Any more of this and he’d end up like Groat, mad as a spoon. But there was more to this place. Somewhere there had to be a door—

His head was all over the wall…

Look, he said to his imagination, if this is how you’re going to behave, I shan’t bring you again.

But, with its usual treachery, it went on working. He’d never, ever, laid a finger on anyone. He’d always run rather than fight. And murder, now, surely murder was an absolute? You couldn’t commit 0.021 of a murder, could you? But Pump seemed to think you could murder with a ruler. Okay, perhaps somewhere downstream people were… inconvenienced by a crime, but… what about bankers, landlords, even barmen? ‘Here’s your double brandy, sir, and I’ve 0.0003 killed you’? Everything everyone did affected everyone, sooner or later.

Besides, a lot of his crimes weren’t even crimes. Take the ring trick, now. He never said it was a diamond ring. Besides, it was depressing how quickly honest citizens warmed to an opportunity to take advantage of a poor benighted traveller. It could ruin a man’s faith in human nature, if he had one. Besides…

The third floor yielded another avalanche of letters, but when they subsided there was still a wall of paper plugging the corridor beyond. One or two rustling envelopes fell out, threatening a further fall as Moist advanced.

In fact it was retreat that was at the top of his mind, but the stairs were now layered with sliding envelopes and this was not the time to learn dry-slope skiing.

Well, the fifth floor would have to be clear, wouldn’t it? How else could Sideburn have got to the stairs in order to meet his appointment with eternity? And, yes, there was still a piece of black and yellow rope on the fourth-floor landing, on a drift of letters. The Watch had been here. Nevertheless, Moist opened the door with care, as a watchman must have done.

One or two letters fell out, but the main slide had already taken place. A few feet beyond there was the familiar wall of letters, packed as tight as rock strata. A watchman had been in here, too. Someone had tried to break through the wordface, and Moist could see the hole. They’d put in their arm, full length, just as Moist was doing. Just like his, their fingertips had brushed against yet more compacted envelopes.

No one had got on to the stairs here. They would have had to walk through a wall of envelopes at least six feet thick…

There was one more flight. Moist climbed the stairs, cautiously, and was halfway up when he heard the slide begin, below him.

He must have disturbed the wall of letters on the floor below, somehow. It was emerging from the corridor with the unstoppability of a glacier. As the leading edge reached the stairwell, chunks of mail broke off and plunged into the depths. Far below, wood creaked and snapped. The stairway shivered.

Moist ran up the last few steps to the fifth floor, grabbed the door there, pulled it open and hung on as another mailslide poured past him. Everything was shaking now. There was a sudden crack as the rest of the staircase gave way and left Moist swinging from the handle, letters brushing past.

He swung there, eyes shut, until the noise and movement had more or less died away, although there was still the occasional creak from below.

The stairs had gone.

With great care, Moist brought his feet up until he could feel the edge of the new corridor. Without doing anything so provocative as breathing, he changed his grip on the door so that now he had hold of the handle on both sides. Slowly, he walked his heels through the drift of letters on the corridor floor, thus pulling the door closed, while at the same time getting both hands on to the inner handle.

Then he took a deep breath of the stale, dry air, scrabbled madly with his feet, bent his body like a hooked salmon and ended up with just enough of himself on the corridor floor to prevent a fall through sixty feet of letters and broken woodwork.

Barely thinking, he unhooked the lamp from the doorpost and turned to survey the task ahead.

The corridor was brightly lit, richly carpeted and completely free of mail. Moist stared.

There had been letters in there, wedged tight from floor to ceiling. He’d seen them, and felt them fall past him into the stairwell. They hadn’t been a hallucination; they’d been solid, musty, dusty and real. To believe anything else now would be madness.

He turned back to look at the wreckage of the stairs and saw no doorway, no stairs. The carpeted floor extended all the way to the far wall.

Moist realized that there had to be an explanation for this, but the only one he could think of now was: it’s strange. He reached down gingerly to touch the carpet where the stairwell should be, and felt a chill on his fingertips as they passed through it.

And he wondered: did one of the other new postmasters stand here, just where I am? And did he walk out over what looked like solid floor and end up rolling down five flights of pain?

Moist inched his way along the corridor in the opposite direction, and sound began to grow. It was vague and generalized, the noise of a big building hard at work, shouts, conversations, the rattle of machinery, the crowded susurrus of a thousand voices and wheels and footfalls and stampings and scribblings and slammings all woven together in a huge space to become the pure audible texture of commerce.

The corridor opened out ahead of him, where it met a T-junction. The noise was coming from the brightly lit space beyond. Moist walked towards the shining brass railing of the balcony ahead—

—and stopped.

All right, the brain has been carried all the way up here at great expense; now it’s time for it to do some work.

The hall of the Post Office was a dark cavern filled with mountains of mail. There were no balconies, no shining brasswork, no bustling staff and as sure as hell there were no customers.

The only time the Post Office could have looked like this was in the past, yes?

There was balconies, sir, all round the big hall on every floor, made of iron, like lace!

But they weren’t in the present, not in the here and now. But he wasn’t in the past, not exactly. His fingers had felt a stairwell when his eyes had seen carpeted floor.

Moist decided that he was standing in the here and now but seeing in the here and then. Of course, you’d have to be mad to believe it, but this was the Post Office.

Poor Mr Sideburn had stepped out on to a floor that wasn’t there any more.

Moist stopped before stepping out on to the balcony, reached down, and felt the chill on his fingertips once again as they went through the carpet. Who was it - oh, yes, Mr Mutable. He’d stood here, rushed to look down and—

—smack, sir, smack on to the marble.

Moist stood up carefully, steadied himself against the wall, and peered gingerly into the big hall.

Chandeliers hung from the ceiling, but they were unlit because sunlight was pouring through the sparkling dome on to a scene innocent of pigeon droppings but alive with people, scuttling across the chequerboard floor or hard at work behind the long polished counters made of rare wood, my dad said . Moist stood and stared.

It was a scene made up of a hundred purposeful activities that fused happily into a great anarchy. Below him big wire baskets on wheels were being manhandled across the floor, sacks of letters were being tipped on moving belts, clerks were feverishly filling the pigeon-holes. It was a machine, made of people, sir, you should’ve seen it !

Away to Moist’s left, at the far end of the hall, was a golden statue three or four times life size. It was of a slim young man, obviously a god, wearing nothing more than a hat with wings on, sandals with wings on and - Moist squinted - a fig leaf with wings on? He’d been caught by the sculptor as he was about to leap into the air, carrying an envelope and wearing an expression of noble purpose.