“Morning, sir,” croaked the old man as he reached the entrance.

“Good morning to you,” came the reply from the man behind the desk.

The office was small and square, with narrow windows of smoked glass that looked out over Griss Fell and the arches of the Sud Line railway. One wall was flush with the looming dark bulk of Parliament’s main edifice. Set into that wall was a small sliding door. A pile of crates teetered in the corner.

The little room was one of the chambers that jutted from the main building, high over the surrounding city. The waters of the Gross Tar surged fifty feet below.

The delivery man unloaded his trolley of parcels and boxes in front of the pale middle-aged gentleman sitting before him.

“Not too many today, sir,” he murmured, rubbing his moaning bones. He went slowly back the way he came, his trolley jouncing lightly behind him.

The clerk sifted through the bundles and rattled out brief notes on his typewriter. He made entries in an enormous ledger labelled “ACQUISITIONS,” skimming the pages between sections and recording the date before each item. He opened up the packages and recorded the contents in a typewritten day-list and in the big book.

Militia reports: 17. Human knuckles: 3. Heliotypes (incriminating): 5.

He checked for which department each collection of items was bound, and he separated them into piles. When one pile had grown big enough, he put it in a crate and carried it over to the door in the wall. It was a four-by-four-foot square, which hissed with a rush of siphoned air and opened at the behest of some hidden piston when he tugged a lever. At its side was a little slot for a programme card.

Beyond it a wire cage dangled beneath Parliament’s obsidian skin, with one open side flush with the doorway. It was suspended above and on either side by chains that swung gently, rattled and disappeared into an eddying darkness that loomed off without remission in all directions that the clerk could see. The clerk lugged the crate up into the passageway and slid it along into the cage, which pitched a little under the weight.

He released a hatch which closed sharply, enclosing the crate and its contents with woven wire on all sides. Then he closed the sliding door, reached into his pocket and pulled out the thick programme cards he carried, each clearly marked: Militia; Intelligence; Exchequer; and so on. He slid the relevant card into the slot beside the door.

There would be a whirr. Tiny, sensitive pistons reacted to the pressure. Powered by steam driven up from the vast basement boilers, gentle little cogs rotated the length of the card. Where their spring-loaded teeth found sections cut from the thick board, they slotted neatly inside for a moment, and a minuscule switch was thrown further along the mechanism. When the wheels had completed their brief passage, the combination of on-off switches translated into binary instructions that raced in flows of steam and current along tubes and cables to hidden analytical engines.