He hurried away, with Cheery trailing behind him.

Dee led the way through dark tunnels. When the opera began it was a whisper far away, like the sea in an ancient shell.

Eventually they stopped at the edge of a canal, its waters lapping at the darkness. A small boat was tethered there, with a waiting guard. Dee urged them into it.

'It is important that you understand what you are seeing, your grace,' said Dee.

'Practically nothing,' said Vimes. 'And I thought I had good night vision.'

There was a clink in the gloom, and then a lamp was lit. The guard was punting the boat under an arch and into a small lake. Apart from the tunnel entrance, the walls rose up sheer.

'Are we at the bottom of a well?' said Vimes.

'That is quite a good way of describing it.' Dee fished under his seat. He produced a curved metal horn and blew one note which echoed up the rock walls.

After a few seconds another note floated down from the top. There was a clanking, as of heavy, ancient chains.

'This is quite a short lift compared to some up in the mountains,' said Dee, as an iron plate ground across the entrance, sealing it. 'There's one half a mile high that will take a string of barges.'

Water boiled beside the boat. Vimes saw the walls begin to sink.

'This is the only way to the Scone,' said Dee behind him.

Now the boat was rocking in the bubbling water and the walls were blurred.

'Water is diverted into reservoirs up near the peaks. Then it is simply a matter of opening and closing sluices, you see?'

'Yes,' mumbled Vimes, experiencing vertigo and seasickness in one tight green package.

The walls slowed. The boat stopped shaking. The water lifted them smoothly over the lip of the well and into a little channel, where there was a dock.

'Any guards below?' Vimes managed, stepping out on to the blessedly solid stone.

'There are usually four,' said Dee. 'For tonight I... arranged matters. The guards understand. No one is proud of this. I must tell you, I disapprove most strongly of this enterprise.'

Vimes looked around the new cave. A couple of dwarfs were standing on a lip of stone that overlooked what was now a placid pool. By the look of it, they were the ones who operated the machinery.

'Shall we proceed?' said the dwarf.

There was a passage leading off the cave, which rapidly narrowed. Vimes had to bend almost double along one length. At one point metal plates clanked under his feet, and he felt them shift slightly. Then he was standing almost upright again, passing under another arch, and there...

Either the dwarfs had cut into a huge geode or they had with great care lined this small cave with quartz crystals until every surface reflected the light of the two small candles that stood on pillars in the middle of the sandy floor. The effect dazzled even Vimes after the darkness of the tunnels.

'Behold,' said Dee gloomily, 'where the Scone should be.'

A round flat stone, midway between the candles and only a few inches high, clearly held nothing.

Behind it water bubbled up in a natural basin and split into two streams that flowed around the stone and disappeared again into another stone funnel.

'All right,' said Vimes. 'Tell me everything.'

'It was reported missing three days ago,' said Dee. 'Dozy Longfinger found it gone when he went in to replace the candles.'

'And his job is...'

'Captain of the Candles.'

Ah.

'It's a very responsible position.'

'I've seen the chandeliers. And how often does he go in there?'

'He went in there every day.'

'Went?'

'He no longer holds the position.'

'Because he's a prime suspect?' said Vimes.

'Because he's dead.'

'And how did that happen?' said Vimes, slowly and deliberately.

'He... took his own life. We're certain of this because we had to break down the door of his cave. He'd been Captain of the Candles for sixty years. I think he couldn't bear the thought of suspicion falling on him.'

'To me he does sound a likely suspect.'

'He did not steal the Scone. We know that much.'

'But the robes you people wear could hide practically anything. Was he searched?'

'Certainly not! But... I'll demonstrate,' said Dee. He walked off along the narrow, metalfloored corridor. 'Can you see me, your excellency?'

'Yes, of course.'

The floor rattled as Dee came back. 'Now this time I'll carry something... Your helmet, if you please? Just for the demonstration.'

Vimes handed it to him. The Ideas Taster walked back down the corridor. When he was halfway a gong boomed and two metal grilles dropped down out of the ceiling. A few seconds after that guards appeared at the far grille, peering in suspiciously.

Dee said a few words to them. The faces vanished. After a while the grilles rose slowly.

'The mechanism is complex and quite old, but we keep it in good working order,' he said, handing Vimes his helmet. 'If you weigh more going out than going in, the guards will want to know why. It's unavoidable, it is still accurate to within a few ounces, and does not violate privacy. The only way to beat it would be to fly. Can thieves fly, your excellency?'

'Depends on which sort,' said Vimes absently. 'Who else goes in there?'

'Once every six days the chamber is inspected by myself and two guards. The last inspection was five days ago.'

'Does anyone else go in there?' said Vimes. He noticed that Cheery had picked up a handful of the off-white sand that formed the floor of the Scone Cave and was letting it run between her fingers.

'Not lately. When the new king is crowned, of course, the Scone will often be brought forth for ceremonial purposes.'

'Do you only get that white sand in here?'

'Yes. Is that important?'

Vimes saw Cheery nod. 'I'm not... sure,' he said. 'Tell me, what intrinsic value has the Scone?'

'Intrinsic? It's priceless!'

'I know it's valuable as a symbol, but what is its value in itself?'

'Priceless!'

'I'm trying to work out why a thief might want to steal it,' said Vimes, as patiently as he could.

Cheery had lifted up the flat round stone and was looking underneath it. Vimes pursed his lips.

'What is... she doing?' said Dee. The pronoun dripped with distaste.

'Corporal Littlebottom is looking for clues,' said Vimes. 'They are what we call signs, which may help us. It's a skill.'

'Would this letter speed your search?' said Dee. 'It has writing on it. That is what we call... signs, which may help you.'

Vimes looked at the proffered paper. It was brown and quite stiff, and covered in runes.

'I, er, can't read those,' he said.

'It's a skill,' said Dee solemnly.

'I can, sir,' said Cheery. 'Allow me?'

She took the paper and read it. 'Er, it appears to be a ransom note, sir. From... the Sons of Agi Hammerthief. They say they have the Scone and will... They say they'll destroy it, sir.'

'Where's the money?' said Vimes.

'They say Rhys must renounce all claim to be Low King,' said Dee. 'There are no other conditions. The note turned up on my desk. But everyone puts paperwork on my desk these days.'

'Who are the Sons of Agi Hammerthief?' said Vimes, looking at Dee. 'And why didn't you tell me about this before?'

'We don't know. It's just a made-up name. Some malcontents, we assume. And I was told you would ask me questions.'

'But this isn't a real crime any more, is it?' said Vimes. 'This is politics. Why can't the King just renounce all claim, get the Scone back, and then say he had his fingers crossed? If it's done under duress—'

'We take our ceremonies seriously, your excellency. If Rhys renounces the throne, he cannot change his mind next day. If he allows the Scone to be destroyed, then the kingship has no legitimacy and there will—'