Rong Zhen and Lu Zheng carefully rushed to Shili Slope, and indeed found many soldiers coming and going there, and the guards were extremely strict. It seemed that they were right, the King of Wei's gunpowder depot was in this place, but how to blow up the gunpowder depot without being noticed by so many soldiers was a big problem.

Fearing that they would be discovered, Rong Zhen did not let Lu Zheng approach, but asked him to wait for him at a place not far from Shili Slope, and he went to investigate. When he came back, Lu Zheng could not wait to ask, "How is it?"

Rong Zhen nodded, "My guess is correct." Lu Zheng

breathed a sigh of relief. It was really that Rong Zhen's move was too risky. If they guessed wrong, they would be trapped.

Rong Zhen's face was still not very good. He did consider that the King of Wei would strictly guard the gunpowder depot, but he never thought that there would be so many guards. It seems that Jian Yu's bombing of the Jie people's gunpowder depot made the King of Wei very vigilant, so he sent more troops.

Lu Zheng asked about the situation and fell into deep thought. The gunpowder

depot of the King of Wei was located in a valley. Not only was there a lot of guards in the valley, but there were also archers on both sides of the valley. They could not get close to the valley, let alone destroy the gunpowder depot.

The oil in Lu Zheng's hand could make about ten simple bombs, but if these simple bombs did not hit the gunpowder depot directly, they would be useless and would expose their position. It was a loss.

Rong Zhen knew that he had misjudged this matter, but in fact, when he thought of this idea, he had already had the worst plan. He knew that if the gunpowder depot could not be destroyed, even if Su Dai led the army into Yanjing, he would only fail in the end. He could certainly let Song Zhiyi or Nie Zhishu do this. He believed that with their loyalty, they would not hesitate even if they knew that they would die.

But he did not make such a decision.

Rong Zhen's mentor once told him that those who truly accomplished great things could never be soft-hearted. He was ruthless to his enemies and even more ruthless to himself. Over the years, Rong Zhen always thought that he had done a good job, but in fact, he was still the little bully who wandered around Yanjing at the age of fifteen with chivalry.

Having figured this out, Rong Zhen calmed down and his thoughts became clear. Many things that he had not thought of before also emerged in his mind one by one.

Was the reason why the King of Wei set up the gunpowder depot in Shilipo really just the reason on the surface? If not, would he have used this entire gunpowder depot as a trap?

Ye Wenguan saved them, so why did he suddenly chase them away?

Also, the bits and pieces of information he had obtained about the truth of the past over the years, was it someone who deliberately leaked the clues and led him step by step to the present?

Rong Zhen knew that he could only ask the King of Wei or go to the underground to find Emperor Yongning to know the truth.

Now that he had figured it out, Rong Zhen did not intend to sit and wait for death. Since the King of Wei dared to use such a big hand to set a trap, he would let him lose more than he gained. Rong Zhen glanced at Lu Zheng beside him, with nostalgia and struggle in his eyes. He didn't know how to say goodbye to Lu Zheng. He was afraid that if he knew, he would follow him regardless of life and death...

Rong Zhen thought so, using his hand as a knife, raised it and was about to chop at the back of Lu Zheng's neck.

Lu Zheng was unaware, but just as Rong Zhen's hand was about to touch his neck, he suddenly shouted: "There is a way!"

Rong Zhen hurriedly retracted his hand, and the force that was removed was all transmitted back to his body, which made him unstable for a moment and took two steps back.

Lu Zheng didn't care about these, and still said excitedly: "I thought of it, we can use hot air balloons!" He thought Rong Zhen didn't understand, and quickly changed his words, "It's Kongming lanterns!"

Rong Zhen frowned: "Kongming lanterns have always been used to send distress messages when the city is besieged, how can they send simple bombs into the valley?"

Zhuge Liang invented the Kongming lantern for the purpose of calling for help during the siege. Later, the principle of the Kongming lantern was known to the public, and the military effect was not so strong. Only some businesses used it to attract children or lovers during festivals. Kongming lanterns usually use candles as fuel, so the outer shell can only be made of very light objects such as bamboo strips and paper, otherwise it cannot be launched.

Lu Zheng knew Rong Zhen's worries and said quickly, "But we have oil!" In fact, in modern times, the development of hot air balloons has been very mature. Helium is generally used as fuel, but now they don't have such conditions at all, so they can only use oil instead. Anyway, Lu Zheng doesn't plan to sit on it himself.

After Lu Zheng explained the principle, Rong Zhen understood it, but he still shook his head and said, "Even if you can make what you call a hot air balloon, how can you guarantee that it will definitely fly to where you need it to go, and how can you ensure that a simple bomb can be ignited in the air?"

Lu Zheng has already thought of these, thanks to the science he learned in high school, and thanks to him for not returning all the physics knowledge to the teacher. If you want to get the hot air balloon to the right position, you need to calculate the wind speed and the speed at which the oil burns. He picked up a branch and muttered to himself as he calculated on the ground. Fortunately, when he brought the crude oil to the border town, he used his remaining chemical knowledge to desulfurize and remove impurities from the crude oil, and also calculated the burning speed of the crude oil. Now, according to the wind speed and the resistance caused by the size of the hot air balloon, and the appropriate wind direction, the hot air balloon can be roughly sent to the right place. Fortunately, there is no need for precise strikes. As long as the simple bomb can land above the gunpowder depot, a chain reaction can be generated.

