but it is indeed waiting for some kind of trigger.”

"for example?"

"For example... the correct frequency."

Chen Hao put the fragments into his pocket and patted it.

"Then don't make it wait too long."

Carl finished soldering the last wire and put the modified device into his toolbox. Susan put away the blueprints and stood up. Nana shut down the non-essential systems, leaving only the basic detection functions enabled.

The four people gathered around the insulated box.

The blue light flashed again, as punctually as a clock.

Chen Hao reached out, opened the shield, and took out the crystal.

“Let’s go,” he said. “It’s time to get to work.”

They moved along the passage, their footsteps crunching on the molten slag. The air grew hotter, and their breathing became heavy. Nana led the way, her detector constantly updating its data. Susan followed closely behind, her hand always resting on the pliers. Carl carried his toolbox, walking cautiously. Chen Hao brought up the rear, his eyes constantly on the timer on his wrist.

Forty-seven minutes remaining.

After rounding a bend, a sunken platform appeared ahead, with obvious cracks in the rock wall and a temperature several degrees lower than the surrounding area.

“This is a good spot.” Nana stopped. “The geological structure is stable, making it suitable for setting up the first node.”

Chen Hao nodded: "Right here."

Carl put down his backpack and took out the device. Susan helped fix the crystal's position. Nana started the countdown synchronization program. Chen Hao stood by, watching them work.

“The device is ready.” Carl pressed the test button, and the indicator light turned green.

"Time synchronization." Nana connected the signal.

“Ready.” Susan took a step back.

Chen Hao took a deep breath and looked at the main crystal in the insulated box.

“Let’s get started,” he said. “Let’s see just how smart this thing really is.”