(Thanks to "Beginning Le" and "Book Friends 20170804205809025" for their rewards)

The setting sun faded under the winding curves of the cyan ridge, and the bright color outside the office window was slowly blurred by gray, and the wind blew through the plane trees outside the window, making a faint rustling sound. The sky was dark, and in the old office building composed of gray wall tiles and pointed eaves in the sycamore forest, only the third office on the left side of the second floor was still lit with white lights, like a lonely ship in the rough waves of the night.

No one spoke in the office, five people fanned around behind the desk, Xiao Zhang, who was sitting in a chair and wearing a security uniform, was looking at his phone, while the five people behind him were staring at the very monotonous black and white picture on the monitor with different expressions.

No one spoke, and the air was eerily quiet.

After listening to Director Wu's introduction, Yan Yitong felt that the black and white classroom on the monitor was a little infiltrating, and outside the dark glass window, it seemed that something scary would come out at any time, such as a bloody palm print, a rotten face, or a pair of black hole-like eyes like the white-skinned child in "The Grudge......

Yan Yitong couldn't help but approach Cheng Mo tightly, and quietly grabbed the sleeve of Cheng Mo's shirt with one hand.

Fu Yuanzhuo's expression was also a little nervous, and he couldn't help but ask in a low voice: "Director Wu, no.... Something strange is happening, right?"

"The strange thing is that nothing strange happens....." Director Wu said in his neutral voice, and suddenly the terrifying atmosphere in the office disappeared.

"You mean those paintings just appeared out of thin air?" Fu Yuanzhuo asked.

Director Wu nodded, "It can be understood in this way, my colleagues and I have studied it many times, and those paintings really seem to have appeared out of thin air!"

Fu Yuanzhuo didn't ask, and looked at the picture taken by the monitor intently, but .....

But it's boring and makes people doze off.

After watching the picture that seemed to be frozen for more than an hour, except for Cheng Mo and Shen Youyi, everyone's spirit was a little tired, and Yan Yitong, who was still a little scared at the beginning, was a little confused at the moment, covering her mouth and yawning, if she was sitting at the moment, I am afraid she would have fallen asleep a long time ago.

As for Fu Yuanzhuo, he looked at the screen motionless with his spirit, and at first he listened to what Wu Li said so magically, Fu Yuanzhuo was still very interested, but after watching the whole video, it was not the same thing at all, there was no movement in the classroom under the monitor, until the east was white, and the server of the school monitoring system was restarted, and the picture did not even shake.

There is no scary background music, no white shadows that suddenly drift by, and no hideous faces that dominate the whole picture.....

This made Fu Yuanzhuo even want to have something scary to refresh his mind, Fu Yuanzhuo glanced at Cheng Mo, he was still as serious as he was at the beginning.

At this time, after watching the three videos half-delayed and half-fast-forwarded, Wu Li broke the silence and said with a serious expression: "Xiao Zhang, just put the last one, and then drag it until five o'clock in the morning!"

Xiao Zhang, who was playing with his mobile phone, said "oh", put down his phone, clicked on the last video numbered "2018619", and directly dragged the long progress bar to the end of the time, which was very accurate and stuck at 4:59, obviously this video has been studied many times by the people of the Ministry of Security.

"This is the video from June 19th, the date of the last mysterious chalk drawing in the classroom of the first (9th) class of high school last semester, plus the previous nine times, for a total of exactly ten times..... If you count the appearance in the classroom of the second (9th) class of high school this Monday, it will be a total of eleven times....." Director Wu quickly and clearly stated the number of times the chalk drawings appeared.

"Huh?" Shen Youyi was a little surprised, "I haven't seen any chalk drawings this week!"

Cheng Mo's eyes stared at the monitor without moving, and said lightly: "I wiped it off." ”

Shen Youyi, who was beside Cheng Mo, turned his head to look at Cheng Mo's side face, his voice relaxed, and he smiled slightly: "So that's the case! Thank you, Cheng Mo....."

"I happened to be on duty that day. Cheng Mo replied expressionlessly.

