Buster takes Polly’s hand and swings it in his paw. They have been walking a long, long way up the steep slope of the dark, gloomy tunnel, feeling their way back along the walls in the fading light of the stones. Polly feels sure the entrance can’t be far off now, and she can feel Buster’s pace quickening.

‘What’s the first thing you’re going to do when you get home?’ Buster asks her.

‘Have a hot bath,’ says Polly. She has begun to shiver from the cold. ‘Actually, no. Hug my mum, then have a hot bath.’

‘I’m going to hug my mum, then eat a whole plate of jamcakes,’ Buster says. ‘Hot ones with extra dibblecream on top.’

‘Then have a bath?’ Polly giggles.

‘Why?’ says Buster. ‘Do I smell?’

‘Only like a monster who hasn’t washed in two days. And slept in his clothes.’

‘That’s not a bad smell, is it?’ Buster asks, lifting up a hairy arm and smelling underneath it.

‘No!’ says Polly, giggling. ‘I love the smell of dirty monster.’

Buster elbows Polly. She tumbles against the wall.

‘Hey! Don’t you think it’s hard enough walking in the dark without you knocking me over?’ She laughs and walks a little further. Suddenly she stops and Buster bumps into her. ‘Look, Buster! Up ahead. Is that light?’ She squints into the darkness. ‘Do you think it’s the entrance?’

Buster pauses to squint, too. ‘Maybe?’ he says hopefully.

‘Wait!’ says Polly, frowning and pulling Buster close. ‘Can you hear that?’ She gets a familiar funny feeling in her tummy, and the stones begin to grow warm in her hand again. ‘Hello? Is someone there?’ Polly calls out.

‘It better not be ghosts again!’ Buster mumbles, rolling his eyes.

But before Polly has the chance to answer, a blinding flash of turquoise lights up the tunnel. Polly and Buster are thrown backwards onto the hard rocky ground. There is an earsplitting crack and the tunnel rumbles around them. Buster dashes to cover Polly just as an avalanche of rocks falls down on them from the crumbling walls. He pushes away as many as he can, but they are falling thick and fast.

Again and again the rocks smash against Buster’s broad furry back, but he uses all his strength to keep them from hitting Polly. The noise in the tunnel is deafening.

Eventually the cascade slows until only dust and pebbles settle on the pile of rubble. Buster carefully pushes the many heavy rocks away.

‘Ow!’ he says, dusting off his fur.

Polly sits up, blinking and dust-covered. She has a graze on her cheek, but nothing like the big welts Buster has across his back.

‘Buster!’ she coughs. ‘Are you OK?’

Her heart begins to race. She sniffs the air in case the avalanche has woken the gorvan, but there is no sign or smell of it. She breathes out in relief. The gorvan must be far enough and deep enough underground for it not to have been disturbed.

‘I’m OK,’ Buster says gruffly, but Polly can see him wince when he tries to stand.

Polly checks all her limbs. She is in one piece. ‘Mangy mushrooms!’ she says. ‘I would have been crushed if it wasn’t for you, Buster. What was that? An earthquake?’

Buster shakes his head and frowns. ‘I don’t think so,’ he says, pointing to something behind Polly. ‘In fact, I’d say it was more of a witchquake.’

Polly gasps and scrambles to stand up. She looks to where Buster is pointing. A little distance away from all the debris, lying on the tunnel floor, is Malorie – Mrs Halloway’s daughter. Her foot is trapped under a rock and she cries out in pain.

‘Malorie Halloway!’ Polly says furiously. ‘That was you? I can’t believe it! You did a spell to make those rocks fall! Why would you do such a thing?’

Malorie begins to cry. ‘My mother sent me in here. The spell wasn’t meant to hurt you, I promise. Just block you in here.’

Polly sees Mrs Halloway’s fancy wand, crushed and broken under the rocks beside Malorie. ‘And then what?’ she shouts. ‘We’d be trapped in here and left to die?’

Malorie begins to cry harder. ‘I didn’t know you’d be in here, too, Polly. My mother told me it was just Buster. And she told me he’s a dangerous monster who would hurt me and lots of other witches too, and that I was doing the right thing. That’s what she told me, Polly!’

‘You Know that’s not true, Malorie!’

Polly yells, even louder than before.

She can feel the rage steaming up through her chest and takes some gulps of the dusty air to try and calm down. ‘You know Buster is my friend. That he’s always been my friend. Why would I be friends with a monster who is dangerous?’

Malorie sobs and sobs. ‘I’m sorry, Polly! I really am. Oh, please help me. I can’t move and my leg is really hurting!’

Buster squirms beside Polly in discomfort. She knows he hates seeing anyone upset or in pain and she can feel him shifting anxiously from one foot to another.

‘Sorry?’ spits Polly, furiously. ‘Sorry? I think it’s a bit late for that!’

‘You don’t know what it’s like living with my mother,’ Malorie cries. ‘I didn’t have a choice.’

‘Of course you had a choice!’ Polly hisses. ‘You always have a choice. And you chose to do the wrong thing, Malorie. And so for that we are going to leave you here. If your precious mother loves you so much then she can come in here and rescue you. But think about it, Malorie. Don’t you think it’s a little odd she sent her daughter into these dangerous, scary mines rather than going in herself?’

Polly pulls Buster’s paw for him to follow her as she clambers over the rocks towards the entrance. ‘Don’t worry, Malorie. We’ll tell your mother where you are. On our way out!’

As they stumble closer, Polly can see Malorie’s face is bleached white with pain. Her eyes are squeezed shut and Polly almost feels sorry for her, but then she allows her anger to fill her again. Deidre Halloway and her daughter need to be taught a lesson once and for all, she decides, and pulls at Buster’s paw.

But he won’t come.

‘Buster,’ she hisses. ‘Come on!’

Buster rocks anxiously from side to side. ‘We can’t just leave her here,’ he murmurs, his face twisting with concern.

‘Yes. We. Can!’ Polly insists, jerking at Buster’s paw. ‘She wanted to hurt you, Buster. Maybe even kill you!’

But he won’t budge.

‘Polly!’ he says, so firmly that she drops his paw in surprise. She has never heard him raise his voice before. ‘You are my bestest best friend in the whole wide world and probably the cleverest and bravest witch I know. I would usually do anything you ask me. But not this. Just because Malorie did the wrong thing, doesn’t mean we should, too. We are not bad, Polly. We are good. Remember?’ Polly sighs deeply and slumps forward. She feels tired and achey and dirty and she just wants to be home. But she knows Buster is right. There is no other heart she knows that is as good and true. And she knows there are times when she has done the wrong thing herself, and hurt others without meaning to. She is no different, really, to Malorie.

‘All right!’ she grumbles angrily. ‘You can lift the rock off her foot then. But that’s all! She has to walk back by herself. You are not to carry her, all right? Even if she is hurt!’

But it turns out Malorie can barely stand, let alone walk, so dear, sweet Buster hauls her up over his bruised shoulders and they limp slowly back towards the pale, grey light, each step taking them closer to home.