Before them, a few hundred metres away, rose the sheer granite face of the western Shield Mountains. Up there, Liska knew, hidden in the clouds, was the ruined fortress known as The Breach. Guarded by winged pantherine and cockatrice shapewalkers – some of the fiercest fighters of her kind – it was the most important of all Arborven’s defences. Because, on the other side of the mountains, lay the Rotlands. Home of Bitterblight itself and teeming with the poisonous monstrosities the shadow tree had created.

The land between the mountains’ feet and the last circle of the forest-city was peppered with the odd leafless, stunted tree and hummocks of straggly grass. Wisps of mist crawled over the ground, and beneath it could be seen stagnant pools of dirty water and churned-up patches of wet mud.

‘Well,’ said Lug with a sweep of his arms. ‘We’re here. This is the Scrubbings. Home sweet home.’

‘You live in a swamp?’ Liska had been expecting a humble tree house. Maybe a little copse. This place looked like a scene from a horror story about demonic frogs.

‘It’s nice and moist,’ said Lug, flinching at her reaction. ‘Good for the worms.’

‘It’s . . . um . . . lovely,’ Liska lied, trying not to wrinkle her nose at the damp, putrid stink.

That seemed to perk Lug up a bit. ‘We live in a burrow by that stump over there,’ he said. ‘Would you like to come in for a cup of tea?’

The thought of being trapped underground anywhere, let alone in a foetid marsh hole, walls seeping with mildewy water, filled Liska with horror. She was used to open skies, fresh air and freedom. Even walking between the Arborven trees had made her feel a bit claustrophobic.

‘That’s very kind,’ she said, ‘but I should be flying back home. The sun is almost setting. Perhaps you could just tell me your secret now and then I can be off.’

‘Oh,’ said Lug, blushing again. ‘Yes, of course. The secret.’

Liska sat on a nearby hummock of dry grass and folded her arms, waiting.

‘Well, it’s actually more of a legend, you see . . .’ Lug began. ‘A story, or a myth . . . about another set of twin trees, far in the north . . .’

A frown began to wrinkle Liska’s face. Had she really walked across the whole of Arborven to hear an old fable?

‘You said it was a secret. You said you had a way to kill Bitterblight. I thought you meant something real, not just a bedtime story.’

Lug twisted the sleeves of his robe in his hands, beads of sweat on his head, trying to find words to explain himself. ‘The legend isn’t the secret. It’s how I found out about it. And that I don’t think it is a legend. It might actually be true. But I can’t tell anyone how I know without getting into serious trouble . . .’