It was now midnight. It was still snowing outside, as if it was the precious gift from the stars to this planet. The roads were long gone from the hustle and bustle of the day. Everything was quiet. The stores had long been sleeping in the night, receiving the holy bath from the snow.

The only sound in the room was the beeping, bobbing sound of flames and the breathing of the party.

All of a sudden, a strange scene happened -- the chip Sophia had picked up flashed a few lights, and then, from the body of the party floated out several shadows, being respectively their appearances. The shadow hung in midair, then drifted past Tabby cat's door, up the stairs, and toward the little hole. And they themselves were just sleeping.

They were sleepwalking.

The shadows stopped in front of the hole. William's lips twitched a few times, as if he were saying something. Then the shadows all nodded, quickly gathered together and went down into the ground.

The strange smell came again. Although the lights in front would automatically light up, yet it was a pale color. This time, they could hear the whisper. It was very far away, very faint, but very clear.

As they went deeper into the ground, strange marks began to appear on the steps. "What do all these mean?" Ranran asked.

"I don't know." William replied, shrugging his shoulders.

When the steps came to an end, a purple door appeared in front of the party. It had a pattern of lightning, with a special color on it -- a mixture of white and red. Then a soft, silvery ray of starlight flowed down and fell upon the mark. Instantly a murderous air rose. At that moment William felt for the laser gun -- William on the bed did so, yet he was still asleep.

But he did not fire, and removed his hand. They continued to gaze at the door.

Suddenly something hit them hard on the head and they fainted.

After an unknown amount of time, William opened his eyes and was surprised and disappointed to find that they were trapped behind the door. He felt a slight pain as he touched his head. He looked around and saw that everyone else was lying on the ground, too. Fortunately, they were all right. He was relieved.

"Everybody get up," He said, helping the others gingerly to their feet.

Then they looked around and saw how empty it was. Underfoot were all bright purple floor tiles. There was a huge blanket, neatly laid out, covering something. On a shelf behind William was a purple diary book with gilds on the cover and the name "Anna". On the next shelf was folded a sheet of paper. In front of them was a huge tea table with an empty cardboard box on it and a piece of... Button battery?

"What's in the box?" William asked.

"It's another button battery!" Natalie replied.

"Put them away. Is this a box?" Asked Photon, pointing to a green circular device.

"Yes, and the shape matches the two batteries perfectly." Ranran said and put the batteries on. The box opened, with eight lithium-ion batteries and a charging cable neatly packed inside. When she put away the batteries and the charging cable, she saw a folded note below. It said,

These batteries are a gift for you. Please keep them well. If you see a lightning mark later, please feel free to take out and use.

Photon found a small key in the tea table and put it away. "Maybe it can unlock something," He muttered.

Sophia found something, too. She picked up a pen in a corner. There was only one thing unusual about this pen -- it had a white lightning sign on the holder, very similar to the one on the door.

"Does that mean something?" She watched and thought.

"I see a white box here!" Natalie exclaimed excitedly as she lifted the blanket.

William reached for the piece of paper on the shelf. When he unfolded it, he was stunned. It had a picture on it that looked like a circuit diagram, with some lines and symbols:

"What does that mean?" He scratched his head in bewilderment. Over here Natalie had opened the box.

He saw some words at the bottom of the picture,

This is a schematic of the structure of the bomb in the white box. B is the initiator, and when an electric current passes through, it will explode. Wires A and B in the box will be exposed and have switches respectively. You need to cut a switch on a wire to keep the bomb from exploding. If you succeed, you will get a clue to the door. And if you fail, then... Ha ha ha!

"Be careful! That's a bomb!" Cried William, darting to the box with the paper tightly in his hand.

He knelt down and examined it carefully. It was exactly as it had said on the paper: there were two wires, each partly exposed, and the insulation was red and blue respectively. The red wire said "A" while the blue one said "B". The two wires also had a knob switch respectively, marked "1" and "0", and at this time both switches were placed at "1". In the upper left corner of the box was the monitor, and next to it was a green light.

The monitor suddenly lit up, and a few seconds later, the screen began to count down from 10 minutes. "Tick, tick, tick..." One after another, a clear prompt tune sounded.

"Aargh......... The bomb will explode! Come on, William!" Ranran said in a hurried voice.

"Tick, tick..." The prompt tone was still ringing regularly. Half a minute had gone by yet they hadn't done anything.

"We need to cut a wire." William stared fixedly at the chart, now and then at the diminishing monitor. 9 minutes, 8 minutes 50 seconds, 8 minutes 45 seconds... Beads of sweat encroached on his forehead, as if he were thinking anxiously.

