'That's about enough, I think,' said Susan, stepping forward. The man was spun around. An elbow was jabbed into his stomach and then the palm of her hand caught him so hard under his chin that he was lifted off the floor and slammed against the wall. As he fell, Susan hit him on the head with a wrench. 'We might as well be going,' she said, as if she'd just shuffled some paper that had been untidy. 'Nothing more for us here.'

'You killed him!'

'Certainly. He's not a human being. I have... a sense about these things. It's sort of inherited. Besides, go and pick up the hose. Go on.' Since she was still holding the wrench, Lobsang did so. Or tried to do so. The coil she'd flung into the corner was knotted and tangled like rubber spaghetti. 'Malignancy, my grandfather calls it,' said Susan. 'The local hostility of things towards non- things always increases when there's an Auditor about. They can't help it. The hosepipe test is very reliable in the field, according to a rat I know.' Rat, thought Lobsang, but he said: 'What's an Auditor?'

'And they have no sense of colour. They don't understand it. Look how he's dressed. Grey suit, grey shirt, grey shoes, grey cravat, grey everything.'

'Er... er ... perhaps it was just someone trying to be very cool?'

'You think so? No loss there, then,' said Susan. 'Anyway, you're wrong. Watch.' The body was disintegrating. It was a fast and quite un-gory process, a sort of dry evaporation. It simply became floating dust, which expanded away and vanished. But the last few handfuls formed, just for a few seconds, a familiar shape. That too vanished, with the merest whisper of a scream. 'That was a dhlang!' he said. 'An evil spirit! The peasants down in the valleys hang up charms against them! But I thought they were just a superstition!'

'No, they're a substition,' said Susan. 'I mean they're real, but hardly anyone really believes in them. Mostly everyone believes in things that aren't real. Something very strange is going on. These things are all over the place, and they've got bodies. That's not right. We've got to find the person who built the clock-'

'And, er, what are you, Miss Susan?'

'Me? I'm... a schoolteacher.' She followed his gaze to the wrench that she still held in her hand, and shrugged. 'It can get pretty rough at break time, can it?' said Lobsang.

There was an overpowering smell of milk. Lu-Tze sat bolt upright. It was a large room, and he had been placed on a table in the middle of it. By the feel of the surface, it was sheeted with metal. There were churns stacked along the wall, and big metal bowls ranged beside a sink the size of a bath. Under the milk smell were many others - disinfectant, well-scrubbed wood and a distant odour of horses. Footsteps approached. Lu-Tze lay back hurriedly and shut his eyes. He heard someone enter the room. They were whistling under their breath, and they had to be a man, because no woman in Lu-Tze's long experience had ever whistled in that warbling, hissing way. The whistling approached the slab, stayed still for a moment, then turned away and headed for the sink. It was replaced by the sound of a pump handle being operated. Lu-Tze half opened one eye. The man standing at the sink was quite short, so that the standard-issue blue-and-white striped apron he wore almost reached the floor. He appeared to be washing bottles. Lu-Tze swung his legs off the slab, moving with a stealthiness that made the average ninja sound like a brass band, and let his sandals gently touch the floor. 'Feeling better?' said the man, without turning his head. 'Oh, er, yes. Fine,' said Lu-Tze. 'I thought, here's a little bald monk sort of a fellow,' said the man, holding a bottle up to the light to inspect it. 'With a wind-up thing on his back, and down on his luck. Fancy a cup of tea? Kettle's on. I've got yak butter.'

'Yak? Am I still in Ankh-Morpork?' Lu-Tze looked down at a rack of ladles beside him. The man still hadn't looked round. 'Hmm. Interestin' question,' said the bottle-washer. 'You could say you're sort of in Ankh- Morpork. No to yak milk? I can get cow's milk, or goat, sheep, camel, llama, horse, cat, dog, dolphin, whale or alligator if you prefer.'

'What? Alligators don't give milk!' said Lu-Tze, grasping the biggest ladle. It made no noise as it came off its hook. 'I didn't say it was easy.' The sweeper got a good grip. 'What is this place, friend?' he said. 'You are in... the dairy.'

The man at the sink said the last word as if it was as portentous as 'castle of dread', placed another bottle on the draining board, and, still with his back to Lu-Tze, held up a hand. All the fingers were folded except for the middle digit, which was extended. 'You know what this is, monk?' he said. 'It's not a friendly gesture, friend.' The ladle felt good and heavy. Lu-Tze had used much worse weapons than this. 'Oh, a superficial interpretation. You are an old man, monk. I can see the centuries on you. Tell me what this is, and know what I am.' The coldness in the dairy got a little colder. 'It's your middle finger,' said Lu-Tze. 'Pah!' said the man. 'Pah?'

'Yes, pah! You have a brain. Use it.'

'Look, it was good of you to-'

'You know the secret wisdoms that everyone seeks, monk.' The bottle-washer paused. 'No, I even suspect that you know the explicit wisdoms, the ones hidden in plain view, which practically no one looks for. Who am I?' Lu-Tze stared at the solitary finger. The walls of the dairy faded. The cold grew deeper. His mind raced, and the librarian of memory took over. This wasn't a normal place, that wasn't a normal man: A finger. One finger. One of the five digits on a- One of five. One of Five. Faint echoes of an ancient legend signalled his attention. One from five is four. And one left over. Lu-Tze very carefully hung the ladle back on its hook. 'One from Five,' he said. 'The Fifth of Four.'

'There we are. I could see you were educated.'

'You were... you were the one who left before they became famous?'

'Yes.'

'But... this is a dairy, and you're washing bottles!'

'Well? I had to do something with my time.'

