After getting out of the slide, the party ran wildly. A dozen seconds later, they lost sight of the house of ghost. They could remember neither how many hills they had climbed, nor how many corners they had turned. The only thing that took up all their memory was that they ran for three minutes under the command "run".

Then, when they finally stopped to rest in an open flat area, the computer told them,

Sorry, but because of the size of the final checkpoint, you'll have to split up. Only you and Ranran can enter that place. Everyone else start the spaceship and get ready to back up.

"Oh, all right." Ranran could tell that Rebecca was disappointed. "Take care, you two!" Natalie said, "I'm sure you'll be fine!" Her engine gave a loud roar.

"Well, I don't know where the spaceship is..." Aria hesitated.

"It doesn't matter. My master gave me robots. They'll lead us to it." Photon replied with great interest.

William and Ranran took the white diamond they found at the kingdom of playing cards, and they watched the others disappear into the darkness. "Why does the computer say they need to back up us?" Ranran asked as she advanced toward the checkpoint.

"We won't know until we get there. But I hope it won't be so bad." William replied with assumed composure. In fact, he could very clearly feel his heart beating.

A few minutes later, a huge pyramid appeared in front of them two. William looked up and saw a faint light from the top of the pyramid. "What's that?" He asked himself, "And the pyramids are earthly objects. Why is there one here?"

With these questions, they followed the path at their feet to the entrance to the pyramid. Suddenly, a cold wind blew rapidly from the dark pyramid. It cut their faces like a sharp blade.

The compass suggested they become invisible again. Having just come out of the house, they did not want to feel that terrible feeling again, but they had to put on their clothes to be safe.

The faint light behind them soon disappeared, replaced by the endless darkness inside the pyramid. It was not as murderous as the house of ghost, but William and Ranran were still afraid. Illuminated by the light of the compass, they took each step with great care. They dared not exert force, as if they were walking on sharp knives. Their hearts hung in their throats lest some sudden danger should appear.

At their feet William saw that the road was made up of squares of golden stone, with plenty of strange symbols on them. "What do those mean?" Ranran asked. William replied, "We haven't found anything like a codebook, so we can't decode it just yet. Or maybe they don't mean anything at all, being merely symbols?"

He deliberately lit both sides with the compass. Nothing, because beside them there were only tall, hard walls of gold. Their tense hearts relaxed a little.

They saw that after a few dozen meters the road ended and it stopped at a closed door. So they stopped at the door, too. William noticed the words near the door:

Only after you enter the password and get through this door can you go upstairs. Next, look at the following hints and figure out the password.

☆ + ★ + ○ = -2

● × ☆ × ■ + ○ × □ = 0

☆2,135 = ☆ = - ★

☆ × 4 = ○ × 2 = □ = - ■

☆1/2 = i(imaginary unit)

Passwords: (☆ + ★ - ○ - ● + □ + ■)2,135

"Oh, dear." Ranran said, a little worried, "What does this mean?"

"Don't worry, I'll know the password in no time." William stared at the words, his mind racing, "The last condition says the white star is -1. If you plug it in to the third condition, then the black star is 1. And then we know that the white circle is -2, the white square is -4, and the black square is 4. So the black circle is 2. In that case, the password is... 0."

He walked to the door and pressed "0". The door slid slowly sideways. Then the checkpoint and the spiral golden staircase came into view.

They approached the checkpoint. The computer said the energy core had been fully charged and all they had to do was to go to the top of the pyramid and take it away.

"Oh!" Ranran suddenly realized, "It was the light of the energy core!"

"Yes, no wonder we saw that light just now." William said.

They went up the stairs. The strange thing was that the steps were also covered with those magic symbols, and the same symbols were exactly the same shape. It appeared that the symbols were not written by hand, but made by machines. This possibility had occurred to them, which was certainly, but there was no proof of it, so they went on.

William and Ranran went up the stairs to the second floor. Here, the corridor became narrower, and the doors became more numerous. The cold wind blew again, and at once they turned their backs on it.

William could faintly hear broken murmurs in the wind. Then he felt a slight pressure on his neck. He was having difficulty breathing and the blood in his body was slowing down. "There's the hand again," He thought.

But the feeling soon vanished before Ranran had time to notice something unusual. In a twinkling of an eye, darkness and silence descended upon them again.

