Sergeant Colon had given him a badge. The Librarian turned it round and round in his big gentle hands, nibbling at it.

It wasn't that the city suddenly had a king. Orangs are traditionalists, and you couldn't get more traditional than a king. But they also liked things neat, and things weren't neat. Or, rather, they were too neat. Truth and reality were never as neat as this. Sudden heirs to ancient thrones didn't grow on trees, and he should know.

Besides, no-one was looking for his book. That was human priorities for you.

The book was the key to it. He was sure of that. Well, there was one way to find out what was in the book. It was a perilous way, but the Librarian ambled along perilous ways all day.

In the silence of the sleeping library he opened his desk and removed from its deepest recesses a small lantern carefully built to prevent any naked flame being exposed. You couldn't be too careful with all this paper around . . .

He also took a bag of peanuts and, after some thought, a large ball of string. He bit off a short length of the string and used it-to tie the badge around his neck, like a talisman. Then he tied one end of the ball to the desk and, after a moment's contemplation, knuckled off between the bookshelves, paying out the string behind him.

Knowledge equals power. . .

The string was important. After a while the Librarian stopped. He concentrated all his powers of librarianship.

Power equals energy . . .

People were stupid, sometimes. They thought the Library was a dangerous place because of all the magical books, which was true enough, but what made it really one of the most dangerous places there could ever be was the simple fact that it was a library.

Energy equals matter. . . .

He swung into an avenue of shelving that was apparently a few feet long and walked along it briskly for half an hour.

Matter equals mass.

And mass distorts space. It distorts it into polyfractal L-space.

So, while the Dewey system has its fine points, when you're setting out to look something up in the multidimensional folds of L-space what you really need is a ball of string.

Now the rain was trying hard. It glistened off the flagstones in the Plaza of Broken Moons, littered here and there with torn bunting, flags, broken bottles and the occasional regurgitated supper. There was still plenty of thunder about, and a green, fresh smell in the air. A few shreds of mist from the Ankh hovered over the stones. It would be dawn soon.

Vimes's footsteps echoed wetly from the surrounding buildings as he picked his way across the plaza. The boy had stood here.

He peered through the mist shreds at the surrounding buildings, getting his bearings. So the dragon had been hovering-he paced forward-here.

“And,” said Vimes, “this is where it was killed.”

He fumbled in his pockets. There were all sorts of things in there-keys, bits of string, corks. His finger closed on a stub end of chalk.

He knelt down. Errol jumped off his shoulder and waddled away to inspect the detritus of the celebration. He always sniffed everything before he ate it, Vimes noticed. It was a bit of a puzzle why he bothered, because he always ate it anyway.

Its head had been about, let's see, here.

He walked backwards, dragging the chalk over the stones, progressing slowly over the damp, empty square like an ancient worshipper treading a maze. Here a wing, curving away towards a tail which stretched out to here, change hands, now head for the other wing . . .

When he finished he walked to the centre of the outline and ran his hands over the stones. He realised he was half-expecting them to be warm.

Surely there should be something. Some, oh, he didn't know, some grease or something, some crispy fried dragon lumps. Errol started eating a broken bottle with every sign of enjoyment. “You know what I think?” said Vimes. “I think it went somewhere.”

Thunder rolled again.

“All right, all right,” muttered Vimes. “It was just a thought. It wasn't that dramatic.”

Errol stopped in mid-crunch.

Very slowly, as though it was mounted on very smooth, well-oiled bearings, the dragon's head turned to face upwards.

What it was staring at intently was a patch of empty air. There wasn't much else you could say about it.

Vimes shivered under his cape. This was daft.

“Look, don't muck about,” he said, “there's nothing there.”

Errol started to tremble.

“It's just the rain,” said Vimes. “Go on, finish your bottle. Nice bottle.”

A thin, worried keening noise broke from the dragon's mouth.

“I'll show you,” said Vimes. He cast around and spotted one of Throat's sausages, cast aside by a hungry reveller who had decided he was never going to be that hungry. He picked it up.

“Look,” he said, and threw it upwards.

He felt sure, watching its trajectory, that it ought to have fallen back to the ground. It shouldn't have fallen away, as if he'd dropped it neatly into a tunnel in the sky. And the tunnel shouldn't have been looking back at him.

Vivid purple lightning lashed from the empty air and struck the houses on the near side of the plaza, skittering across the walls for several yards before sinking out with a suddenness that almost denied that it had ever happened at all.

Then it erupted again, this time hitting the rimward wall. The light broke where it hit into a network of searching tendrils spreading across the stones.

The third attempt went upwards, forming an actinic column that eventually rose fifty or sixty feet in the air, appeared to stabilise, and started to spin slowly.

Vimes felt that a comment was called for. He said: “Arrgh.”

As the light revolved it sent out thin zigzag streamers that jittered away across the rooftops, sometimes dipping, sometimes doubling back. Searching.

