“Rain doesn’t fly,” said Elata.

“Sprays,” Seldom said. “That’s what I meant.”

Nissim said nothing, studying the boy that had unexpectedly wandered into his life.

Questions begged to be asked. Diamond wanted to know everything about rain, but he was also thinking about flying, and that brought the blimp to mind. “How do we stay in the air?” he asked Elata.

“Gas holds us up,” she said.

“Hydrogen gas,” Seldom added.

That first word meant nothing.

Sensing confusion, Nissim used a teacher’s voice. “Air is made up of different species of gas. Some are common, others rare. And the lightest gas is hydrogen. Certain plants make quite a bit of hydrogen, and we harvest what we need. Have you ever seen wood float on water?”

Diamond nodded.

“That’s what this aircraft is doing now. Floating.”

“But we’re falling,” he pointed out.

“That’s because the blimp always starts its run heavy. It begins up high and works its way down the tree. The air gets thicker as we drop. Do you feel your ears aching? Well, they might. Or might not, I don’t know about you. But the blimp falls, picking up more passengers and cargo, increasing its weight which helps it fall faster, and then it drops a little ballast, lightening the load just enough, after which it runs above the canopy to the turnaround point.”

“Ballast,” Diamond repeated.

“Sawdust and water,” said Seldom.

“Usually,” said Nissim. Other people were watching the conversation. His face needed to be closer to Diamond, his voice lowered. “At the end of the run, the pilot drops most of the ballast, and our blimp jumps back to the top of the world.”

Diamond stared out the window. The school and black blimp were far above; walkways and homes and elaborate buildings covered Marduk’s endless trunk.

“What’s at the top of the world?” Diamond asked.

“Not the sun,” Seldom said.

Nissim placed one hand on Seldom’s head, shaking him gently. Then in a whisper, he explained, “Not many go there, and nobody would want to live there. It’s always dark, always night. But that’s where Marduk and these other trees put up their roots. Against the world’s ceiling, everything hangs.”

The boy blinked and sighed. Hard thought brought another question, and he asked, “What is the world’s shape?”

Seldom smiled smartly. “Guess.”

Nissim frowned but didn’t reprimand.

“You don’t have to,” Elata said.

But then Diamond put up his hands, fingers and cupped palms drawing a sphere. In his mind, the sphere was smooth and perfectly proportioned. And of course it was enormous. And when nobody corrected him, he described what was in his mind, stressing the enormity of this realm about which he knew almost nothing.

Then he felt finished, and nobody spoke.

Diamond readied himself for corrections and laughter. But Seldom spoke first, nothing but amazed. “That’s it,” he said. “That’s what it is. The Creation is a perfect, perfect ball, and that’s all there is.”

The blimp and its floating gas kept falling. Diamond watched the world, and Nissim and Seldom and Elata took turns describing the world. It was as if the boy had two sets of eyes, one pair staring out from his skull while an even bigger pair was turned inwards, watching an imaginary ball filling with forest and people and the blazing, still unseen sun. The eternal sun lay at the bottom of the world. Hundreds of species of trees hung from the highest, flattest portions of the ceiling. The District of Districts was fixed to the top of the sphere, while Marduk was far out where the forests thinned and the wilderness began.

“Bloodwoods are much bigger than blackwoods,” Seldom said. “Marduk is a twig next to them.”

Diamond tried to imagine those impossible giants.

“The District of Districts is in charge,” Elata said.

“What does ‘in charge’ mean?” he asked.

“They’re the bosses,” she said.

“Like parents?”

Something was funny. When the laughter stopped, the Master explained, “There are nine districts, but nearly half of the population lives in the District of Districts. In all things human, they have the largest say. They take money from us and steer the laws, and while every District has its own army, they control the biggest army that keeps us safe.”

“My father was a soldier,” he said.

“Many serve,” Nissim said.

“What do they protect us from?”

“The papio,” Seldom said.

Elata shook her head. “We don’t fight the papio anymore.”

“Because we have armies,” the boy said.

She touched Diamond on the knee. “Mostly soldiers fight monsters. And other tree-walking people too.”

“What people?”

“Bandits in the wilderness,” she said.

“There’s other bad people too,” Seldom insisted.

Nissim looked around the cabin, his mouth shut.

The blimp was changing its pitch and velocity, propellers rumbling with purpose. Diamond pressed his face against the window glass, spying another landing jutting far out from Marduk.

“What’s the wilderness?” he asked.

“Dangerous,” Seldom said.

Elata said, “Beautiful.”

Nissim agreed with both answers. “Different trees grow outside the districts,” he said. “And there are different animals, creatures you would never see here. And once you move even farther out, out where the spherical world becomes vertical, another realm takes over.” He pulled a slick white coin from his pocket, handing it to Diamond. “The reefs are coral. This is cut from a kind of coral. It’s a hard, half-living material. What’s alive is part plant, part animal. It feeds on sunlight and gnats and feces, and the reefs are older than any tree, and that’s where the papio live.”

“Papio,” Diamond repeated.

One of the passengers was staring. She hadn’t noticed the odd boy until now, and when Diamond glanced at her, she grew self-conscious, looking out her own window with sudden intensity.

The blimp was docking. Diamond saw men standing together, waiting to board, and the burly red capables pulled hard at the ropes, fighting a breeze to bring the gangway into position.

“The papio live on the reefs,” Seldom explained.

“They look like people,” Elata said.

“No they don’t,” said Seldom.

Nissim put his face close. “The papio are complicated. Let’s leave it there for now.”

Diamond remained silent, wondering how anybody could understand the endlessly complicated world.

Horns sounded, and again the blimp moved. Three men entered the cabin and stopped in the aisle, talking to each other with their eyes. Diamond watched them, trying not to stare. One man nodded and another moved to the front and sat. The nodding man and his companion said nothing, filling an empty bench in back.

Diamond looked out the window while he studied the new world inside his head. “How far down do they reach?” he asked.

“Do what reach?” Elata asked.

“The trees.”

“Less than halfway,” Seldom said.

With stubby fingers, Diamond made the sphere again. Trees dangled down from the top and something called a reef grew on the edges. Seldom put one finger into his round cage, swirling where the trees ended.

“The canopy is my favorite part of the world,” Elata said. “That’s where trees make branches that grow sideways and wrap together.”

“Most of our food comes from the canopy,” Seldom said.

Nissim wasn’t talking, and he didn’t seem to be listening anymore.

“Days are brighter in the canopy,” Elata explained. “That’s where most of the sunlight gets eaten by the trees and epiphytes.”

“What are epiphytes?”

“Plants that hang from bigger plants,” Seldom said.

The world was steadily rising around them. Maybe it was Elata’s words, but the air did seem brighter than ever, and out from the last shreds of mist came a rich green floor that looked solid, impenetrable.

“There’s thousands of species of plants,” Seldom said.