Anna was jealous of the robots.

Their eight legs were separately articulated, designed perfectly for scuttling across uneven rock. And they were small enough to stroll down claustrophobic tunnels where Anna and the others had to take off their backpacks to squeeze through.

The machines would’ve lost her within minutes, except for the bungee cord. She used it like a leash, pulling back the broken robot every time it got too far ahead. When she gave it a tug the other robots would lose their grip, then come back and investigate. Sometimes they would detach the bungee cord, but Anna simply clipped it on again.

They weren’t very smart robots. But their behavior made perfect sense if this jungle really was artificial. They were programmed to ignore anything living, to interact only with other machines. In other words, they were maintenance robots, which was why they’d tried to steal Kira’s flashlight and the gravity device.

Whatever they were, following them had to lead to whoever had designed all this. Someone who could create this kind of technology could definitely help Molly.

“You guys okay back there?” Anna asked.

Yoshi answered with an exhausted grunt.

Anna couldn’t blame him. Crawling through these tunnels was tiring, especially after a day of jumping and that endless climb. Her muscles were rubbery, her jacket drenched in sweat. The rocks around them seemed to grow hotter as they went deeper into the mountain.

But none of that discomfort was enough to drown out the numbness in Anna’s heart.

The airplane had burned up so suddenly, like a giant firebomb, so fast that if anyone had been asleep inside, they wouldn’t have escaped—

Jet fuel burned at about a thousand degrees. Hot enough to reduce a human body to ashes and shards of bone.

Anna shook off the thought and kept crawling. The only way to help her friends was to find whoever had made these robots.

There was something ahead, a shift in the color of the rocks.

“Turn off the flashlights,” she whispered.

Yoshi repeated the command in Japanese, and a moment later Anna was in darkness. It took a moment for her eyes to adjust, then she saw it clearly—an orange glow just ahead.

Maybe it was bioluminescence, just a colony of glowworms. Of course, if the glowworms in this place were like everything else, there would be no “just” about it.

Kira said something, and Yoshi translated, “Do you hear that?”

Anna listened, and a soft fluttering sound filled the air. Like the wings of a flock of pigeons, or cards being shuffled in some large, echoey space.

The bungee cord went slack.

A she crawled ahead, the passage widened and the orange glow grew brighter. Anna saw more machines gathered around the broken robot. It was being dismantled, the pieces carried away.

Yep. Maintenance robots, scavenging for spare parts.

She reeled the bungee cord back in and shoved it in her pocket.

“I think we’re here,” she said. “Wherever here is.”

The tunnel opened up into a huge cavern, the size of the gymnasium back at Brooklyn Science and Tech. Inset into the stone walls were countless orange lights, all of them dancing on and off. It was hot, like a Laundromat in midsummer, but cool drafts spilled from another dozen passages leading away into the rock.

Across the floor scuttled dozens of the eight-legged machines. They carried pieces of metal and clusters of fiber, and navigated around Anna’s feet without hesitation or interest.

“Hello?” she called. Her voice echoed, but no answer came except the fluttering sound of the blinking lights.

“Omoshiroi ne,” Kira said, crossing to the center of the cavern.

Floating there was some kind of display, a hologram or a model. One end of it seemed to represent the jungle, familiar from the view they’d seen out of the mouth of the cave.

As Anna went closer, she saw that the rest of the model represented a long, ragged valley, a rift carved into the earth. The rift was bordered by high stone walls on either side, and tiny waterfalls poured from the rocks—the model was moving.

Near the center of the jungle was a glowing fire, the crashed airplane rendered in perfect resolution, not even an inch long. The two artificial moons hovered a foot above the trees, glowing red and green.

“Whoa,” she said.

Kira stood on the other side of the display, already drawing.

“It’s a machine,” Yoshi said.

Anna nodded. “Some kind of hologram, maybe.”

“No, I mean it’s all one big machine.” He pointed at the display. “The jungle is held in by these walls. The waterfalls and mists pour down to keep it wet. Every bit of it is artificial.”

“Sure.” Anna narrowed her eyes. “But if this is all a machine, what’s its purpose?”

“To maintain the jungle?”

“Um, jungles maintain themselves. It takes a lot of effort to kill them.”

Yoshi shrugged. “That depends on what’s behind this wall.”

Anna peered closer at the model. It only extended to the walls of rock and didn’t show what was on the other side. Farther down its length, the red and green of trees faded into other colors—beige, ochre, a few bands of glimmering silver. They weren’t as high resolution as the jungle, but each looked like it was some different kind of terrain.

Anna reached out and touched the display. It wasn’t a hologram at all—it was really there, but it felt as soft as cotton candy.

Some kind of aerogel? That moved?

The display also pulsed and shivered with data—swirls of color hovered over the crashed airplane, flashing angrily.

Kira said something, and Yoshi translated. “She says this place was built for dozens of people to work in.”

Anna nodded. The smooth expanse of rock overhead was at least twelve feet high, but the little robots only needed a few inches of clearance. She imagined people standing around the display, reading the mysterious graphics, drawing their plans for the jungle below.

But where were they now?

The cavern suddenly felt empty and haunted. Like the crashed airplane after the passengers had disappeared. Nothing left but mindless machines.

No one to help with Molly’s sickness.

“Is anybody here?” she yelled out.

No answer.

“Maybe it’s all automatic,” Yoshi said tiredly.

“Then who’s this display for?” Anna demanded. “The robots don’t need it. I’m not even sure they have eyes!”

One of the little machines was nuzzling her foot, and Anna felt a rush of anger at its mindless skittering, at all these signs of civilization that had promised help for Molly but now offered nothing.

The robot extended a whisker, reaching up for her backpack. Anna gave it a swift kick, and it clattered away across the stone.

“Um,” Yoshi said. “Maybe you shouldn’t do that.”

Anna didn’t answer him—the other end of the model had caught her eye. There, opposite the jungle, was some kind of structure. It was as big as a dinner plate, ten times larger than the tiny crashed airplane. Kira stood at that end already, drawing it.

Anna went to take a closer look.

It was covered with spires that stuck out in all directions—a madhouse version of a castle, or maybe a futuristic city. The structure’s core gave off a soft red glow, pulsing like a heartbeat.

Whatever it was, there had to be someone there.

People with answers. People who could help Molly.

Anna pointed at the structure. “This looks like the headquarters for whoever built all this. We have to get there!”

Yoshi looked down the length of the model, then back at the jungle.

“That seems pretty far.”

“But we have to try,” Anna said, but he was right. The hologram stretched endlessly down the cavern. A panic started to build in her, the feeling that no matter what they did, they would be too late. “Maybe we should look around. Find something that might help Molly.”

“Okay,” Yoshi said. “But what are we looking for?”

“Anything!” Anna glared at the little robots underfoot. Most of them carried spare parts, pieces of metal and wire and plastic. Something had to be worth plundering.

She crushed one of the passing robots underfoot.

“Anna,” Yoshi pleaded. “Be careful.”

“They’re just repair bots,” she said. “They don’t even see us.”

He opened his mouth to argue, but suddenly his expression changed. He was staring over her shoulder, frozen.

Anna followed his gaze—at the opening of one of the passages was a new kind of machine, much larger than the little robots. It hunkered in a menacing crouch, its four legs and two arms folded around it, each ending in large, sharp-looking pincers.

“Uh-oh,” Kira said.

The machine rose up, its arms waving, their pincers snapping like metal jaws, and cold fear swept through Anna.

Yoshi took a step backward. “What on earth is that?”

Anna swallowed.

“I think it’s animal control,” she said. “And we’re the animals.”