Director Wu, who was standing at the window, also turned his head to look at Cheng Mo, he still had great hopes for this young man with a bit of unbelievable observation, so he asked, "Cheng Mo, I watched several videos, did you observe anything?"

At this time, everyone turned their eyes to Cheng Mo, including the young man who was absentmindedly playing with his mobile phone, and they all looked back at Cheng Mo, who was not amazing.

Cheng Mo looked at the monitor intently, and shook his head silently as if he didn't care about Director Wu's inquiry.

Director Wu sighed softly and said to Xiao Chen, "Come forward!"

It seemed that Director Wu was a little disappointed, so the atmosphere of the whole office became dull like the night outside the window after this soft sigh.

When the outside of the classroom in the monitor was white, the picture finally appeared color, but the color was not strong, Cheng Mo looked at the empty classroom, and the empty blackboard, and then the video went black, and when the video was lit again, the time in the upper right corner had come to 5:45, and the chalk drawing with the theme of Teacher Shen appeared on the blackboard that he had also seen.

"Do you want to see anything else?" asked Director Wu.

Cheng Mo opened his mouth and said, "No need for the time being, Director Wu, I have a few questions I want to ask, can you help answer them?"

You ask. Director Wu said.

"Does the server of the school surveillance system shut down at half past five every day and then restart a quarter of an hour later?"

Director Wu nodded, "Yes." ”

"So have you tried to change the time of restarting the server to catch the perpetrator?" asked Cheng Mo.

"Of course I tried, because the other party only appeared on weekends, so several times on Monday mornings, we didn't restart the server, but nothing was taken.... The other party seems to have calculated correctly, as long as we don't close the server, he won't show up....." Director Wu replied with a frown.

"Hackers?" Fu Yuanzhuo said with a flash of inspiration.

"We also had such suspicions, but we invited professionals to check and found no problems, and in addition, our monitoring system is not actually linked to the network, and it is .....unlikely that we will control our monitoring system without entering our computer room," said Director Wu.

"Isn't the solution to the problem very simple? As long as you don't restart the server in the early morning, or simply change the time, restart the server in the middle of the night every day, or even don't restart it every Monday, won't the other party appear?" Fu Yuanzhuo said.

Director Wu shook his head and said: "That's not admitting defeat to the perpetrators, not to mention that the restart is inevitable, we can only change the restart time, we have tried this, and for a while we all restarted at three o'clock in the morning.... As a result, one day, when I opened the monitor, I saw chalk drawings on the blackboard..... Actually, it's not impossible for us to not restart the server every Monday, but can you guarantee that the other party won't change the time and let the chalk drawings appear every Tuesday?"

Fu Yuanzhuo was speechless for a while, swallowed a mouthful of saliva, hesitated for a moment and said, "This ..... It's obviously an insider's trick, isn't it?"

"Don't talk about you, I thought so at the time, so we launched a self-examination within our security department! However, all the personnel of our security department did not have time to commit crimes...."Director Wu said.

Fu Yuanzhuo was puzzled, so he could only turn his head to look at Cheng Mo, "Cheng Mo, didn't you find a clue?"

Cheng Mo pushed the glasses on the bridge of his nose, "I just think it's strange, why chalk drawings have to appear after the server is turned off!"

"Of course, I'm afraid of being photographed by the surveillance! Only these fifteen minutes can be used to get the painting on the blackboard!" Fu Yuanzhuo said as a matter of course.

"But fifteen minutes is definitely not enough for him to complete such a large chalk .....," Cheng Mo said with a frown.

"That's the most amazing part..... I asked someone who had studied drawing to give it a try, and it would take at least one to two hours to finish the work that the perpetrator had drawn..... That's why I say these chalk drawings come out of nowhere....."

"It's not completely impossible, is it? For example, several people painted it together!" Fu Yuanzhuo said.

"It's not out of the question, but I don't think it's going to be a few people. Director Wu thought for a moment and replied.

Cheng Mo shook his head, "It must have been done by one person...... It's a lot of fun..... It's similar to reasoning about the case in the secret room..... It's just that the content of the case has changed from how the murderer killed the victim to how the perpetrator completed the painting in the secret room..."