Elowen, now calling on her magic as easily as breathing, stepped forward and laid her hands on the grey, frost-flecked bark of the tree. She began to sing in her arbomancer’s language. The effect was instant. About halfway up the trunk a crack appeared. A split that yawned open, revealing the sap and wood beneath.

Layers and layers of tree flesh peeled backwards, like a flower unfurling. Deeper and deeper into the tree they saw, until a glowing seed about the size of a watermelon was revealed. Blue light poured out of it in rays, making them all squint. Liska’s fur crackled with energy. It sizzled in her snout, it tickled her feathers. The power trapped in that small shell must be immense.

‘Our thanks to you, Nammu,’ Embla said, reaching in and taking the heart with her good hand. She carefully drew it out, cradling it to her chest. As soon as it had left the trunk, the last few leaves released their hold on the branches and fell to the ground like gently drifting snowflakes. The bark of Nammu seemed to lose its shine, becoming grey and lifeless. A stone tree in a frozen wilderness.

Silence enveloped them. Even the constant whistle of the north wind seemed to still. There was a sense that a momentous event had just happened. A change in the world that rippled through every atom.

‘Well,’ said Elowen when the stillness had gone on for a few minutes. ‘Perhaps we should start walking home. We have quite a long journey ahead of us.’

‘I can carry you all,’ said Embla. ‘If someone holds the heart.’

‘Give it to Lug,’ said Elowen. ‘I think he needs it most.’

Liska looked hard at the worm caller and realised he had been very quiet since the battle. She noticed that his fingertips had turned dark. Perhaps the frostbite was setting in and causing him pain? She was about to ask when he began to sob. Big racking gasps that made his whole body shake as tears ran down his face.

‘I don’t deserve to hold it!’ he cried. ‘I don’t deserve to even be here! I’m useless! A failure!’

‘What are you talking about?’ Liska put a paw on his knee but he shook it off.

‘I can’t do anything!’ he wailed. ‘Every time I’ve tried to help, it just goes wrong. All I can do is throw worms at people. Worms! How is that meant to do anything?’

‘Lug . . . that’s not true. You’re just as important as any of us—’