'But... you were the Fifth Horseman of the Apocalypse!' said Lu-Tze. 'And I bet you can't remember my name.' Lu-Tze hesitated. 'No,' he said. 'I don't think I ever heard it.' The Fifth Horseman turned round. His eyes were black. Completely black. Shiny, and black, and without any whites at all. 'My name,' said the Fifth Horseman, 'is...'

'Yes?'

'My name is Ronnie.' Timelessness grew like ice. Waves froze on the sea. Birds were pinned to the air. The world went still. But not quiet. There was a sound like a finger running around the rim of a very large glass. 'Come on,' said Susan. 'Can't you hear it?' said Lobsang, stopping. 'But it's no use to us-' She pushed Lobsang back into the shadows. The robed grey shape of an Auditor appeared in the air halfway down the street, and began to spin. The air around it filled with dust, which became a whirling cylinder, which became, slightly unsteady on its feet, something that looked human. It rocked backwards and forwards for a moment. It raised its hands slowly and looked at them, turning them this way and that. Then it marched away, purposefully. Further along the street it was joined by another one, emerging from an alley. 'This really isn't like them,' said Susan, as the pair turned a corner. 'They're up to something. Let's follow them.'

'What about Lu-Tze?'

'What about him? How old did you say he was?'

'He says he's eight hundred years old.'

'Hard to kill, then. Ronnie's safe enough if you're alert and don't argue. Come on.'

She set off along the streets. The Auditors were joined by others, weaving between the silent carts and motionless people and along the street towards, as it turned out, Sator Square, one of the biggest open spaces in the city. It was market day. Silent, motionless figures thronged the stalls. But, amongst them, there were scurrying grey shapes. 'There's hundreds of them,' said Susan. 'All human-shaped, and it looks like they're having a meeting.' Mr White was losing patience. Until now he had never been aware that he had any, because if anything he had been all patience. But now he could feel it evaporating. It was a strange, hot sensation in his head. And how could a thought be hot? The mass of incarnated Auditors watched him nervously. 'I am Mr White!' he said, to the luckless new Auditor that had been brought before him, and shuddered with the astonishment of using that singular word and surviving. 'You cannot be Mr White also. It would be a matter of confusion.'

'But we are running out of colours,' said Mr Violet, intervening. 'That cannot be the case,' said Mr White. 'There is an infinite number of colours.'

'But there are not that many names,' said Miss Taupe. 'That is not possible. A colour must have a name.'

'We can find only one hundred and three names for green before the colour becomes noticeably either blue or yellow,' said Miss Crimson. 'But the shades are endless!'

'Nevertheless, the names are not.'

'This is a problem that must be solved. Add it to the list, Miss Brown. We must name every possible shade.' One of the female Auditors looked startled. 'I cannot remember all the things,' she said. 'Nor do I understand why you are giving orders.'

'Apart from the renegade, I have the greatest seniority as an incarnate.'

'Only by a matter of seconds,' said Miss Brown. 'That is immaterial. Seniority is seniority. This is a fact.' It was a fact. Auditors respected facts. And it was also a fact, Mr White knew, that there were now more than seven hundred Auditors walking rather awkwardly around the city.

Mr White had put a stop to the relentless increase in incarnations as more and more of his fellows rushed into the trouble spot. It was too dangerous. The renegade had demonstrated, he pointed out, that the human shape forced the mind to think in a certain troublesome way. The utmost caution was necessary. This was a fact. Only those with a proven ability to survive the process should be allowed to incarnate and complete the work. This was a fact. Auditors respected facts. At least until now. Miss Brown took a step back. 'Nevertheless,' she said, 'being here is dangerous. It is my view that we should discarnate.' Mr White found his body replying by itself. It let out a breath of air. 'And leave things unknown?' he said. 'Things that are unknown are dangerous. We are learning much.'

'What we are learning makes no sense,' said Miss Brown. 'The more we learn, the more sense it will make. There is nothing we cannot understand,' said Mr White. 'I do not understand why it is that I now perceive a desire to bring my hand in sharp contact with your face,' said Miss Brown. 'Exactly my point,' said Mr White. 'You do not understand it, and therefore it is dangerous. Perform the act, and we will know more.' She hit him. He raised his hand to his cheek. 'Unbidden thoughts of avoidance of repetition are engendered,' he said. 'Also heat. Remarkably, the body does indeed appear to do some thinking on its own behalf.'

'For my part,' said Miss Brown, 'the unbidden thoughts are of satisfaction coupled with apprehension.'

'Already we learn more about humans,' said Mr White. 'To what end?' said Miss Brown, whose sensations of apprehension were increasing at the sight of the contorted expression on Mr White's face. 'For our purposes, they are no longer a factor. Time has ended. They are fossils. The skin under one of your eyes is twitching.'

'You are guilty of inappropriate thought,' said Mr White. 'They exist. Therefore we must study them in every detail. I wish to try a further experiment. My eye is functioning perfectly.' He took an axe from a market stall. Miss Brown took another step back. 'Unbidden thoughts of apprehension increase markedly,' she said.

'Yet this is a mere lump of metal on a piece of wood,' said Mr White, hefting the axe. 'We, who have seen the hearts of stars. We, who have watched worlds burn. We, who have seen space tormented. What is there about this axe that could cause concern to us?' He swung. It was a clumsy blow and the human neck is a lot tougher than people believe, but Miss Brown's neck exploded into coloured motes and she collapsed. Mr White looked around at the nearest Auditors, who all stepped back. 'Is there anyone else who wishes to try the experiment?' he said. There was a chorus of hasty refusals. 'Good,' said Mr White. 'Already we are learning a great deal!'