Ark heard a soft scraping sound directly ahead and coming in their direction. He motioned to Mucum. They both did as Joe suggested, taking one step backward, then another, hoping not to trip up, trying to make out the source of the noise.

“Could be a little one. If yow get the chance, aim for the mouth.” Joe had his harpoon raised.

“This ain’t like some kinda game with yer Rootshooter buddies?” asked Mucum hopefully.

Joe threw back a sharp stare, all bumbling friendliness vanished in an instant.

“No. Right. Jes’ askin’.”

They retreated toward the nearest side passage as the slithering grew louder and the walls of the root began to shake.

Something big was coming their way. Ark’s mind went into overtime. Maybe Joe was wrong. It sounded more like a roof collapse or even a tree fall. It happened occasionally despite all emergency engineering. Trees were alive. They grew old. They died. And when the massive trunk slammed down into the forest, Diana help any who had not made it out in time. Whole neighborhoods could vanish in seconds, leaving a gap in the map, a part of Arborium gone forever. If this tree fell, it would lift up the roots and anyone stuck inside them. They’d be tumbled about like fish in a cruck pool.

Joe ducked down into the side passage, motioning the boys to crouch. The sound filled the main tunnel now, booming into their ears, crunching, slithering, sliding.

“It’s not a little one,” said Joe, sighing. “It’s trouble, all roight!” He took one of the cloudy glass bottles, shook it once, and threw it out into the main passage. There was a tinkling smash. Dim phosphor and shadows gave way to a bright swarm of intense light as a thousand glowflies relished their short-lived freedom.

Ark bit his tongue in shock, feeling the blood well into his mouth. Both he and Mucum looked up, and up again, trying to take in the scale of what they saw as their feet stuck like lichen to the spot.

A segmented monster with a bruised-purple pulsating skin squeezed and filled every inch of the tunnel, writhing and uncoiling toward them at high speed. On the end of what had to be its head was a mouth filled with gnashing teeth that wouldn’t look out of place in a sawmill. It had as much relation to a compost-munching worm as a mountain did to a pebble.

The monster briefly stopped, rearing over the three tiny figures, sensing vibrations. Anything that moved down here in its territory was alive. If the monster had lips, it would have licked them in anticipation. True to its name, the mealworm was hungry.

“I hope yow know some good prayers, boys!” whispered Joe through chattering teeth. “‘Cos otherwise, we’re trowly out of luck! “

20• A MEETING OF THE MINDS