"Here? This cabin?" Natalie asked in surprise, pointing with her right front wheel.

Plane 1 and 2 nodded. They didn't say anything, just going at full speed. "Hey, wait for us!" The cries of the others were drowned in the sound of the wind whistling in their ears.

Photon made an emergency stop, and Natalie rear-ended Plane 2. "Ah... It hurts! What a thick iron plate you have!" She groaned in pain.

"Come on, won't you? I've got a carbon fiber composite tail." Said Plane 2 with disdain.

"What a coincidence, just like me." Photon said.

William knocked softly on the door, then retreated a few steps. After a few seconds, the door opened automatically and a dark figure crept to the door. The party examined him. He was dark and his huge body was split in two: the front end was a flat cuboid with an 8,640p HD camera; the back end was a sphere containing a sophisticated microcomputer. Eight claws, bent, protruded from his front. All joints were equipped with minitype digital steering gears, which were controlled by the computer to execute drive commands.

"Hello, friends." He greeted the people other than the two planes.

"Hello," William replied with a friendly smile, "are you the spider that Uncle Sam sent to spy on Capsule Laboratory?"

"Yes, it is me." The spider robot raised his right front leg, nodded and replied, "Come in, everybody."

The last incoming Plane 2 closed the door. They stepped on the intricate wood floor and looked inside. The chimney passed between the huge beams that hung above the sloping roof. Beside the opposite wall was a wide and comfortable sofa, matching the tea table with a black glass plate. The living room was connected to the balcony, where a small, three-drawer cabinet lay quietly, storing one necessity for the secret tunnel.

The spider robot invited them to sit down and said, "You're going to save Thomson's gene-edited cat, right?"

"Yes. Did Uncle Sam tell you?"

"Certainly." The spider replied to Photon who was puzzled, "In fact, it was Thomson who told Uncle Sam, then I and Black Ghost knew that the cat had been caught."

The party nodded. Then the spider continued, "Black Ghost told me you came from the wetland, didn't you?"

"Do you mean the wetland that holds the remains of animals that have been stripped of their special genes?" Photon asked him, rousing himself. The spider nodded.

William, imitating his movements, nodded too. "You're a fast learner." Said the spider robot, and everyone burst out laughing.

"Well, I promise I can take you with me to Capsule Laboratory and save those poor animals, but first I want to tell you something else." Laughed the spider robot mysteriously.

"Something else?" The others chorused.

"Yes, something else. Once I was walking with Black Ghost in a grassland when I came upon a delicate little box. Out of curiosity, I put it away and put it here. Let me show you."

So the spider jumped off the sofa, ran to the cabinet on the balcony, opened the bottom drawer, and took out a small bronze box. He put it on the tea table, then the party all became onlookers. The box was not very large, but it was locked by a mechanical structure. To pull it directly would require the thrust of at least three jet engines, which was about 40 to 50 tons. Now Photon had only 3,300 horsepower and Natalie had 1,000; Plane 1 and 2 had in total eight engines, each with only about 1,800 horsepower. Clearly this was not enough. So if he wanted to see what was inside, one had to be clever. And the only help was the upper six rotating shaft type combination lock.

"It's all flowers?" Ranran carefully observed the combination lock, saying doubtfully.

Suddenly, William, who was sitting opposite her, noticed an area on the box where the texture didn't match. "Wait, Ranran," He called her.

With a puzzled look on her face, Ranran handed him the box. He took it and quickly found the strange place. Touching it, he felt as if it had been papered over, while it did not belong to the box.

So William pulled his hand hard at the edge of the area. It did tip up a corner, and the exposed texture fitted in nicely with the rest.

"See? I told you it was weird in here." He took the layer of paper off and found these words in small print,

Please take a trip to the wetland and pay special attention to the floral patterns. The truth, which lies in a series of seemingly ordinary coincidences, belongs only to the observant.

"A trip to the wetland? Was that the hint we just got?" Natalie speculated.

"Your guess is very reasonable," Said Plane 1, "because we haven't used them yet."

"What do the numbers mean?" Staring blankly at the combination lock with the floral patterns, Natalie twirled the roses in the first row. Suddenly she caught sight of a "5" on one grid and a "0" on another.

"They're all the same... Do you want to find a rose numbered seven?" As she pondered, she felt Photon touching her.

"What have you discovered?" She asked.

"Look at this." Photon pointed to "X: ↑ ↓; 0,1,2,... , 9: f (x) " on the left side of the password lock, and "f'(x) > 0" on the right.

