"Let's hurry on," Said William. So he pulled out his computer, opened the map, and saw the following route.

Connor had arrived at Woodford Refitting Factory. The party crossed a gentle slope, in front of which was Checkpoint 23. They collected another 1.5% of their energy. A path of glowing mushrooms, like the one in Butterfly Castle, winded its way across a vast purple plain. The party followed its directions, quickening their pace to keep up with William. Natalie enjoyed the dreamy glow of the mushrooms under the tires.

Gradually the landscape changed. The violets and lavender still lined up neatly on either side, but they could already see a wide river a few kilometers away. As they continued to approach and finally reached the river, William was able to watch carefully. The river was crystal clear, like emeralds falling from the sky. The surface of the river was faintly wavy, reflecting the afterglow of two falling mother stars. There were some fishes in the water playing happily, while at the shore occasionally stopped a few water birds foraging. Some of the low grass was growing along the banks of the river, as if to tell the planet that they were unimaginably hardy.

William and Ranran had never seen anything like this. This would have been unbelievable on Earth a few decades ago.

"Master, it's getting late. I think we should ask the residents to find a suitable place to rest." Photon walked up to William, yawning. He nodded his head in agreement.

Ranran saw a wooden sign standing there. It read,

Welcome to Lavender River Valley! If you want to find a hotel, cross the bridge, turn left, then turn right at the fountain. You'll see a green door. There it is.

So they followed the instructions of the sign and found Lavender River Valley Inn. At the door, an old man stopped them. "Are you guys going to the flying endurance championship?" He asked.

"What makes you think so?" Ranran asked in surprise.

"I'm a fan of her." The old man said as he walked slowly up to Rebecca, "I think you've come to the right place, because here is a retired champion plane. If you have any questions about the race, you can go to him."

"Wow!" Rebecca exclaimed.

The old man said kindly, "Let me find you a room first. I'll send someone up to your room later to tell you how to find the plane." And he went into a little door. A few minutes later he came out, holding a mushroom-shaped number plate with the number 413.

"See that little building covered in lavender?" He pointed to a low building a few hundred meters away, "Go to the fourth floor. You'll find it soon enough."

"Thanks for the tip!" William said goodbye to the old man and led the others to the room. It was a good thing that he had paid attention, or he wouldn't have noticed the shamrock icon on the old man's chest. "Why does this icon look so familiar?" He said to himself.

Room 413 really stood out. William brushed the number plate in front of the lock and the door opened automatically. Then the party went in.

The room was scented with lavender, very much like that castle. Three huge soft beds stood on the floor. At once, William, a little tired, threw himself on one of the beds and looked up at the beautiful pictures on the ceiling. It was about Lavender River Valley. Somehow, the picture he was looking at began to move. The river began to flow slowly, with a clear sound. The lavender was dancing happily in the breeze. He could also see two shining mother stars, singing birds, and a lot of other obscure things. They were all dancing happily.

The others, too, gaped at the ceiling. Then a voice behind them explained the scene,

"Do you think it's incredible? The ceiling is actually a screen."

William sat up and looked with the others in the direction of the voice. They found a beautiful girl standing at the porch. Under the red scarf she wore, her dark curls showed, and her bright black eyes were as kind as the old man had been. Two mother stars threw the last rays of the day over her blue cloak, and star-shaped diamonds sparkled at her waist. She had the same icon on her chest as the old man. Smiling, she walked up to William and took off her scarf, revealing all her curls.

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"My name is Sierra." She said, "I guess you met the old man just now."

"Yes," William replied, "I'm William and this is Rebecca. She's going to race."

"Wow, Rebecca! I'm a fan of yours too! I've heard so much about you and I was not able to see you until today!" Sierra immediately turned to Rebecca and gave her a look of admiration. "Oh, don't bother." Replied Rebecca shyly.

"I was sent by the old man to tell you how to find the retired champion plane." Sierra told everyone, "I am his granddaughter and the owner of that plane. I've won most of the championships with the plane, but a few of the wins were his own -- er, I mean, he didn't ask me to drive him. He finished the race by himself."

William admired her. "Did your grandfather enjoy watching the endurance championship, too?" Ranran asked.

