The submersible was still sinking, and the numbers on the instrument panel were jumping up and down.

Chen Hao stared at the darkness outside the starboard side. The feeling of pressure on his chest had disappeared, but his hand was still hanging in mid-air, as if he had forgotten to retract it.

“Particle adsorption has not occurred again,” Nana’s voice came from the back seat. “But the coating recorded three weak resonances, with inconsistent frequencies.”

"What do you mean?" Chen Hao turned his head. "It got touched again?"

“It’s not touching,” Nana said. “It’s scanning.”

Susan looked up: "Who's sweeping us?"

“I don’t know.” Nana pulled up the data stream. “The signal source is not within the sonar coverage area, its direction of movement is opposite to ours, and its speed is constant.”

Carl gripped the joystick: "It's probably the ocean current that caused the object to reflect."

“But the trajectory is straight,” Nana said. “It lasts for seventeen seconds, with an offset angle of less than 0.1 degrees.”

The cabin was quiet for a few seconds.

Chen Hao suddenly laughed: "So there are things lined up on the seabed waiting for us to come and inspect them?"

No one responded.

He didn't expect anyone to answer.

Telling jokes at times like these is to prevent the silence from becoming too heavy.

"Let's stabilize the navigation first." Susan looked down at the screen. "The magnetic field disturbance is stronger than expected, and the yaw is four degrees."

Carl switched to inertial positioning: "Using terrain markers for correction, the edge of the canyon is just ahead, and there's a rock ridge that can be used as a reference."

“Then let’s stick close to it.” Chen Hao stood up. “I’ll go check if there are any traces left on the outer deck.”

“You can’t get out,” Susan said.

“I know.” He walked to the locker and opened the drawer. “But I can check the blind spots of the surveillance. If that particle could really penetrate the coating, it might have left a mark on the outside.”

Nana nodded: "That makes sense."

Three minutes later, Chen Hao leaned over the observation window, magnifying glass in his hand. The coating of the new diving suit gleamed darkly under the low pressure, like a wet stone that had just been wiped clean.

“The middle right side,” he pointed to the screen, “there’s a small patch here that’s a different color, like a layer has been rubbed off.”

Nana accessed camera data: "Upon zooming in, fine scratches are visible, arranged in parallel with uniform spacing."

"Man-made?"

"Highly likely."

Susan frowned: "Who can row our boat thousands of meters underwater, using what?"

“Never mind who it is,” Carl said. “We need to figure out what it wants to do.”

“Maybe it’s just passing by.” Chen Hao sat back down. “Like a deep-sea nail spirit that deliberately pokes at passing tin cans.”

“Let’s assume it’s an active behavior,” Nana continued her analysis. “The purpose might be to collect samples or transmit signals.”

"What are you sending?"

"unknown."

"Did it receive it?"

"uncertain."

Chen Hao grinned: "I hope our outer shell doesn't taste good."

No one laughed.

But he didn't care.

He knew that saying something absurd at this point would at least keep everyone from staring at the skewed flight path on the screen.

"An unusual reflection has been detected on the left," Nana suddenly said. "It's 1,200 meters away, located on the side of a cliff, and has obvious metallic features."

Carl adjusted the course: "The current is a bit turbulent; we can't get too close."

“Send a drone,” Susan said.

“No,” Nana replied. “The magnetic field interference is too strong, and small devices are prone to losing connection.”

Chen Hao stroked his chin: "Then we'll have to clear the area manually."

How will you clean it?

“Use our new coating.” He stood up. “Can’t it spray temperature-controlled fluid? Remotely flush the rock surface, wash away half the mud and sand, and see if there’s stone or a key underneath.”

“The risks are considerable,” Susan said. “The slope there is close to seventy degrees, and the operating space for the robotic arm is limited.”

"It's better than guessing blindly."

Five minutes later, the temperature-controlled nozzle activated. The hot water flowed under high pressure, turning into a mist that swept across the rock face. The mud and sand were washed away, revealing a smooth, grayish-white surface underneath.

“It doesn’t look like natural rock,” Carl said.

“It’s not ordinary ore either.” Susan zoomed in on the image. “The reflectivity is too high, and the edges are too regular.”

Nana maneuvered the robotic arm closer: "Prepare to sample."

As the mechanical claw extended, a turbulent current crashed into it, causing the submersible to sway.

"Hold on!" Karl gripped the handrail tightly.

The claw veered off course by half an inch, grazing the edge of the target.

"One more time."

The second time, the claw tip got into the gap and gently pried it open.

A small, silvery-gray flake detached and was sucked into the sampling chamber.

"Got it." Chen Hao leaned closer to the screen. "This thing is quite square."

"It measures 15 by 8 centimeters." Nana took the item. "It's 1.2 millimeters thick and weighs less than 300 grams."

"How can something this light get embedded in a stone?"

“It wasn’t embedded.” Susan put on gloves to examine it. “It was covered by sediment later. The cut is clean, clearly done manually.”

"What about the material composition?"

"It contains titanium, tungsten, silicon, and trace amounts of cerium and neodymium," Nana input into the detector. "Its corrosion resistance exceeds current industrial standards by three levels."

Who did it?

"Unable to match an existing database."

"That's an antique."

"It could also be a new technology."

"But we don't have that ability."

"So it's more likely the former."

The cabin quieted down.

Everyone understood what this meant.

They found something that didn't belong to this era.