As for the method of making a simple bomb, Lu Zheng put all the materials into a bamboo tube, stuffed it tightly with a plug, leaving only a fuse tied to the bamboo tube, and then coated the bamboo tube and the fuse with white phosphorus. When the fuel of the hot air balloon was ignited, the heat generated by the friction of the atmosphere during the rapid fall of the bamboo tube was enough to ignite the white phosphorus.

Lu Zheng had already prepared the materials for making a simple bomb, and now they were all ready to go, except for the white phosphorus. Fortunately, both of them brought a fire starter with white phosphorus in it, which was enough to be used only on the fuse.

In fact, they had no other choice at the moment. Rong Zhen could only trust Lu Zheng. Moreover, since they met, Lu Zheng had brought him enough surprises. In addition, this matter sounded very feasible, so he agreed.

The weather was still a little hot, and the most suitable time was actually in the evening. The two of them were lucky. Recently, there has been a south wind blowing, and the direction happened to be towards the valley at Shilipo.

The two did not delay any longer and used cloth and leather to make simple hot air balloons. Although the final product looked very shabby, after Lu Zheng's test, there was no big problem.

Now they just had to wait for the evening.

The waiting time was a bit long. Rong Zhen checked the hot air balloon again. Lu Zheng was still worried and checked it again. It was finally evening. The summer evening was a bit dark. The setting sun hung on the top of the mountain and was reluctant to set. A slightly warm wind blew in the air, as if it wanted to take away the dryness and heat.

Lu Zheng and Rong Zhen came to a high ground. From here, they could see that the valley was silent, but weapons and low voices could be heard. Because there was a gunpowder depot in the valley, there was no fire. Only soldiers holding torches walked around on both sides of the valley to prevent night attacks.

Lu Zheng was holding a hot air balloon that had been made and tied with a simple bomb. His hands were shaking and his heart was beating wildly. He knew that this was their only chance. If they couldn't destroy the gunpowder depot, he and Rong Zhen would probably die. So even though he knew that there were lives in the valley, he could only force himself to be cruel. He was only worried about whether this hot air balloon could complete the mission. After all, he only had theories and had never put it into practice.

Lu Zheng placed a warm palm on the back of his cold hand, and Rong Zhen's firm voice rang in his ears: "Don't be afraid, believe in yourself, and believe in me."

His voice was as steady and powerful as ever, as if they were not taking a risky gamble, but a battle that was sure to win. Lu Zheng's heart suddenly settled. He did not look back at Rong Zhen, but carefully applied white phosphorus on and around the fuse, and then ignited the fuel under the hot air balloon.

As the bright flame illuminated Lu Zheng and Rong Zhen's face behind him, the airbag continued to expand, and finally with a light push from Lu Zheng, it swayed towards the direction of the valley.

Lu Zheng watched the hot air balloon nervously as it got closer and closer to its destination, his heart almost jumping out of his throat. It was not known whether it was because the wind was too strong or because too much fuel was added, but the hot air balloon continued to fly forward when it reached the top of the valley, and finally flew directly over the valley.

A bad start!

Lu Zheng's heart was lifted up again. Because of the limited materials and the fact that oil had to be used as fuel in addition to making simple bombs, they did not make many hot air balloons, but only three. And now that the first opportunity has failed, if the next hot air balloon fails, I'm afraid the matter will be in suspense.

Lu Zheng calmed himself down, carefully measured the wind speed again, and then scooped out some of the fuel for the second hot air balloon. Fearing that there would be no wind in a while, he did not dare to dawdle any longer, and repeated the first step, sending the hot air balloon into the sky again.

As the hot air balloon approached the destination, Lu Zheng's heart became more and more nervous. His hand was only held in the palm of Rong Zhen's hand. He could feel Rong Zhen's comfort, but this made him more eager to succeed this time.

I don't know if God really heard Lu Zheng's voice or his half-baked knowledge of physics played a role. This time, when the hot air balloon flew to the top of the valley, the flame suddenly flashed and went out. Without power, the simple bomb fell rapidly downward.

Because it was dark, Lu Zheng couldn't see the falling process of the simple bomb, but he saw a flash of fire in the air, and then a huge fireball exploded above the valley. The scattered sparks and oil instantly ignited the entire valley. For a moment, the valley was full of people and panic.

The flames quickly rose high. From where they were, they could hear the faint voices of people shouting for help from below. It was too late. With a loud noise, the valley was like an earthquake. There were loud noises and screams one after another. Against the backdrop of the raging fire, it was like hell.

Lu Zheng was so excited that he couldn't help but turn around and hug Rong Zhen: "We succeeded!"

Rong Zhen also smiled gently. He put his arms around Lu Zheng, who was too excited, to prevent him from falling off the cliff. He had never thought that Lu Zheng could actually succeed. This little guy always seemed to appear in the most desperate places and bring him hope.

Just when the two were immersed in joy, Rong Zhen's face suddenly changed, and he rolled to the side while holding Lu Zheng.

There were only a few "swoosh" sounds, and several sharp arrows were inserted into the place where they were standing before. Rong Zhen's beloved horse did not dodge in time and was pierced directly in the belly by an arrow. It hissed and fell to the ground.

Rong Zhen held Lu Zheng behind him and looked at the place where the sharp arrows came from. A figure slowly walked out.

"Han Zhu!"