"Yes. Like me and my father, he dreamed of flying high in the sky. But in his childhood, due to inferior conditions, he could not fulfill his dream. So my father began to work hard for his dream. Luckily, he was ready to enter for the flying endurance championship, so after a lot of practice, he won his first championship. And what accompanied him to usher a successful start is the plane that accompanied me."

"Oh, so this plane is also an old hand." Photon said to Natalie.

"That's right. My father retired after seven championships and now works in an airplane refitting factory --"

"Wait a minute." Photon interrupted Sierra, "Is his refitting factory Woodford Refitting Factory?"

"Right there." Sierra replied, "Why, how did you know it? By the shamrock icon on our chests?"

William shouted, "Oh! I see! No wonder I see it in all three of you. This is the symbol of family!"

"Uh, yes." Sierra laughed, "All of our family members wear it."

Rebecca added, "Your father refitted me." Then Sierra understood.

At this time outside the window, the earth had been covered by night. The stars were shining, the crickets were singing, while the rivers were flowing quietly. The perfumes of violets and lavender were undiminished. In the distant towns, lights were blazing everywhere, and the streets were still bustling. But here in the quiet Lavender River Valley, everything was quiet.

"You must be tired." Sierra said, "Go to sleep quickly. As for finding my plane, I'll take you there tomorrow."

The party then arranged the packing, settled their own positions, and prepared to enter the land of sleep. Sierra was already in bed, but William sat up and said to her, "Sorry to bother you, but I want to talk to you about Rebecca."

Sierra lowered her voice, "Go ahead."

"OK. When we were on our way, Rebecca trained really hard. What you don't know is that Rebecca has won the champion many times in tryouts, but due to the bugs in the race rules, the new opponents became more powerful, and she once fell into depression and put herself under house arrest. Fortunately, we came to re-light the flame of her dream and faith."

"Ah, I see." Sierra's eyes gleamed faintly in the darkness.

"We put her through a lot of training and we just finished training before we got here. She hasn't been slacking off, practicing with all her might and striving for excellence. At least we feel she's regained her former mastery, but I'd like to trouble your plane to check it again tomorrow, OK?"

"That's certainly no problem."

"Thank you very much indeed. And I've just learned that your father works in an airplane refitting factory, so I'm curious to know what you want to be when you grow up."

Sierra was silent for a moment, then replied, "I think I might be able to study new technologies related to airplanes."

"Oh? That's great. What's it about?"

"I don't know if you've heard of the camel scientist."

"Yes, and we have seen him."

"That's good. I've heard that he's recently been working on how to use small fusion cells to power ion engines, and has announced that the technology will soon be available for commercial use."

William nodded and told the girl that Rebecca had one of this kind of batteries on her body. Sierra was surprised and delighted. "No wonder you keep saying her work is excellent! I think she's going to do really well with this battery." She said excitedly.

"But it's not clear to me why you would use this type of battery to drive an engine." Said William, puzzled.

"I think it's a good fit for ion engines." Sierra explained, "You may not know this, but ion engines have been in use for more than 30 years. However, due to a number of shortcomings -- mainly low specific energy of battery -- they have never been used on a large scale. As a result, most of the aero-engines we use now are still composed of a few piston engines and a majority of turboprop and turbofan engines. Of course, electrified power modules are also common, but for now they must be used with propellers. However, if there is breakthrough about this kind of battery technology, the ion engines will undoubtedly be widely used, because they have a higher specific energy than any chemical battery, meaning they can be lighter, smaller and more powerful. Ion engines use a lot of power, so specific energy is the biggest problem. I think I can continue to optimize this technology, such as how to reduce the size of the engine and improve its efficiency. This would allow airplanes equipped with such engines to reach the same speed as, or even exceed, those equipped with turbofan engines. If the technology is mature enough, it could be used in flying endurance championship decades from now."

William listened carefully to these words. "That's a nice dream." He praised, "And it's good to have dreams."

"Yes," Replied the girl, "since we are here in the universe, let life shine with its brightest light. Oh, you're all tired. Do you have anything else to tell me?"

William shook his head. "Rest quickly, then. I'll rest with you and take you to find my plane in the morning." Sierra said.

In a few minutes all was silent except for the faint snoring of the sleeping party.