It is a little-known fact that Ankh-Morpork has two taxation offices, in the same way that a conjuring trick has two halves: the one you are invited to watch, and the one where the actual work happens.

The Guild of Assessors was the half you watched. The other half was the Office of the Collector-General, which was the department of the city government legally responsible for receiving the money the Guild collected, and which had therefore had, for the better part of a century, nothing whatsoever to do.

It occupied a narrow building off Pseudopolis Yard with a sagging roofline and a brass plate so tarnished it now read OFF CE OF THE C LLECTOR-GE ERAL, which sounded like someone being strangled by bureaucracy and was, Moist felt, truth in advertising. Vetinari had given him the keys with the expression of a man giving someone a kitten he has reasons to want out of the palace.

Moist let himself in on a Tuesday morning, and stood in the hallway, and listened.

The Post Office, when he'd first entered it, had been full of the whispering of dead letters. The bank had hummed with the Glooper. This building had a different sound, and it took him a moment to identify it, because it was the sound of someone working — the steady scratch of a pen, far upstairs, going at a pace that suggested it had been going for a very long time and saw no reason to stop now.

He followed it up four flights, past offices full of dust sheets, to a door under the roof, and opened it onto the second-most extraordinary room he had ever seen.1

Every wall was shelved, and every shelf was full of ledgers — not the fat brown Guild kind, but slim ones, bound in cheap blue board, thousands of them, each spine numbered in a tiny, fierce, immaculate hand. At a desk by the window, writing in the newest one, sat a small elderly man in a clerk's coat that had been carefully mended so many times it was now mostly mends, with a cuff-guard on each sleeve and a pen behind each ear and a third pen in his hand, working.

'Office hours commence at eight,' said the old man, without looking up. 'It is now seven fifty-one. You may wait on the landing.'

'I'm Moist von Lipwig,' said Moist. 'The new Collector-General.'

'Then you may wait on the landing politely,' said the old man, and finished his line, and ruled it off, and blotted it, and only then looked up. He had the bright, suspicious eyes of a robin that has been promised crumbs before. 'Lipwig,' he said. 'The stamps man. Hmf. They do say you'll be dead by Hogswatch.'

'Who says?'

'Everyone in the trade. There's a book running. Mr Cripslock at the engravers has you at nine to two.' The old man stood, with a creak that out-creaked Slope's, and extended an ink-stained hand. 'Sideways. Junior Probationary Clerk, Second Class.'

'How long have you been the Junior Probationary Clerk, Second Class?'

'Fifty-three years come Sektober,' said Sideways, with grim pride. 'They stopped the promotions in '73, same year they stopped sending the work. The Guild does the assessing, see, and the Guild does the collecting, and the Guild sends the Treasury its figure once a year on a slip of paper, and this office's job is to receive that slip of paper. Two minutes' work, per annum. The rest of the staff drifted off over the decades. Died, retired, went mad, one of them ran away to sea, which takes doing in a city with the Ankh in it.'

'But you stayed,' said Moist, looking at the shelves. At the thousands of slim blue spines. At fifty-three years of the steady scratch of a pen with nothing official to write. 'Mr Sideways,' he said carefully, the way a man speaks when he can feel the floor of the universe tilting toward something, 'what's in the ledgers?'

Sideways drew himself up to his full five foot two.

'The job,' he said. 'Someone had to do the job, sir. The Guild sends one figure a year, but figures come from somewhere, don't they? So I kept my own books. I read the Gazette — the property sales, the ship arrivals, the Guild notices, the society pages, who built what and who married whom and who died worth how much. I walk the city on my half-day and I count windows. Forty years ago I started paying the street children a penny a week to tell me what gets unloaded at the docks of a night-time, and a penny goes a long way among the right class of urchin, sir, and further among their grandchildren, which is who reports to me now.'2 He gestured at the walls, with their fifty-three years of patient blue spines, and said, in the voice of a craftsman unveiling his life's work to the first person who had ever climbed the stairs to see it:

'That is what the city is actually worth, sir. Every street of it. And down in the cellar, cross-indexed, is what the Guild says it's worth, copied annual from their public filings. And the space between them two sets of books, sir,' and here the robin's eyes gleamed like a bird that has finally, after half a century, been shown the crumbs, 'the space between them is the deepest hole ever dug in this city, and Mr Albright Slope has been living down it since before you were born.'

There was a long silence, broken only by the sound of Moist von Lipwig falling in love.3

'Mr Sideways,' he said at last, 'how would you feel about a promotion?'

'Couldn't say, sir,' said Sideways. 'Never had one. I'd want to read the relevant regulations first.'

'You wrote the relevant regulations, didn't you?'

'In '81, sir, yes. Nobody else was using the office.'

In the Oblong Office, the grey gentleman sat in the visitor's chair without quite touching it, in the way that a reflection sits in a mirror.

It had been three minutes since he had spoken, and Lord Vetinari, who had stared down werewolf assassins, dragon-rampant mobs, and the combined heads of every Guild in the city, was finding the experience of being looked at by the Bureau of Universal Compliance genuinely novel. It was not like being watched by an enemy. Enemies wanted something. This was like being watched by a form — by something that had a box with his name on it, and was waiting, with no impatience whatsoever, for the box to be filled in.

'Let me see if I have understood you,' said Vetinari. 'You wish to inspect the city's accounts.'

The grey gentleman's mouth opened, and a half-second later, words came out of it. 'All accounts are subject to inspection. This has always been true. You are merely the first to be informed.'

'On whose authority?'

'On the authority of the rules.'

'Whose rules?'

'The rules,' said the grey gentleman, 'do not belong to anyone. That is what makes them rules. Things that belong to someone are called property, and property is an irregularity we shall be addressing in due course.' He produced, from no detectable pocket, a single sheet of grey paper, and laid it on the desk with a sound like a snowflake landing on a coffin. 'This is a Notice of Commencement. The audit of the entity designated ANKH-MORPORK begins at the beginning, proceeds through the middle, and concludes at the conclusion. You need do nothing. Doing nothing,' he added, 'is, we find, the activity at which your species shows the most promise, and we wish to encourage it.'

'And if the city declines to be audited?'

The grey gentleman tilted his head. The movement happened all at once, with no travel in between, like a clock hand jumping.

'Declines,' he said, as though tasting the word and finding it had no nutritional content. 'The avalanche does not accept the mountain's declination. We are not asking, your lordship. We are notifying. There is a difference, and the difference is the whole of our authority.' He rose, in the same all-at-once way. 'You will find us very fair. Everything that is in order will be confirmed. Everything that is not in order will be corrected. And when we reach the bottom of the file, we will assess the city's foundational exemption — the one all its accounts are built upon, the one for which no permit has ever been issued.'

'Which is?' said Vetinari, though something old and cold in the back of his mind, some inheritance from the first ancestor ever to watch the grey come down over the mountains, already knew.

The grey gentleman paused at the door, which did not open for him so much as stop being relevant.

'You are all,' he said, 'operating alive without a licence.'

And then there was no one in the room but Vetinari, and a sheet of grey paper on the desk, and the fire, which had gone out without smoke, all at once, as though it had been filed.

Vetinari sat motionless for some time. Then he reached for pen and paper, and began, in his small precise hand, a letter:

My dear Mister Lipwig. As you know, I never interfere in the departments I have delegated. You will therefore understand the gravity of what follows...