Nanny stopped where the path forked, and then pointed.
'I reckon she's gone this way. Hold on-'
She thrust out an arm. Stone groaned, and a slab of roof thudded down, throwing up spray and pebbles.
'So we'll just have to climb over this bit, then,' Nanny went on, in the same matter-of-fact tone of voice.
'Something's trying to push us out,' said Agnes.
'But it won't,' said Nanny. 'And I don't think it'll harm us.'
'That was a big slab!' said Agnes.
'Yeah. But it missed us, didn't it?'
There was an underground river further on, sheer white water blurred with speed. It poured around and almost over a dam of driftwood, topped by an inviting long log.
'Look, this isn't safe for the baby!' said Agnes. 'Do you both see that? You're her mother, Magrat!'
'Yes, I know, I was there,' said Magrat, with infuriating calm. 'But this doesn't feel,unsafe. Granny's here somewhere.'
'That's right,' said Nanny. 'Really close now, I think.'
'Yes, but she can't control rivers and rocks-' Agnes began.
'Here? Dunno. Very... responsive place, this.'
They inched their way across the log, passing the baby from one to the other.
Agnes leaned against the stone wall. 'How much further?'
'Well, technic'ly a few inches,' said Nanny. 'That's helpful to know, isn't it?'
'Is it just me,' said Magrat, 'or is it getting warmer?'
'Now that,' said Agnes, pointing ahead, 'I don't believe.'
At the end of a slope a crevasse had opened in the rock. Red light spilled out. As they stared at it, a ball of flame rolled up and burst across the ceiling.
'Oh deary deary me,' said Nanny, who had taken a turn to carry the baby. 'An' it's not even as if there's any volcanoes anywhere near here. What can she be thinking?' She headed purposefully towards the fire.
'Careful!' Agnes shouted. 'Perdita says it's real!'
'What's that got to do with the price of fish?' said Nanny, and stepped into the fire.
The flames snapped out.
The other two stood in the chilly, damp gloom.
Magrat shuddered. 'Nanny, you are carrying the baby.'
'The harm you come to here is what you brings with you,' said Nanny. 'And it's Granny's thoughts that are shaping this place. But she wouldn't raise a hand to a child. Couldn't do it. Hasn't got it in her.'
'This place is reacting to what she's thinking?' said Agnes.
'I reckon so,' said Nanny, setting off again.
'I'd hate to be inside her head!'