Errol ran up Vimes's back in a flurry of claws and fastened himself firmly on his shoulder. The excruciating agony recalled to Vimes that there was something he should be doing. Was it time to scream again? He tried another “Arrgh”. No, probably not.

The air started to smell like burning tin.

Lady Ramkin's coach rattled into the plaza making a noise like a roulette wheel and pounded straight for Vimes, stopping in a skid that sent it juddering around hi a semicircle and forced the horses either to face the other way or plait their legs. A furious vision in padded leather, gauntlets, tiara and thirty yards of damp pink tulle leaned down towards him and screamed: “Come on, you bloody idiot!”

One glove caught him under his unresisting shoulder and hauled him bodily on to the box.

' 'And stop screaming!'' the phantom ordered, focusing generations of natural authority into four syllables. Another shout spurred the horses from a bewildered standing start to a full gallop.

The coach bounced away over the flagstones. An exploratory tendril of flickering light brushed the reins for a moment and then lost interest.

“I suppose you haven't got any idea what's happening?” shouted Vimes, against the crackling of the spinning fire.

“Not the foggiest!”

The crawling lines spread like a web over the city, growing fainter with distance. Vimes imagined them creeping through windows and sneaking under doors.

“It looks as though it's searching for something!” he shouted.

' 'Then getting away before it finds it is a first-class idea, don't you think?"

A tongue of fire hit the dark Tower of Art, slid blindly down its ivy-grown flanks, and disappeared through the dome of Unseen University's Library.

The other lines blinked out.

Lady Ramkin brought the coach to a halt at the far side of the square.

“What does it want the Library for?” she said, frowning.

“Maybe it wants to look something up?”

“Don't be silly,” she said breezily. “There's just a lot of books hi there. What would a flash of lightning want to read?”

“Something very short?”

“I really think you could try to be a bit more help.”

The line of light exploded into an arc between the Library's dome and the centre of the plaza and hung hi the air, a band of brilliance several feet across.

Then, hi a sudden rush, it became a sphere of fire which grew swiftly to encompass almost all the plaza, vanished suddenly, and left the night full of ringing, violet shadows.

And the plaza full of dragon.

Who would have thought it? So much power, so close at hand. The dragon could feel the magic flowing into it, renewing it from second to second, hi defiance of all boring physical laws. This wasn't the poor fere it had been given before. This was the right stuff. There was no end to what it could do, with power like this.

But first it had to pay its respects to certain people . . .

It sniffed the dawn air. It was searching for the stink of minds.

Noble dragons don't have friends. The nearest they can get to the idea is an enemy who is still alive.

The air became very still, so still that you could almost hear the slow fall of dust. The Librarian swung on his knuckles between the endless bookshelves. The dome of the Library was still overhead but then, it always was.

It seemed quite logical to the Librarian that, since there were aisles where the shelves were on the outside then there should be other aisles in the space between the books themselves, created out of quantum ripples by the sheer weight of words. There were certainly some odd sounds coming from the other side of some shelving, and the Librarian knew that if he gently pulled out a book or two he would be peeking into different libraries under different skies.

Books bend space and time. One reason the owners of those aforesaid little rambling, poky second-hand bookshops always seem slightly unearthly is that many of them really are, having strayed into this world after taking a wrong turning in their own bookshops in worlds where it is considered commendable business practice to wear carpet slippers all the time and open your shop only when you feel like it. You stray into L-space at your peril.

Very senior librarians, however, once they have proved themselves worthy by performing some valiant act of librarianship, are accepted into a secret order and are taught the raw arts of survival beyond the Shelves We Know. The Librarian was highly skilled in all of them, but what he was attempting now wouldn't just get him thrown out of the Order but probably out of life itself.

All libraries everywhere are connected in L-space. All libraries. Everywhere. And the Librarian, navigating by booksign carved on shelves by past explorers, navigating by smell, navigating even by the siren whisperings of nostalgia, was heading purposely for one very special one.

There was one consolation. If he got it wrong, he'd never know it.

Somehow the dragon was worse on the ground. In the air it was an elemental thing, graceful even when it was trying to burn you to your boots. On the ground it was just a damn great animal.

Its huge head reared against the grey of dawn, turning slowly.

Lady Ramkin and Vimes peered cautiously from behind a watertrough. Vimes had his hand clamped over Errol's muzzle. The little dragon was whimpering like a kicked puppy, and fighting to get away.

“It's a magnificent brute,” said Lady Ramkin, in what she probably thought was a whisper.

' 'I do wish you wouldn't keep saying that,'' said Vimes.

There was a scraping noise as the dragon dragged itself over the stones.

' 'I knew it wasn't killed,'' growled Vimes.' “There were no bits. It was too neat. It was sent somewhere by some sort of magic, I bet. Look at it. It's bloody impossible! It needs magic to keep it alive!”