Still, no time to moon about. Stairways did not tend to remain deserted for long, especially during a siege. Who could tell how many bloodthirsty troopers waited behind each door, eager for a fairy head to add to their stuffed trophy wall.

Mulch climbed carefully, taking nothing for granted. Even solid oak creaked. He stuck to the borders, avoiding the carpet inlay. The dwarf knew from conviction number eight how easy it was to conceal a pressure pad beneath the deep shag of some antique weave.

He reached the landing with his head still attached to his shoulders. But there was another problem quite literally brewing.

Dwarf digestion, due to its accelerated rate, can be quite explosive.

The loosely packed soil on the Fowl estate was very well aerated and a lot of that air had entered Mulch's tubes along with the soil and minerals. Now the air wanted to get out.

Dwarf etiquette dictated that gas be passed while still in the tunnel, but Mulch didn't have time for manners. Now he regretted not taking a moment to get rid of the gas while he was in the cellar. The problem with dwarf gas was that it couldn't go up, only down.

Imagine, if you will, the catastrophic effects of burping while digesting a mouthful of clay. Total system back-up. Not a pretty sight. Thus dwarf anatomy ensured that all gas was passed below, actually aiding in the expulsion of unwanted clay. Of course, there's a simpler way of putting this, but that version can only be read in the adult book.

Mulch wrapped his arms around his stomach. He'd better get out of the open. A blowout on a landing like this could take out the windows. He shuffled along the corridor, skipping through the first doorway he encountered.

More cameras. Quite a lot of them, in fact. Mulch studied the lenses' sweep. Four were surveying the general floorspace, but another three were fixed.

'Foaly? You there?' whispered the dwarf.

'No!' The typical sarcastic reply. 'I have much better things to do than worry about the collapse of civilization as we know it.'

'Yes, thank you. Don't let my life being in danger interrupt your merriment.'

'I'll try not to.'

'I have a challenge for you.'

Foaly was instantly interested. 'Really? Go on.'

Mulch pointed his gaze at the recessed cameras, half hidden in the swirling architrave. 'I need to know where those three cameras are pointing. Exactly.'

Foaly laughed.

'That's not a challenge. Those old video systems emit faint ion beams. Invisible to the naked eye, of course, but not with your iris-cam.'

The hardware in Mulch's eye flickered and sparked.

'Oww!'

'Sorry. Small charge.'

'You could have warned me.'

'I'll give you a big kiss later, you baby. I thought dwarfs were tough.'

'We are tough. I'll show you just how tough when I get back.'

Root's voice interrupted the posturing. 'You won't be showing anyone anything, convict, except perhaps where the toilet is in your cell. Now, what do you see?'

Mulch looked at the room again through his ion-sensitive eye.

Each camera was emitting a faint beam, like the last evening sunrays.

The rays pooled on a portrait of Artemis Fowl Senior.

'Not behind the picture. Oh, please.'

Mulch placed his ear against the picture glass. Nothing electrical. Not alarmed then. Just to be sure, he sniffed the frame's edge. No plastic or copper. Wood, steel and glass. Some lead in the paint. He curled a nail behind the frame and pulled. The picture came away smoothly, hinged on the side. And behind it. A safe.

'It's a safe,' said Foaly.

'I know that, you idiot. I'm trying to concentrate here! If you want to help, tell me the combination.'

'No problem. Oh, by the way, there's another little shock coming. Maybe the big baby would like to suck his thumb for comfort.'

'Foaly. I'm going to…Owww!'

'There. That's the X-ray on.'

Mulch squinted at the safe. It was incredible. He could see right into the works. Tumblers and catches stood out in shadowy relief. He blew on his hairy fingers and twisted the combination dial. In seconds the safe lay open before him.

'Oh,' he said, disappointed.

'What is it?'

'Nothing. Just human currency. Nothing of value.'

'Leave it,' ordered Root. 'Try another room. Get going.'

Mulch nodded. Another room. Before his time ran out. But something was niggling at him. If this guy was so clever, why did he put the safe behind a painting? Such a clichй. Totally against form. No.

Something wasn't right here. They were being duped somehow.

Mulch closed the safe, swinging the portrait back into position. It swung smoothly, weightless on the hinges. Weightless. He swung the picture out again. And back in.

'Convict. What are you doing?'

'Shut up, Julius! I mean, quiet a moment, Commander.'

Mulch squinted at the frame's profile. A bit thicker than normal. Quite a bit thicker. Even taking the box frame into account. Five centimetres. He ran a nail down the heavy cartridge backing and stripped it away to reveal…

'Another safe.'

A smaller one. Custom-made, obviously.

'Foaly. I can't see through this.'

'Lead-lined. You're on your own, burglar boy. Do what you do best.'

'Typical,' muttered Mulch, flattening his ear to the cold steel.

He twirled the dial experimentally. Nice action. The clicks were muted by the lead, he would have to concentrate. The upside was that something this thin could have only three tumblers at the most. Mulch held his breath and twisted the dial, one cog at a time. To the normal ear, even with amplification, the clicks would have seemed uniform. But to Mulch, each cog had a distinctive signature and when a ratchet caught, it was so loud as to be deafening.

'One,' he breathed.

'Hurry it up, convict. Your time is running out.'

'You interrupted to tell me that? I can see now how you made commander, Julius.'

'Convict. I'm going to…'

But it was no use. Mulch had removed his earpiece, slipping it into his pocket. Now he could devote his full attention to the task at hand.

'Two.'

There was noise outside. In the hall. Someone was coming. About the size of an elephant by the size of it. No doubt this was the man mountain that had made mincemeat of the Retrieval Squad.

Mulch blinked a bead of sweat from his eye. Concentrate.

Concentrate. The cogs clicked by. Millimetre by millimetre. Nothing was catching. The floor seemed to be hopping gently, though he could be imagining it.

Click, click. Come on. Come on. His fingers were slick with perspiration, the dial slipping between them. Mulch wiped them on his jerkin.

'Now, baby, come on. Talk to me.'

Click. Thunk.

'Yes!'

Mulch twisted the handle. Nothing. Still an obstruction. He ran a fingertip over the metal face. There. A small irregularity. A micro keyhole. Too small for your average lock pick. Time for a little trick he'd learned in prison. Quickly though, his stomach was bubbling like stew in the oven, and the footsteps were getting closer.

Selecting a sturdy chin hair, Mulch fed it gently into the tiny hole. When the tip reappeared, he pulled the root from his chin. The hair immediately stiffened, retaining the shape of the lock's interior.

Mulch held his breath and twisted. Smooth as a goblin's lie, the lock opened. Beautiful. At moments like these, it was almost worth all the jail time.

The kleptomaniac dwarf swung back the little door. Beautiful work. Almost worthy of a fairy forge. Light as a wafer. Inside was a small chamber. And in the chamber was…

'Oh, gods above,' breathed Mulch.

Then things came to a head rather rapidly. The shock that Mulch had experienced communicated itself to his bowels, and they decided the excess air had got to go. Mulch knew the symptoms. Jelly legs, bubbling cramps, wobbly behind. In the seconds remaining to him, he snatched the object from the safe and, leaning over, he clasped his knees for support.