They cleared the crest of the volcano and paused on the rim, looking down. Below them was a steep slope of blackened stone. A deep bowl shape and, at the bottom, filling the crater completely, a twisted thing from her worst nightmares.

The shadow tree was a writhing, jittering mess formed of patches of the deepest night. Like someone had scratched and scribbled at the surface of reality itself, tearing through to the dark emptiness beyond.

Whereas the Undrentree and Nammu had poured out magical energy, this thing sucked it all in. It drained everything around it – Liska could feel its hunger pulling at the marrow of her bones.

Could it even be called a tree? It had branches of a sort – jagged, bent things like shards of broken glass – and some kind of trunk, but the wood moved over itself, slithering like the scales of a coiling snake. Liska thought she saw glimpses of faces there. Things with wide-open mouths lined with shark’s teeth. Hints of spider eyes, glassy and empty of all feeling. Clawed hands pressing against the bark from within, trying to escape.

Above it hung a cloud of greasy smoke, pulsing in gusts and eddies, rising up from the volcano’s mouth and coughing outwards.

Spores, Liska realised. The thing was constantly spewing out millions of rotten particles that would land and spread poison. And it would never stop, she knew, until the whole world was covered in death.

Everyone was frozen in place, staring in dumb horror, fighting against the waves of sickness and revulsion that flowed over them.

The tree seemed to stare back, willing them to come closer, hungry to corrupt them, to kill them and then suck all the goodness out of their bones as they lay amongst its roots.

And then there was movement: a figure cloaked in a torn black robe, stumbling out from behind Bitterblight and looking up at them with eyes that bubbled with madness.

‘Noxis,’ Liska managed to say. She clutched Nammu’s heart tightly to her chest, feeling its flow of magic ease the nausea a touch.

‘Is that it?’ Noxis was shouting up at them, his voice teetering on the edge of hysterical laughter. ‘Is that all Arborven has to attack me with? One lonely treekeeper and some children?’

‘M-monster,’ Embla stammered. She took a step down into the crater, battling against the waves of evil power that pulsed out at them.

Elowen was struggling too, her hands shaking as she tried to form a spell. Her jaw clenched with effort, her eyes flashed blue . . . but nothing happened. ‘There’s nothing here,’ she said. ‘No roots or seeds to control. Arbomancy is useless.’

‘Your tree magic won’t work here.’ Noxis could see what she was trying to do and found it hilarious. ‘There is only the power of Bitterblight!’