‘Hmpf,’ said Liska. She had been quite looking forward to getting her revenge. ‘So, are you going to tell me your secret now? Your plan for getting rid of Bitterblight and saving the Undrentree?’

‘Not here!’ Lug hissed, eyes darting around the empty corridor. ‘The trees in Arborven have ears! I’ll tell you when we’re back where I live, where it’s safe.’

He led them out of the school, in between the jumble of roots and on to the Undren Square. Liska looked up to where the titanic branches of the tree blocked out the sky, hundreds of feet above, and imagined herself swooping and gliding between them. Part of her wanted to spread her griffyx wings and take off, but she had to admit she was intrigued by Lug’s secret. If he wanted to keep it so badly, surely it must be worth hearing?

She glanced across at the scrawny boy. The way his round head seemed to wobble on his skinny neck. His habit of twitching his hands up inside his robe sleeves. He didn’t seem like a person who would know deep, dark, hidden things. But then – as shapewalkers like her knew better than most – people weren’t always what they appeared to be.

The pair made their way across the open ground and into the first circle of trees that curved before them like a leafy wall. They were all oaks, as thick and gnarly as any Liska had ever seen. Some must have been hundreds of years old.

Most were built around with the houses of the arbomancers. Each of these had several floors and extra rooms jutting up all over the place in miniature turrets. They lined the branches and swallowed the broad trunks of the trees, and all were of the same style: dark oak planks, trimmed with silver-painted carvings.

Wide, arched windows with coloured glass panels let Liska peer into libraries, kitchens, greenhouses, studies, bedrooms, conservatories . . . every room you could possibly imagine. The furnishings were of the highest quality, the paths and gardens swept and trimmed. Not a blade of grass was out of place. It made Liska want to scratch the place up a bit, just to make it look real.

One or two buildings were shops selling food, flowers, gardening tools or tomes and scrolls filled with scribbled spells. They paused at a baker’s to buy a paper twist of almond and nutmeg cookies, which they munched as they walked. In between nibbles, Liska peered at the city folk, fascinated by how different they were to the military shapewalkers of her home fort.

Mages wandered in between the trunks, dressed in black robes, lined or embroidered with glittering silver. Men and women, old and young, they all held themselves with supreme confidence. Whenever one of them spotted Liska and Lug, they raised their eyebrows as if wondering what such lowly creatures were doing in the circle of the arbomancers.