“There are scratches on the surface.” Susan held the film up to the light source. “At first I thought they were scratches, but now they look like symbols.”

Chen Hao leaned closer: "It's all winding and twisting, like someone got a cramp halfway through doing their homework."

“The arrangement is regular.” Nana pulled up the scan image. “It’s a circular distribution with a raised center and six sets of lines radiating outwards from it.”

"Like the sun?"

"It doesn't look like it."

"Like a watch face?"

"No numbers."

"Like a Wi-Fi signal?"

"No launch source."

"Then tell me what it looks like?"

Nana didn't say anything, but instead imported the image into the knowledge database.

Filtering begins.

First time, no match.

The second is to exclude modern civilization marker systems.

The third time, the late pre-Geological Period classification model was used.

When the progress bar reaches 89%, a notification sound will play.

[Highly similar structures discovered]

[Matching Target: Map of Remnants of Civilization at the Bottom of the Pacific Ocean - Branch 3]

Similarity: 86%

“This is a map,” Nana said.

What map?

“Topographic guidance map.” She pulled up the simulation stitching results. “These kinds of symbols are often used to mark resource points or safe routes. The original map should be circular; this fragment belongs to the lower right area.”

"Where does it point?"

“Combining the previous hotspot exploration,” Nana overlaid the images, “the marker points completely overlap with the cave system discovered in Chapter 654.”

Chen Hao slammed his hand on the table: "We've been working for nothing! Turns out they'd already drawn up the route?"

“It wasn’t a wasted effort,” Susan said. “If we hadn’t caught that creature, we wouldn’t have discovered the coating material, we wouldn’t have been able to upgrade our diving suits, and we wouldn’t have been able to get here.”

"So we're going according to the script?"

"It's more like filling in the gaps in the clues."

Carl looked out the window: "So, that place... really is man-made?"

"At least someone has been there."

"And it left a mark."

“There’s more than one.” Nana zoomed in on the image. “There’s still half a symbol missing from the edge, which means there may be other fragments nearby.”

“Then let’s keep looking.” Chen Hao stood up. “We’re already at the door, we can’t just knock and go home for dinner.”

“We haven’t confirmed its safety yet,” Susan cautioned.

"Nobody said it was definitely dangerous."

"But the particle scan just now—"

"Perhaps it's a welcoming ceremony."

"Are you planning to hold an exhibition underwater?"

"Why not?" He spread his hands. "People in ancient times left maps, and people in modern times leave QR codes, all to prevent later generations from getting lost."

Nana suddenly looked up: "There's a reaction on the back of the fragment."

"What was the reaction?"

"Fluorescent spots appeared after heating." She flipped the film over and exposed it to shortwave irradiation. "It flashes once every 3.7 seconds, with a stable interval."

"3.7 again?" Chen Hao's eyes widened. "The sonar anomaly just now also showed this number!"

“It’s not a coincidence.” Nana recorded the frequency. “It could be a signal protocol.”

"To whom should it be sent?"

"People who can accept it."

"Can we send it back now?"

"Technically feasible."

"Then let's give it a try."

"The risks are unknown."

"I didn't ask you to send telegrams saying 'I'm here,'" Chen Hao grinned. "Can't you at least burp?"

Susan sighed: "Can't you be serious for once?"

“I’m being very serious.” He pointed to the screen. “Look, it flashes once, and we flash once too, which is like saying hello. If it flashes again, it means it understands human speech.”

"This is not a code."

"It's communication."

"What if the defense mechanism is triggered?"

"That's still better than blindly charging forward."

Nana has begun setting up the signal feedback program.

Thirty seconds later, the coating on the starboard side of the submersible heated up locally, illuminating a brief pulse of light in the darkness.

A flash.

A pause of 3.7 seconds.

Another flash.

Then everyone stared at the external sensors.

One second.

Two seconds.

Three seconds.

...

Seven seconds.

There was no response.

"No chance," Chen Hao said, scoffing. "They think we're too unsophisticated."

Just then, a new notification popped up on Nana's terminal.

[Increased fluctuations in external magnetic field]

[Direction: straight ahead]

The intensity change conforms to the encoded sequence.

She decoded it quickly.

A few seconds later, a set of numbers popped up on the screen.

3.7, repeat eight times.

Then it was interrupted.

It was exactly the same signal that the sonar had captured before.

But this time, the message came directly from the front lines.

Chen Hao slowly sat up straight.

"It returned."

Nana nodded: "Response successful."

"So it knew we were here?"

“Not only did she know,” she said, looking at the data stream, “but she’s been waiting.”

Chen Hao smiled and reached out to touch the control panel.

"Then let's not make it wait too long."

He turned to Carl: “Turn around and head towards the marker.”

"Not reporting to base?"

"Let's talk about it after we find the door."

"Regulations from higher authorities—"

"The rules don't say you can't pick up maps."

Susan was about to say something when Nana interrupted her.

“A new source of metallic reflection has appeared in the rock strata 500 meters ahead.”

How big?

"Bigger than before."

"shape?"

"Approximately a perfect circle."

Chen Hao stood up and walked to the observation window.

In the depths of the black water, nothing can be seen.

But he knew something was waiting there.

The submersible slowly turned.

The thrusters restarted.

The water flowed, leaving a thin line as it slid towards an unknown direction.

Chen Hao's hand rested on the windowsill, his knuckles slightly white.