Polly and Buster continue down the long narrow tunnel, following the steel railway tracks that stretch endlessly ahead of them. The stones light the way and keep Polly’s mind clear from the darkness of the mines.

Buster has stopped talking now, and Polly concentrates hard on listening out for any sounds other than the drip, drip, dripping of water and the echo of their nervous breathing. On and on they walk, with no idea where they are going and the tunnel growing darker and narrower with each step.

Polly tries to picture what these deserted mines would have been like when they were full of workers. She imagines them noisy with rackety wooden carriages overflowing with rocks and precious stones, hauled to the surface by strong monsters, heaving and panting with effort.

Suddenly Buster grips Polly’s hand and pulls her to a stop. ‘Did you hear that?’ he whispers.

Polly cranes her head forward to listen into the dark. She hears a low rushing sound rolling up through the tunnel, like wind singing through the trees or a distant roaring ocean. The hairs on her arms begin to prickle.

‘What is it?’ Buster whispers again.

‘Shhh …’ Polly says, and puts a finger to her lips. The sound comes again, a little louder this time. She grips Buster’s paw tightly and she can feel him shrink a little in fear.

Buster jiggles on the spot. ‘Oh, Polly, oh Polly, oh Polly,’ he murmurs. ‘I don’t like this. I don’t like this at all!’

Polly holds the pouch of stones up high and peers into the darkness. The sound comes again. This time it is louder and clearer and Polly can even make out some words.

‘Go away! Go awaaaaaaaay!’ it howls, and Buster pulls hard at Polly’s hand.

‘Stop it!’ Polly whispers to Buster. ‘Who’s there?’ she calls out into the dark.

The voices come again. ‘We are the ghosts of the Hollow Valley Mines …’ they croon. ‘Scary, scary ghosts. Run away, little children! Run away!’

‘You heard them!’ Buster yelps, tugging at Polly’s hand, but Polly stands firm. Her heart is pounding and her legs are wobbly but she takes a deep breath and allows the warmth of the stones to fill her belly with courage.

‘Show yourselves!’ she demands. ‘We’re not scared of ghosts, are we, Buster?’

Buster stares at Polly like she’s gone completely nuts.

Polly widens her eyes at him. ‘Are we, Buster?’ she says, firmly.

‘Nope!’ Buster squeaks. ‘Nope! Not ghosts. Definitely not scared of ghosts!’

The voice comes again, louder and angrier. ‘Well, you should be! We are scary ghosts. Very scary ghosts! You should run away while you can! Go home and never come back here again!’

‘Why?’ shouts Polly, sounding braver than she feels. ‘What are you going to do to us?’

There is a pause, and Polly hears an awkward mumbling while the ghosts whisper among themselves. Another spooky voice pipes up. ‘We are going to scaaaaare you! That’s what we’re going to do!’ And as if to prove it, the voice finishes with a long, particularly scary, ‘Hooooooooooooo!!!’

Polly frowns. ‘Well, you’d do a much better job of scaring us if we could see you,’ she snorts.

The ghosts go quiet. Then, one by one, they slip out from the rocky tunnel walls and hover in front of Polly and Buster. Three shimmering, misty figures shake their ghostly arms at them and pull their scariest faces.

But somehow, in the bright light of the magic stones, it is hard for them to seem scary at all. The smallest one is trying so hard to pull a scary face it actually makes Polly laugh. Even Buster’s tight grip on Polly’s hand seems to relax a little.

‘OK, not scared,’ says Polly, and she makes to move past them, pulling Buster along behind her.

The ghosts look at each other in alarm. ‘Noooo!’ they shriek. ‘You must not go further! Turn back! Turn back!’

‘Or what?’ says Polly.

‘Or, or …’ they look at each other anxiously, ‘we’ll scaaaare you!’ They spin around Polly and Buster and shake their ghostly fingers right in Polly’s face.

But Polly keeps walking. Up ahead she sees a dark hollow in the side of the tunnel wall. The ghosts notice that she has seen it and spin around her more urgently.

‘Go back! Go back!’ they shriek. ‘This is no place for children. Go home! Run away. Whatever you do, don’t go into that chaaaaaamberrrr!’

Buster shrugs. ‘Maybe they know what they’re talking about?’ he says nervously. ‘That’s a pretty spooky-looking chamber.’

Polly holds out the magic stones. They are gleaming brighter than ever. ‘Buster! Don’t you understand? There’s something in there the ghosts don’t want us to see. But look at the stones! Look how brightly they are shining! The stones want me to go into that chamber, so I’m going in! Are you coming with me, or not?’

Buster sways a little from side to side, and chews his bottom lip.

‘Buster?’ Polly says.

‘Of course I’m coming!’ he says gruffly. ‘We’re doing this together, aren’t we?’

Polly smiles and pushes past the ghosts to step into the chamber.