‘Well . . .’ Lug wriggled about in his robes a bit. ‘You were telling someone about a trip you made to the sacred tree in the north – to Nammu – back when you were . . . um . . .’

‘Alive?’ said Elowen. She didn’t seem to be bothered about what had happened to her although, Liska thought, it must have been quite upsetting to say the least. ‘Yes, we travelled there once. Not long after Arborven was founded. We had heard that there was a tree of light there whose opposite had been frozen in a glacier. The city elders thought we might be able to use its heart to stop our own shadow tree before it had grown enough to start spreading its corruption.’

‘But you didn’t,’ said Liska. ‘Take the heart, I mean. Why not?’

Elowen shrugged. ‘When we arrived, we found some of the local people still living near the tree. Just a handful. There had once been hundreds of tribes there, they said, but nearly all had fled as the glacier got closer. Still, we didn’t think it would be fair to take their tree’s heart from them. It would have killed the poor thing. And besides, the Undrentree and its opposite were only small then. Saplings, really. Using the heart of an ancient tree might not even have worked.’

The Undrentree . . . a sapling? Liska couldn’t even imagine how long ago that must have been. Just how old was this undead girl she was talking to? ‘But later on, when the trees had grown . . . Didn’t someone think to go back for it?’

‘Perhaps,’ said Elowen. ‘Except by then my family had suffered the . . . accident. Nobody in Arborven really listened to us much after that. And over the years the story of Nammu became a bit of a legend. I don’t think anyone really believed it was true.’

‘They still don’t,’ said Liska. ‘When we found out that Nammu was real, we tried to tell the treekeepers but they all laughed. Now everybody thinks we’re useless children who believe in fairy tales. Except the city is really under attack from the rot, and nobody even wants to try to get Nammu’s heart. Apart from us, that is.’

‘Oh, yes,’ said Elowen. ‘The attack. I felt the commotion through the ground. When I came up to investigate, I saw the brave shapewalkers battling the invaders. It was quite terrifying. The rest of my family slept through the whole thing, of course.’ She paused and looked long and hard at them for a moment, her head cocked to one side. ‘Are you really thinking of going to find Nammu yourselves?’

‘Of course not,’ Lug began. ‘That would be ridiculous. Although Liska did mention it, but I’m sure she didn’t mean . . .’