Mucum breathed a sigh of relief. “That’s the one. Your little sis is ’ere wiv you, right now, laughin’ ’er ‘ead off!” He followed Ark down as the light above him dwindled into a spot, then a pinprick, then … he shivered. His eyes were now useless. If he fell, it might be all the way to the center of the earth. “We’re gettin’ there, mate! Yer doin’ all right.” The trick was to fill this emptiness with words; otherwise the blackness would soak into his eyes, stuff up his lungs, and … “How yer doin’?”

Ark gave an invisible smile. “Fine. Legs ache a bit.” Blood oozed from cuts on his fingers as the rusty metal bit into his skin. Hand, foot. Hand, foot. Ark’s thoughts drifted as they descended farther from all they knew. What were they? Tiny insects drifting down a single water shaft, one among a million trees.

“How deep d’yer reckon this goes?” Goose bumps on Mucum’s skin told him it was growing colder. His voice sounded different, as if the echo had been swallowed.

The voice brought Ark back. “A mile for the height of the tree, but the roots could go down much farther.” His eyelids felt odd. Something forced them open. “Look!”

The word finally meant something. Mucum stared. His eyes, grown used to the endless beetle-blackness, were suddenly shocked. Light seeped up from beneath them. And the rungs had taken on a different quality. They were no longer rusty, but smooth and cool to the touch. “Told yer!” he said. The shaft had widened significantly. “Must be near the bottom!”

Visibility increased, though they couldn’t see where the light came from. The walls were lined with a lush carpet of plant life that clicked and skittered with bleached white beetles.

“Look!” said Ark again.

Dotted amongst the ferns were millions of pairs of shiny black oval shells, which gave off a tangy smell that made Mucum’s belly lurch with hunger.

Ark’s silent prayer of thanks was interrupted by an ominous rumbling sound, followed by a rush of air that filled his lungs with the scent of the sky. As if in response, every single shell snapped open, revealing a yellowish, glowing pod plopped at the center. It was like watching a flock of lit-up butterflies unfolding their wings. “Let there be light!” he whispered. With one hand hooked on a rung and his legs anchored, Ark reached with his free hand through the fronds of a plant to touch one of the pods. It was soft and alive, quivering under his fingertips. The moment he removed his hand, the shell clicked shut.

“While you’re playin’ with your new pet, have you worked out what’s goin’ on yet?” The look on Mucum’s face was pure terror.

“What?” said Ark, entranced.

The shaft now echoed with the sound of the shells sliding against each other.