There were only eight and a half minutes to go. Looking at the two wires and the switch, William took out the picture again, drew on it with his hand, and muttered, "This picture means that the current flows from the positive side of the power supply through A to B, and from A to the negative side through the indicator light. Since the current preferred the branch with low resistance, and the resistance of a section of wire is very small, so the current almost all passes through wire B, causing the initiator to be short connected. If I cut wire B, the short branch to the initiator will be broken and the current will have to pass through the initiator. Then the bomb will go off."

"Tick, tick..." Eight minutes to go.

William shook his head and continued, "So it's dangerous to cut the wire B. Then we'll have to cut wire A. Let's see, when you cut wire A, the way along which the current goes to both the positive and negative side will be broken, so it's safe to cut wire A." After thinking for a while, he finally decided, then clapped his hands and cried loudly, "Turn the switch on the red wire to '0'!"

Natalie closed her eyes and pinched with the front wheel very slowly. "Tick, tick..." The switch wasn't cut. Seven minutes and 45 seconds to go. The others closed their eyes, too. William and Ranran hugged each other tightly.

Natalie grew more nervous, but suddenly, from nowhere, a force made her flip the switch. The numbers on the monitor stopped changing. After a few seconds, a "Ding Dong" was heard, the number disappeared and the indicator went out.

The bomb was successfully defused by them.

"Yeah!" They jumped up with excitement. William squatted down again and found that this time a keyhole popped out of the box. Seeing this, Photon inserted the small key that he found in the tea table and gently twisted. The keyhole was unlocked, and inside was a delicate little gift box. Natalie took it, tore the ribbons and took off the lid. She saw a note and four blank boxes inside. The note read,

Friends, if you can deduce the code from these clues, please write it in the box. If you can't, this is where you're going to die!

Numbers Corresponding descriptions

Note: Numbers not specified are all incorrect

9178 One number with the correct value and position

2364 Two numbers with correct values, and one of them is in the correct position

8045 Two numbers with correct values, but both are in wrong positions

0267 All incorrect

8190 One number with the correct value and position

5678 One number with the correct value, but not the correct position

3724 Two numbers with correct values, and both are in correct positions

Password: ？？？？

"What is this? "Natalie cried, desperate and helpless.

"There are examples, and information about the examples comparing to the answer..." Photon whispered.

"The first thing we use is condition 4 -- 0267 all incorrect. So if you plug it in to condition 1, you can get that a right number could be 1, 8 or 9." Once again William stroked his head calmly and analyzed.

Sophia took out the pen she had found and wrote down what he had said.

"Hmm... By plugging it in to condition 2, we know that there are two numbers in the password that are 3 and 4, but one of them is not in the corresponding position. After we put it in to condition 3, we guess that the number 4 must be included, but not the third digit. Another correct number might be 5 or 8."

"So what does condition 5 mean? It's similar to condition 1." Natalie leaned in, too.

"Let's see... Oh! Did you notice that in both conditions, the position of the number 1 is the same, and the description is also exactly the same? So the number with the correct value and position must be 1, which comes in the second digit. So 8 and 9 are wrong. So according to that and the conclusion, number 5 is also correct, but not the fourth digit.

"We notice that condition six indicates that 5 is not the first digit either. And the second digit has to be one, so 5 has to be the third digit."

"So that only leaves numbers 3 and 4, right?" Sophia asked, holding her note.

"That's right. Now compare condition 2 with condition 7. And for the same reason, 4 is in the fourth digit. So we have 3 in the first digit. The password is 3154." William said the code, then clapped his hands and said, "Yes, it must be! Write!"

It was Photon's turn to volunteer. As he wrote, the words glowed purple, then both the door and the lightning symbol on the pen flickered. The door opened.

"Wonderful, William!" The others hugged him and cheered loudly.

"It's OK, we'd better hurry back." They went out of the door and were just going up the stairs when two things flew up in front of them. One was a mosquito robot with buckets of water and bags of fertilizer attached to it. The other was a box full of gold bars, which were exactly the shape Sophia had described!

"So it's you two!" Sofia hugged them happily and explained to the others, "These are my two right hand men who mysteriously disappeared a few weeks ago. I didn't expect that they were hiding here!"

They all laughed and floated up the long flight of stairs to the ground. The stars still shone, and the snowflakes danced with delight, decorating the planet with their white bodies.

The shadows floated once more into the quiet room and crept inside the party's bodies. All the items they found in the room fell silently to the floor and gradually fell asleep in the quiet night. And the mysterious little hole, after they had left, gradually closed.