"Why are there derivatives?" William scratched his head and muttered to himself in confusion.

"Wait, will this 'X: ↑ ↓' refer to twirling the patterns up and down?" He suddenly understood, "So '0,1,2... 9: f (x) ', so that means the number is f (x), right? As for 'f'(x) > 0', it should refer to the increase of the number when twirling up as well as the decrease when twirling down, huh?"

"There is something to it!" Cried Plane 2, "The number seven rose should be..."

"Twice up!" Natalie tried it and heard the unlock click.

"Wow! Really!" She jumped up with excitement. In keeping with this rule, they managed to come up with the following passwords. Just as William's hand placed the tulip pattern in place of number 2, the box unlocked itself and opened.

Inside lay a small golden key and a piece of paper folded outward in the shape of a small house.

"Wow! A key! Can it unlock something!" Ranran held it in surprise with both hands, ran to the spider and shouted.

The spider took it and looked at its shape. "It is the key to the secret tunnel, as well as the code that cannot be cracked." He laughed.

"Yeah!" The others shouted excitedly again.

"Wait, there's one thing you're missing." The spider robot took the paper out of the box, unfolded it and handed it to William. He opened it and read,

William,

If you can see this paper, it means that you have successfully cracked the code of the box by the hint of the wetland, and obtained the key to the secret tunnel. Congratulations! Black Ghost planes and the spider robot are familiar with the way to the lab. They are also qualified guides, so all you and your friends need to do is to follow them! Also, maybe there's another thing you'll find as you get closer to the lab, which I didn't tell Black Ghost but told the spider, because I wanted to give you a surprise.

Good luck saving the gene-edited animals!

Sam, in the testing room in Garage 95

"Uncle Sam wrote this?" Asked William, looking surprised.

"We didn't know he had the key here. After the first spy, he only told us that he would keep the key perfectly safe, which was certainly not what we expected." Said the spider, shrugging his shoulders with his ingenious steering gears.

"My goodness, I didn't think he would hide the clues in such a way!" Exclaimed Photon, "In that wetland, and especially that terrible mirror! If we had given a little effort, Master would have fallen into the water!"

"That's not the worst of it. The worst part is when you fall there's a stench of decay from some poorly preserved remains." The spider said.

"But why didn't we smell it above the water?" Natalie asked again.

"That must be because you came in the dark. Starlight is not enough to illuminate what Uncle Sam put on the surface of the water -- activated carbon. They pick up most of the odor that comes up above the water, but there's less activated carbon underwater, so the odor is stronger."

Natalie nodded.

"Besides, he was worried that his racing car would be found by the sports car in the lab." Said Plane 1, clapping William on the shoulder.

"Oh, you don't have to. You just need to make sure that your car has enough fuel to burn for half an hour at a sustained speed of more than 300 km/h." The spider said.

"No problem. Natalie's tank has been optimized by Uncle Sam to be 180 liters, so it should be no problem to do that. But why do you ask?" William said.

"Because I've seen the statistics on the sports car. Although it is known for its power and speed, it has two serious drawbacks. One is its extremely poor cornering ability -- it may only be able to get through hairpins at 40km/h. The second is its poor endurance -- the fuel is only enough for about 10 minutes at rated power. And that's not all. When it's accelerating between 150 and 300 km/h, it costs more fuel than running at top speed. I think on both counts, your Natalie wins, so even if she does get caught in the process of saving the animals, you shouldn't panic. We've got a lot of sharp turns in the secret tunnel, so I'm sure you can get away with it."

"The robot has a point, Master. Before I was a real racing car, weighing only 1.3 tons, with nothing to spare except a few things to make you more comfortable. But the diesel engine your father installed for me tends to be high-revving, so there's not enough torque, which means it takes me four seconds to accelerate to 100 km/h. Uncle Sam converted me to a four-wheel-drive layout, complete with air conditioning and other comfort features! Although this makes me weigh 1.5 tons now, the new powertrain he gave me has a combined torque of 1,300 Nm! The new layout also keeps me from oversteering; plus, with air conditioning, you don't have to sweat hard driving me. Though that still cannot be equated with the performance of that sports car, yet for me it's a leap forward. So trust me!"

With that, Natalie lifted both front wheels and swung them in the air.

William asked the spider robot, "So you're saying that I can use Natalie's amazing cornering ability and the torque of the hybrid system to establish an absolute advantage in the corners?"

"Bingo." Said the spider, who did a back flip.