They came to the playground and followed Gao Caiqin's instructions to a fence. Inside and outside the fence are lush camphor trees, which open their umbrella-like canopies to block out all prying eyes.

They looked around the area, and at first glance they didn't find anything out of the ordinary. The fence is three meters high, and if you add the electronic fence above, the height increases again. If you want to climb the wall from here, not to mention the little junior high school students, it will be difficult for even those well-trained athletes or parkour masters.

The gap between each railing is only a dozen centimeters, and even a child of several years old is unlikely to pass through it.

Ling Ling pushed each railing one by one, although the school has been built for a long time, and the infrastructure is a little old, but these iron generals have been stationed here for decades, guarding this side of the world without moving.

Heaven does not go to the ground. But the ground is also solid and firm, without any flaws.

Ling Ling walked around this small place, but still didn't find anything, and finally patted the wall in discouragement and asked Gao Caiqin: "Can you recognize which people were sneaking around here that night, and can you recognize their voices?" I'll just catch them and show them to us, so we don't have to look here like headless flies. ”

At this moment, there was a sudden sound of metal turning "Click-"

Looking at it again, Wen Qiao already had a dismounted iron railing in his hand.

"This ......" Ling Ling's eyes widened, "How did you do it?" ”

"Look at the connection points." Wen Qiao used his slender hand to signal her to look at a place: "The joints of the other railings have electric welding joints, which are fixed on the horizontal railing below, only this one does not have them." ”

"But I've tried every one of them just now, and I can't pull them out." Ling Ling still couldn't believe it.

"In ancient China, there was a way of building called mortise and tenon, did you know?"

Ling Ling nodded: "I've heard of it." ”

"In a mortise and tenon structure, the protruding part is the tenon and the recessed part is the tenon. The convex and recesses combine with each other to hold the furniture or building in place without the use of any nails. The intricately designed mortise and tenon structure is tightly fastened to the point where it is even seamless. ”

"However, the traditional mortise and tenon structure is applied to wooden buildings, and many retro wooden furniture nowadays also deliberately pursue this antique effect, but it is also the first time I have seen it applied to metal structures." Wen Qiao said.

Ling Ling followed his introduction to look at the joints of the iron railings, and sure enough, there was something unusual.

The balustrade was a slender column, and the connection and fixing place should also be round, but under this particular balustrade there was a small square protrusion, and the place where it was connected and fixed was a "convex" notch.

"This is a structure in mortise and tenon joints called a horse pin. To splice, put the tenon into this slightly larger notch, then push it forward and snap into the smaller notch. In this way, after the tenon and tenon are combined, they will not come out of it regardless of lifting or hanging. ”

Ling Ling exclaimed, "You even know this!" Curiously, he followed the method he said, and operated it with his own hands, and sure enough, he was able to reinstall the railing, and no matter how much he shook it, he could not move at all. Unless you know how to do it, it's impossible for anyone to see the doorway.

Gao Caiqin was also interested, and dismantled it in the opposite direction. At this time, the gap that was originally only a dozen centimeters has expanded to thirty centimeters, and as long as you are not too fat, I believe you can drill out of this gap.

Ling Ling suddenly thought of something and exclaimed, "That's not right! Even if Lin Xuerou knew that there was a secret passage here, why did she come here? It was supposed to be a weekend off, and if she wanted to sneak into school, it would be reasonable, but if she wanted to go out, she would just walk through the gate openly, and no one would stop her! ”

Wen Qiao heard her words, and his eyes revealed a glint of approval: "The child can be taught." ”

Ling Ling's heart moved, and when he heard his sudden praise, his cheeks immediately flushed slightly.

Looking through the gap here, there is still a green forest outside. Camphor is the most common greening tree in the city, they are evergreen all year round, forever stretching their soft and dense foliage, like strings of wind chimes, rustling when the wind passes, and like a pair of scissors, when the sun is shining, they are cut into pieces. They are a secluded and independent place in the noisy city, standing in their arms, there is coolness in the scorching heat, and shelter in the cold wind.

After passing through this green forest, there is a river about 10 meters long, and across the bridge is a bustling business district.

"So, if Lin Xuerou also knew that there was a secret passage to enter and exit the school, then, it was likely that she didn't come here that day to get out, but to ......" Wen Qiao said this, stopping the conversation.

Outside the fence is dirt floor, although it hasn't rained in recent times, and the ground is dry and hard, leaving no visible traces. Wen Qiao still leaned down to observe carefully, and after a long time, he pointed to a trace on the ground and said, "Look." ”

Ling Ling tilted his head and looked at it for a long time, but he didn't see anything famous: "What is this?" ”

"It should be a shoe print on the forefoot. The forefoot part of this footprint is focused on the force and has a tendency to push backwards, so it leaves such a shallow arc on the ground that is not easy to leave marks. Wen Qiao replied.

"If you look at the position of the tip of the shoe, combined with the traces I just mentioned, you can simulate the direction of this person's footprint."

"What do you mean...... Someone coming in from here? Ling Ling was not stupid, and after his click, he immediately understood what he meant.

"Not many people know about this secret passage, otherwise it wouldn't have been designed to be so hidden. Therefore, this trace should be recent. Maybe it was left by Lin Xuerou when she came here that day and opened the door to let people in. Wen Qiao concluded.

Although his reasoning was reasonable, Ling Ling was still a little unacceptable, because it meant that their investigation had gone in the wrong direction two days ago. They spent a lot of energy investigating the surveillance cameras around the school, wanting to know which direction Lin Xuerou went after leaving the school. Visits were also made to the surrounding area, hoping to find witnesses who could provide them with clues. But in the end, Lin Xuerou may not have been out of school at all.

Ling Ling still wanted to die and struggle: "Maybe Lin Xuerou went out from here, maybe these little girls like to take some unusual roads." You tell me? She suddenly asked Gao Caiqin, wanting to understand the real thoughts of little girls of their age from the mouth of this little girl.

But at this time, Wen Qiao looked at her with a strange look.

Ling Ling was stared at by him uncomfortably: "Why are you looking at me like this?" ”

"You two are really brother and sister, and you all have the same problems."

"What?" Ling Ling didn't understand the meaning of his words, but at least he knew that it was not a good thing.

Wen Qiao didn't answer her, but asked directly: "Has it been checked in the school?" ”。

"School? We asked her teachers and classmates, and we also looked for the dormitory, canteen, and other places that might appear, but she was nowhere to be seen. If it appeared somewhere else, someone would have seen it and reported it to us...... "Ling Ling tried her best to make amends, they really didn't conduct a thorough search of the school, but took it for granted that Lin Xuerou had run away from home, no matter how bad it was, she was tricked, kidnapped or something worse, in short, she must have gone to some unknown place, but no one thought that she might not have left the school at all.

"Then hurry up and investigate." Wen Qiao unceremoniously threw down this sentence. "Only action can validate your ideas."