The old book Conan found had a worn cover and exuded an air of antiquity. He gently turned the pages; the text was ancient and obscure.

"What does it say on this?" Ran Mouri asked curiously as she leaned closer.

Conan frowned and examined it carefully: "It looks like some kind of code or secret code."

Ai Haibara took the book, studied it carefully for a while, and said, "Perhaps this is related to the secret of the castle."

Lin Yu said, "Then we need to crack it quickly."

They returned to their room with the book and began to work hard to unravel its mysteries.

After several days of effort, with Ai Haibara's help, they finally began to understand the contents of the book.

"This book seems to describe a mysterious place where a powerful treasure is hidden," Conan said.

Ran Mouri exclaimed in surprise, "Could this be the source of all the troubles that came with the castle?"

Conan nodded: "Very likely. And I have a feeling that this treasure could have a huge impact."

Just then, an uninvited guest arrived at the castle.

“I heard you’ve found an important book.” A mysterious figure dressed in a black robe appeared before them.

"Who are you?" Lin Yu asked warily.

The mysterious man smiled and said, "I'm here for that book. Give it to me."

Conan refused, saying, "Impossible. We don't know the truth behind this book yet."

The mysterious man's face darkened: "Then you've gotten yourselves into big trouble."

After saying that, the mysterious man turned and left.

Conan and the others felt that things were getting increasingly complicated, so they decided to speed up their research on the books.

They discovered that the mysterious place mentioned in the book was located in a remote valley.

"Should we go there and take a look?" Ran Mouri asked.

After thinking for a moment, Conan said, "Let's go. Maybe we can find the answers to all the questions there."

They prepared their gear and embarked on their journey to the valley.

Along the way, they encountered various severe weather conditions and difficult road conditions.

"This road is too difficult to walk on," Lin Yu complained.

But they did not back down and finally reached the entrance to the valley.

Thick fog filled the valley, obscuring the road ahead.

"Everyone be careful," Conan warned.

They proceeded cautiously, when suddenly they heard a strange sound.

"What is that sound?" Ran Mouri asked nervously.

Before they could react, a pack of ferocious beasts burst out of the fog.

"Run!" Conan shouted.

They fled desperately through the valley, with wild beasts in hot pursuit.

At the critical moment, Lin Yu used his high-tech equipment to create a disturbance, temporarily halting the beast's pursuit.

"We need to find that mysterious place quickly," Conan said with a serious expression. His intelligent eyes were fixed on the front, as if they could pierce through layers of fog and see directly where the target was.

Everyone nodded in agreement and quickened their pace to conduct a more thorough search. Time ticked by, and everyone's heart was in their throat. Just when they were almost in despair, someone suddenly shouted excitedly, "Look! There seems to be something over there!"

Following the direction the man was pointing, they could vaguely see a dark opening behind the mountain wall, almost imperceptible without careful observation. The group's spirits lifted, and they quickly walked towards it. Upon closer inspection, they discovered that it was actually a hidden cave.

“Perhaps this is the place we’re looking for,” Ai Haibara said softly. Her beautiful face was slightly pale with nervousness, but her eyes revealed a hint of anticipation and curiosity.

Conan cautiously approached the cave entrance and peered inside. The cave was pitch black, with only a faint light seeping in from the cracks above. A mysterious aura emanated from it, sending a chill down their spines. But they didn't back down; instead, they exchanged a glance, nodded, and resolutely stepped inside.

Upon entering the cave, the ground was uneven, and the surrounding stone walls were damp, with water droplets constantly dripping down. The air was filled with a damp, decaying smell, mixed with a faint fishy odor. The deeper they went, the stronger the mysterious atmosphere became, as if countless eyes were lurking in the darkness, watching them…