‘Why are there so many bones down here?’ I called back to the Spook. ‘Do they belong to prisoners who tried to escape from the cells?’

‘A few maybe,’ he replied. ‘But the buggane regurgitates some of the bones it’s swallowed after feeding.’

I shuddered, realizing that the foot and the skull had spent time in the buggane’s stomach.

For about five minutes we made good progress, but then we encountered a problem. There were thick tree roots ahead of us, completely blocking the main tunnel. Another tunnel went off at an angle, heading downwards. It was new and freshly dug; I didn’t like the look of it one bit.

‘This is the buggane’s doing,’ I said. ‘What now?’ ‘To reach the hollow tree we need to get past those roots somehow,’ Alice replied.

‘We could dig round it with our staffs but it’ll take ages. I know a better way,’ I said, turning to look past Alice and Adriana. ‘There are roots blocking our way!’ I shouted to the Spook. ‘Reverse back down the tunnel a bit. We need to give the dogs room to work. Claw! Blood! Bone!’

The dogs came squeezing past us eagerly as the others retreated. I dug at the earth beside the roots with my hands and pointed ahead. Soon the three wolfhounds were burrowing away enthusiastically, throwing earth backwards with their paws. In fact we got two tunnels instead of one because Claw worked to the left while Blood and Bone dug their own tunnel to the right.

The latter was the larger excavation, and the Spook and I widened it with the blades of our staffs until we could squeeze through.

At last we were moving again. I began to feel optimistic about escaping from the hollow tree. It was dangerous, but if anyone could find the secret way through the bone-yard it was Alice.

But soon we encountered another problem, this one much worse than before. We found the passage ahead completely blocked with hard-packed earth. Once again a new tunnel had been excavated by the buggane; one that headed sharply downhill.

The Spook crawled forward to join me, shaking his head. ‘We could try digging again, but the whole tunnel might have caved in behind,’ he said. ‘I don’t like it, lad. It’s almost as if we’re being herded like sheep. Forced downwards to where someone wants us to be.’

‘The buggane?’ I asked.

‘Maybe – but it could be acting for Lizzie. By now she’ll probably know that we’ve escaped the tower. We either retreat the way we came or go down there,’ he said, pointing towards the new tunnel.

‘If we go back, they’ll be waiting. This time Lizzie will put us all in the dungeons,’ I said.

The Spook shrugged. ‘Then we must go on. I’ll take the lead now, lad – who knows what we’re about to face?’ And with those words he set off, crawling along the tunnel.

The descent got steeper and I was growing increasingly uneasy. I sensed danger ahead.

Then the passage began to widen, and the Spook got to his feet, lifting the lantern. Moments later, we saw a vast space ahead, the walls so distant that the light couldn’t reach them. We were at the entrance to a huge cavern.

Even the dogs were silent. They stayed behind us, unwilling to venture in any further and explore. Perhaps they felt as we did: a sense of awe; a feeling that we faced something totally new and beyond our experience.

‘I didn’t expect this,’ said the Spook, his voice hardly more than a whisper. ‘I think I know what this place is. I thought it was just a myth – a story. But it’s real…’

‘What’s real?’ I asked. ‘What is it?’

But the Spook just muttered something to himself and didn’t answer my question.

‘This ain’t been done by the buggane,’ said Alice. ‘Take ten lifetimes to make a burrow this big, even if its claws could dig through rock.’

‘This was here already and the buggane chanced upon it,’ my master said.

‘Or maybe it knew about it,’ said Adriana, emerging from the dark tunnel. ‘Maybe it deliberately chose to build its labyrinth here because it knew about this cavern.’

‘But what would it want something so big for?’ I asked, thinking aloud.

‘Well, as I’ve already told you, lad,’ said the Spook, ‘a buggane takes the animus, the life force of a human, and stores it at the centre of its labyrinth; it was working with the shaman, so it needed lots of space. But this is immense – far beyond what it should need.’

‘What does it use the animas for?’

‘Well, we know that for a shaman they’re a source of magical power, giving him control over animals and allowing him to project his spirit far from his body. But as for the buggane, nobody’s ever had a real conversation with such a creature. It whispers, it threatens, then sucks out the animus and kills its victim, but we don’t know why. The shaman, Lord Barrule, would know more, but he’s dead now…

‘Well, lad,’ my master went on, ‘you asked me what this place is, and I’ll tell you. It’s something I didn’t think I’d live to see. Something I’ve only heard tell of. It’s known as the “Grim Cache” after its creator, and it’s the largest source of animism in the world. It was first accumulated by a shaman called Lucius Grim many centuries ago. It’s said that he was able to project his spirit into the dark itself, but eventually his soul was consumed by a daemon. This is his legacy, no doubt added to by other shamans since – the latest being Lord Barrule. Anyway, let’s move on – but keep close to the cavern wall. Who knows – we might find another way out.’

The Spook led the way, the dogs following behind, still subdued. Underneath our feet soft mud gave way to rock. It wasn’t long before Alice gasped in astonishment – she had noticed something ahead. ‘Something up there,’ she said. ‘I can see lights moving. Don’t like the look of ’em.’

We looked up to where she was pointing. Tiny points of yellow light like distant stars were combining to form intricate patterns, moving more like a shoal of fish than a flock of birds. I tried to count them; it was difficult, but I thought there were seven. Suddenly one detached itself from the rest and floated down towards us. As it approached, I saw that it was a glowing sphere.

‘Fire elementals!’ cried Alice. ‘Just like the ones we saw in Greece…’

We’d faced different types of fire elemental there, ranging from fiery orbs to asteri, which looked like five-pointed stars. They were all deadly and could burn you to cinders in moments. They’d certainly done for Bill Arkwright.

However, the Spook shook his head. ‘Nay, girl, whatever they are, they won’t be fire elementals. It’s too damp in this cavern. In fact this whole island has a wet climate very similar to the County. It’s no place for entities like that. They couldn’t survive here.’

As if to prove him right, rather than attacking us, the glowing orb backed away, drifting upwards, and once more became a distant point of light, having rejoined its companions in their strange dance. It was as if it had taken a close look at us and decided we were of no interest.

It was then that the Spook first noticed that Alice was carrying a book. ‘Where did you get that, girl?’ he demanded with a frown. ‘Did it belong to the shaman?’

Alice nodded. ‘It’s his notebook. Brought it so that Lizzie wouldn’t get her hands on it and learn new things about the dark. Best that we have it, don’t you think?’

My master looked unconvinced but said nothing, and we continued to follow the curved wall of the cavern. Once again it was Alice who brought us to a halt. She sniffed loudly, three times. ‘There’s something ahead and coming this way,’ she warned. ‘Something from the dark…’

No sooner had she said that than all three dogs began to growl; they had sensed the danger too. We held our lanterns aloft and saw a figure approaching us.

‘It’s the abhuman,’ Alice said as he moved into the arcs of light.

She was right. Horn was alone. The two holes in his ears where they’d attached the chains still appeared inflamed, and his blind, milky-white eyeballs moved as if he were assessing each one of us in turn.