Nothing Lug said was making any sense and he was getting more and more upset. Liska realised she was going to have to calm him down somehow. With a sigh, she unfolded her arms and tried to look less threatening, a skill she wasn’t naturally very good at. ‘Look, start from the beginning. Take a deep breath and tell me what the legend is.’

‘Yes.’ Lug stopped flapping with his robe and nodded. ‘The beginning. So. There’s a story about another pair of trees, just like our Undrentree and Bitterblight, except far, far to the north where the snow and glaciers are. Have you heard it?’

Liska shook her head. She had never been very interested in legends or any other part of the world that wasn’t the Shield Mountains.

‘Well, the ice there moves in giant sheets – slow but unstoppable – and eats up everything it comes across. Cities, villages, farms, all vanish beneath it as it shifts. And of course it destroys sacred trees too.’

‘So the trees up there are gone?’

‘Just the shadow tree,’ said Lug, his wide eyes beginning to gleam. ‘It got swallowed by the ice before it could attack. Which means the light tree is still there. Nammu it was called. Just think . . . a spare tree, with a heart inside it that could be used to destroy Bitterblight! We could kill it with Nammu’s heart and leave the Undrentree untouched!’

Liska took one of her locks between her fingers and rolled it back and forth, thinking. If it sounds too good to be true, that’s because it is. Her mother said that all the time. And she could see at least three major faults with Lug’s story already.

‘How do you know the glacier hasn’t swallowed this Nammu as well?’

Lug flinched. ‘Well . . . I suppose I don’t. Somebody would have to go up there and see. But I know it was still there some time ago. And glaciers move very slowly.’

‘And what about the city that owns Nammu? Don’t you think they’d be upset if we turned up, cut the heart out of their tree and ran off?’

Lug’s eyes gleamed again. He did a little jump from foot to foot. ‘There is no city! That’s the amazing thing! The people who lived there had to flee the glacier and move south. Nammu is just sitting there, waiting to be frozen . . . its heart doesn’t belong to anyone!’

Liska shook her head. ‘I’d like to believe you, Lug, I honestly would. But this does sound like some kind of fairy tale. If it was true, don’t you think the treekeepers would have been to this Nammu tree themselves?’

‘That’s just it!’ Lug looked as though he might pop at any moment. ‘Everybody thinks it’s only a story. Nobody takes it seriously! Except I know someone who’s seen it. I know it’s really true!’