Chen Hao moved forward, hugging the rock face, his foot breaking a small piece of stone. He immediately stopped and turned to look at the giant lizard. Fortunately, it was focused on the black rock on the ground and hadn't noticed them.

"Hurry up," Nana whispered. "It pauses for three seconds each time it touches the ground; this is the window."

The four men pressed on, with Carl in front, Susan in the middle, and Chen Hao bringing up the rear. They clung tightly to the rock like tiles, inching their way to the other side of the depression. The black rock was now right in front of them, its surface rough, with an extremely fine crack along its edge, almost invisible.

Nana leaned closer to scan, a glint of light flashing in her eyes. "Air movement, echoes inside, unknown depth. It's the entrance."

"I knew something was off about this rock," Chen Hao said, catching his breath. "The guards come to check in every day; there must be something hidden underneath."

“The problem now is, how do we get in?” Karl lowered his voice. “If we crawl in, the noise will definitely get out.”

“We need to lure it away.” Chen Hao stroked his chin. “Karl, you go around to the west and throw stones, not too far, just enough for it to hear you.”

"What if it doesn't leave?"

"That means it's holding back and really doesn't want to move," Chen Hao grinned. "Then let's not move either, and just wait for it to die of old age."

Nana glanced at him: "The probability is zero."

"I know," Chen Hao waved his hand, "but I'm just saying it for fun."

A few minutes later, Karl quietly circled around. Just as the monitor lizard lowered its head to touch the rock again, a crisp "snap" came from afar, like a pebble hitting a rock. The creature's ears twitched, it raised its head, stared in the direction of the sound for a few seconds, and then strode over.

"Now!" Chen Hao waved his hand.

The four quickly approached the crevice. Nana went in first to scout ahead, followed by Susan and Carl, and finally Chen Hao squeezed in, his hips tucked in. He had just slipped inside when he heard footsteps approaching from outside.

"It's back!" Susan held her breath.

Everyone lay still on the ground. A few seconds later, the shaking stopped, and the guard resumed its patrol. It found nothing amiss.

The entrance was narrow, allowing only one person to pass at a time. The passage inside sloped downwards, growing darker and darker as one went on. The air was damp, carrying a faint smell of rust. Chen Hao frowned, about to speak, when Nana stopped him with a gesture.

“There are biosignals ahead,” she said softly. “High-frequency activity, densely distributed.”

"What is that?" Chen Hao asked in a low voice.

"Bats are social species that rely on sound waves for navigation and have no vision."

Before the words were even finished, the rock wall above them trembled. Then, a vast expanse of greyish-white wings burst forth, too numerous to see clearly. They swooped down in droves, heading straight for the group.

"Crouch down! Cover your mouth!" Nana immediately activated her shield, creating a light blue barrier behind her to protect the three of them. At the same time, she emitted a high-frequency noise to interfere with the bats' navigation system.

The creatures thrashed about in the air, some crashing into walls and landing, others circling aimlessly. Yet a few still managed to break through the chaos and pounce on the group.

Susan accidentally stepped on a pebble with a snap. Instantly, a swarm of bats nearby turned and flew straight at her face.

"Ah!" She instinctively raised her hand to cover her face.

Carl reacted quickly, slapping off his coat and throwing it against the side wall. The sound of the fabric hitting the rocks attracted some bats, who turned and flew away.

"Run!" Chen Hao grabbed Susan and rushed forward.

The four hurried along, their backs bent low, with bats buzzing behind them. Only when the passage suddenly widened and the overhead space increased did the creatures cease their pursuit, turning back and disappearing into the darkness.

"Huff..." Chen Hao gasped for breath, supporting his knees. "This place doesn't even let people sleep in peace."

“That move just now was called ‘Sacrificing Clothes.’” Carl looked at his empty arm. “I suggest that from now on, whoever has the most free time should be the bait.”

"You're wearing too many layers, bring a couple more next time," Chen Hao said with a smile.

Nana turned on the lighting module, and light shone ahead. It was a huge cave with many stalactites hanging from the ceiling and the floor covered with slippery moss. It was quiet all around, except for the sound of water droplets falling from above.

"Thermal scanning complete," Nana said. "No signs of life within 50 meters ahead; the structure is stable."

“Finally, I can catch my breath.” Susan pulled out her notebook. “Those bats just now were very primitive in appearance, unlike modern species.”

“E-7 doesn’t seem to be the current standard either.” Chen Hao pulled out the metal plate. “Nobody on Earth uses this format to mark equipment.”

“There is no match in the database,” Nana confirmed. “But the material is a manganese-iron alloy, which was commonly used in industrial manufacturing in the mid-20th century.”

“That’s an antique,” ​​Carl said. “Could someone have actually been here?”

“Not only that,” Susan said, walking to the edge of the rock face. “Look at these scratches.”

Everyone gathered around. There was a set of regular lines on the stone surface, arranged in an orderly fashion, clearly not formed naturally. Some looked like numbers, others like symbols.

