On the hillside, several shadows were racing with the liquid. They screamed bitterly, afraid that the acid behind them would give them the kiss of death. After the introduction of the little robot, it was clear to William that the sooner they could, the better.

Fortunately, they were just in time to reach the open ocean ahead. Barely a second later, the first fluoroantimonic acid molecule rushed into the water's embrace. Then the fluoroantimonic acid flowed into the sea. The water boiled immediately and it took it about ten minutes to cool down.

"Oh, it scared me to death." Ranran wiped the cold sweat on her head and said breathlessly.

Then the party, submerged in the sea, saw a huge, glowing yellow object descend slowly from overhead. Only a few minutes ago, it was about a few kilometers high in the air; now it was settling squarely on the sea in front of them. The whole party swam over and looked at the strange object. It looked like a jack-o'-lantern, with a circle shape of a pumpkin, a ghost-like smiling face and a glowing body. However, this object was definitely not a real jack-o'-lantern, because whether objects would float depended only on their relative density to the atmosphere, other than any other parameter. The little robots had already detected that the planet's atmosphere was not dense enough to keep pumpkins suspended in the air.

"So what on earth is this?" William said to himself. As he was thinking, the jack-o'-lantern's upturned mouth opened. It was actually a door. A sphere fighter poked its head out of it.

William was ecstatic, so he put all his strength on the jack-o'-lantern. Soon everyone was inside.

Checkpoint 37 is cleared. Energy charge: 2.5%.

White sphere fighters surrounded them with joy. They jumped up and down happily. "It's good to see you again!" Exclaimed Ranran, "We are very worried about your safety."

"Actually, your comrades have already shot down the bomber." A voice came from behind the sphere fighters. Almost the next second, a staggering old man appeared in front of the party. He looked kindly at the aliens with clear blue eyes, his pale hair fluttering slightly. His face was covered with gully-like furrows. The old man slowly and gently stroked a sphere fighter next to him with one hand, while in the other hand he held a mouth organ.

"Oh?" William thought, "This man looks familiar, but I can't remember who ever mentioned him."

Then the old man took out a photograph and handed it to William. "Come in and have a rest, friends. But I suppose you've seen this man." He said, smiling.

William caught a glimpse of the figure in the photo as a skeleton playing an organ. "Isn't that the skeleton organist?" He said to himself, "Why does the old man have a picture of him?"

Although the old man was nearly a centenarian, his hearing was still very keen. Hearing William's question, he replied,

"On the back is the answer."

On the back of the photo was printed in large letters: HANDEL.

"Wow! So you are 'Mr Handel' as the skeleton organist calls you?" Natalie asked, surprised and delighted.

"Yes, I am Handel, the music teacher of the skeleton organist. But I guess he only told you about my experience and didn't tell you anything else."

"Yes." Aria replied, "So it's a great honor to meet you."

"There's one very strange thing, Mr Handel -- oh no, two things." Rebecca cleared her throat and turned to Handel, "The skeleton organist told us he found you in the daytime hemisphere, but why are you now in the nighttime hemisphere? In addition, according to his descriptions, you are an extremely good musician, but for me, that's not what musicians look like when they appear. So what is this jack-o'-lantern you are taking?"

Handel did not answer at once. Instead, he had the others sit on a sofa in the corner. "I'm sorry I kept you standing." He said with a guilty smile, "And that has something to do with these strong and reliable partners of you." He patted the sphere fighter parked in front of him.

"Yes, I am a teacher as well as a musician, but I don't think I am good enough to be called good. I was only doing my best as a music teacher, so I was surprised that the skeleton organist should be so grateful.

"I retired early and dreamed of spending the rest of my life in peace. Lately, however, something strange has been happening in the daytime hemisphere. For example, there are some scary, devil-like trees. Another example is that crows often fly over people's heads. What is most puzzling is that there should be the roar of engines in the air, which does not sound like any commercial engine."

Hearing this, William began to tremble. "We've all met those before." His voice trembled uncontrollably.

"Yes, I'll say that soon. Some of the inhabitants that live at the nighttime hemisphere also reported these strange things. They said it terrified them so much that they were afraid to go out. So a company that makes airships made the 'aerogel jack-o-lantern airship' and looked for volunteers who want to take it to the nighttime hemisphere to find out why. But that's not how they advertised it -- their slogan was, 'Go around the planet with this edged tool!'

"Not many of the residents have the desire to travel around the planet, and with these strange things going on, even fewer wanted to sign up. I clearly remember that only five volunteers went to the headquarters of the company, and the four people in front of me all gave up because they were afraid of the danger in the nighttime hemisphere. So the staff looked at me with an indescribable look, a mixture of expectation, pleading, and many other emotions.

"Unlike most residents, I have always had a desire to travel around the planet. When I was five years old, the seed of this wish had been deeply planted in the soil of my heart, so I could not bear to see the seed that had grown for decades end its life like this. Besides, the idea of saving the inhabitants occurred to me. I thought that if I gave up when I was the last volunteer, then we could only live in this terrible fear forever. So I signed up without hesitation.

"The staff thought that this yellow," He said, pointing to the airship, "would expose me to possible danger, so I needed to disguise myself. They soon added a program which controlled emitting white light, which made the airship look like a star. To deceive possible danger and give me enough time to escape, several more airships were built and programmed so that they could be cleverly hidden in the stars by flashing at the same frequency."

The mind detector in William's brain showed him a picture. It was a field of golden wheat, fluttering and dancing in the breeze under the night sky. The frogs' clear and beautiful song floated everywhere. William looked up and noticed that some stars were twinkling at the same frequency in the sky.

He remembered. "This is what we saw at Griffin the frog's!" He cried excitedly, "I wondered what those stars were. The danger, however, made me forget the question. Now I have the answer."

"So," Ranran asked Handel, "you are going to find out what on earth caused these strange things to happen?"

"That's right."

"Wow, that's great! And have you found anything?" Rebecca asked. William looked at Handel expectantly, because he thought he might be able to tell him some extra information about You-Know-Who.

But he was disappointed. Handel shook his head in some disappointment and said,

"There are a few, but they're all places you've been. Sphere fighters told me this. Oh, by the way, I haven't told you how your sphere fighters found me.

"The airships were just flying over the 'C'-shaped building. Suddenly I heard the strange sound of engines. The stars were dim, so I couldn't tell from which direction the plane was approaching me. Before I had time to think, I was surrounded by a barrage of laser bullets. The airships immediately turned around and ran away at full speed. I looked back in alarm. The volley of bullets was still running after me like lightning, but there was still more volley coming from another direction. Those bullets lit up the night sky with brilliant light. From a distance, it looked like a colorful rainstorm. About a few minutes later, there was a loud noise behind me. I looked back and saw a huge flame burning, going down to the ground. Then I turned around to find several more white sphere shadows beside me. They told me about you guys and that they just shot down the bomber that tried to kill me. I learned that you were in a fierce fight with a spider in the cemetery, and decided to meet you over these waters. That's why you saw the jack-o'-lantern descending slowly."

The party saw the light. No wonder the sphere fighters poked their heads out and called them into the airship. "Did you lose airships, Mr Handel?" Natalie asked, concerned.

"I only lost one." Replied Handel, "But it is good that you're all right. You were in much more danger than I was."

Suddenly, they heard the sound of fireworks soaring into the sky and exploding. The party quickly ran to the window of the airship, searching for the fireworks.

"Look! There it is!" Natalie's keen eyes spotted a red firework.