"Open this door first." William opened a door with a picture of a nucleus. Four feet tramped in without a single sound. The light of the compass showed them that the room was not very large. Beneath the golden cone-shaped roof sat the only object -- a thin, glowing tube. As Ranran approached it, she saw a sign nearby that read, "Magnetic Tube: Used for Anti-matter Storage". She looked up and saw a mass of objects moving in circles in the tube.

William took out his compass and approached the tube. Using this method, he got the direction of the magnetic field. Then he used the left hand rule to verify. He was surprised to find that the objects in the tube rotated in the opposite direction to where his thumb was pointing. That is to say, the electrical properties of those materials were opposite to those of ordinary ones.

"Oh! It really is antimatter!" He said excitedly, "I've never seen what it looks like. They have to be restrained with a magnetic field, or they will explode once they are exposed to the environment!"

They went out and entered another room. This room was smaller so much that William had to bend over to get in and couldn't turn around. But what they saw was this,

It is a double-edged sword that can both make faster-than-light travels come true and cause serious damages.

Below "It" was an arrow pointing to a schematic of the structure of an anti-hydrogen atom.

"What?" Ranran said doubtfully. Soon they would understand the meaning of the words, which she did not know.

There was a screen in the room opposite. Almost as soon as they entered, the screen started playing a video. A hydrogen atom appeared on the screen, and an anti-hydrogen atom did too. They, at first, were far apart, in opposite corners of the screen. Gradually they came closer to each other until they finally collided. For an instant, the screen glowed bright light, and William and Ranran closed their eyes.

Then the screen went dark. There were more nuclei and anti-nuclei that came together, collided, and released huge amounts of energy. This energy turned into electricity, driving a white spaceship at top speed; it turned into a cannon shell, leaving a huge wound on a red seagull's body.

"Oh, red seagull!" Ranran seemed to remember something.

William nodded and said, "Yes, I know what you're thinking. We didn't know what kind of weapon had killed the red seagulls. Now we have the answer."

"Now I know what that means."

"It is so terrible that You-Know-Who has been killing creatures with antimatter for so long." William's body trembled slightly.

But they did not open the last door, for it was emblazoned in red,

Danger!

They heard the faintest "Zzz, Zzz..." from behind the door. The sound, faint as it was, sounded like thunder to the fearful them two. "Get away from this door quickly!" William hurriedly wrote on Ranran's body with his hand.

They walked as fast as they could to the stairs and continued up to the third floor. The purr died away, and both tense hearts were relieved.

William and Ranran turned forward. Their faces beamed with satisfaction at the sight of a familiar rectangle black object. It lay quietly on a golden platform.

"Energy core!" Cried William excitedly. He ran quickly to it, picked it up carefully in both hands, and looked at the magic weapon that had helped them make it through the black hole. It looked as if they had never met.

It was still the black shell, the blue glow of fluorescent band, an atom pattern, and the unfamiliar words embedded on one side. When he just came, he would never have expected to find it here.

The energy core glowed blue, as if expressing its joy at being reunited with its master. Ranran looked at it with a smile. William said, "I've found you, my precious. Let's go home."

The energy core flashed three times. They put it in the backpack and trotted along until they came to a platform and once more saw the quiet night sky. The earth was wandering in her sweet dreams, lying under the dim stars.

"We have already gone out of the pyramid?" Ranran couldn't believe her eyes.

"I think so! We can deactivate invisibility now." William said. Almost immediately, he received a message from Photon,

Master,

You'll be out of the pyramid soon. There is a golden road ahead, at whose end we will wait for you! Since the road ends at a cliff and has a certain slope, you and Ms Ranran can use the sprint monocycle to speed forward. The door of the ship will open and you can directly jump into the ship! We can know what is going on to you, so don't stop when you get to the cliff, just sprint!

"That's fantastic! When I go home, I'm going to treat my robots! Without their help, Photon would not know what were going to happen to me in time." Said William smugly, unaware that his foot slipped and he sat down on the ground with a deafening noise.

They were as still as stones. Then they heard the door on the second floor open, and the purr came closer and closer to them.

William whipped out a pair of sprint monocycle's tires for Ranran to put on. Then he said to her in horror,

"Run!"