“This isn’t decoration,” Susan gestured with her hands. “It’s more like a marker, like the marks early humans carved in caves.”

“Who would keep records here?” Carl asked.

"Refugees?" Chen Hao guessed, "Or perhaps a lost expedition team?"

“They could also be prisoners,” Nana said. “Some civilizations have used enclosed spaces to detain dissidents, leaving them with traces as a means of psychological control.”

"Your imagination runs wild," Chen Hao patted her shoulder. "But I like it. The more outrageous it is, the more likely it is to be true."

They continued deeper. The passageway branched out more and more, each looking much the same. The ground was slippery, so they had to be careful where they stepped. Along the way, they found several more carvings, scattered in location but consistent in style.

“These symbols keep repeating,” Susan noted as she walked, “like some kind of route guide.”

“It might be a treasure map,” Chen Hao laughed. “The first clue: go through the bat nest; the second: avoid the gatekeeper monster; the third: find the glowing stone.”

"No light source has been detected so far," Nana said.

"Then you're glowing," Chen Hao said, pointing to her eyes. "Our team brings its own flashlights, it's worth it."

Nana didn't reply, but took a few steps forward and then suddenly stopped.

"etc."

She crouched down and pointed to a dent in the ground. Embedded there was half a broken piece of plastic, yellowish in color, with badly worn edges.

“This is a man-made object,” she said. “It’s made of polyethylene and its lifespan is estimated to be over eighty years.”

“More than eighty years ago?” Karl frowned. “Intercontinental travel wasn’t even a thing back then. Who would have gone to a deserted island like this?”

“Maybe it didn’t originate from Earth,” Chen Hao said.

"What do you mean?" Susan looked up.

"Did you forget the settings?" Chen Hao looked at Nana. "You said that some spaceships would deviate from their orbits during time jumps. Maybe these people fell from another era."

“Theoretically feasible.” Nana nodded. “If the warp drive malfunctions, it could cause the crew to travel to a non-target coordinate point.”

"So this place is a plane crash site?" Karl's voice trembled slightly.

“Not necessarily.” Chen Hao looked around. “It could be a temporary shelter. Look at these marks, they’re neat and orderly, not like something someone would scribble on before dying.”

“But they didn’t leave,” Susan said softly. “Otherwise, they wouldn’t have left without a trace.”

The temperature inside the cave gradually decreased. The air became thick and heavy, making it difficult to breathe. They came to a three-way intersection, with three passages symmetrically arranged, making it impossible to tell which one was the main path.

"Can we go back the way we came?" Karl asked.

“No.” Nana turned around. “The entrance has been covered by fungi. Those vine-like fungi grow extremely fast and sealed off the exit in less than half an hour.”

"So..." Susan looked at the three black holes, "we can only choose one path to take now?"

“And we don’t know which way leads to which way.” Karl kicked a pebble, which rolled into the middle path and was quickly swallowed by the darkness.

"I have an idea." Chen Hao took a coin out of his pocket. "Heads to the left, tails to the right, if it's on its edge, it goes in the middle."

"Are you serious?" Susan looked at him.

"What else?" Chen Hao spread his hands. "We can't exactly draw lots, can we? Besides, we don't have any paper."

He flicked the coin, and everyone watched it spin and fall.

It fell to the ground with a thud.

Chen Hao looked down and saw that the coin was stuck between two stones, standing upright.

"Hey," he grinned, "fate has put you in the middle."

"This is too much of a coincidence," Karl frowned.

“Unexpected events are the norm.” Chen Hao stepped forward. “The middle path might be the safest—after all, even a coin landed on its own.”

Nana walked at the front, the lighting module running continuously. The path ascended slightly, the slope gentle. After walking about a hundred meters, the carvings on the rock wall reappeared, this time more densely packed.

“These symbols have changed,” Susan suddenly said.

Everyone stop. The newly appearing lines are no longer simple symbols, but are arranged in an array, like some kind of code.

"Can you read it?" Chen Hao asked.

“It takes time to analyze.” Nana moved closer to observe, “but based on our initial assessment, this isn’t language; it’s more like a warning.”

"What warning?"

“I don’t know.” She reached out and touched the engraving. “But the last line… points downwards.”

Everyone looked in the direction she was pointing. There was a stone slab on the ground that was a different color and slightly flatter.

Chen Hao squatted down and pried at the edge with his hand. The stone slab was loose.

"Could there be something down there?" he said, forcefully lifting the lid.

Below was a shallow pit containing a metal plaque. The surface was severely corroded, but the words "**Do Not Open**" were still faintly visible.

On the back of the sign was a line of small, crooked characters:

“We’ve tried, and it’s still waiting.”

"Wait for what?" Karl's voice tightened.

No one answered.

A slight tremor suddenly came from the cave ceiling, and dust fell in rustling sounds. From the depths of the passage in the distance, a slow, steady footstep approached.

Chen Hao slowly closed the stone slab.