The smell of hot iron rose from the blacksmith’s shop, mingling with the yellow-hay stink of horse turds on the road and the washy smell of potatoes boiling in the cookhouse adjoining the hall.

Below, the innkeeper thwacked a brass tap with a mallet to drive it into an enormous keg of beer. His blows rang around the square together with the wail of the innkeeper’s squab and its mother shushing as she tried to calm it. She held it inside her cream shawl, against her breasts. It flailed one naked pinion with three pointed fingers like the wing of a plucked chicken. ‘Squab’ is Morenzian slang for Awian babies before they are fledged, and it was probably crying from the itching as its pinfeathers were starting to push through.

The long buildings of the third ring were barracks to billet ten thousand troops. I could see the stone cisterns on the shower blocks’ roofs, replenished by recent rainstorms. The Awian soldiers had added a sauna and a talcum bath: conditions are bad enough at the front without suffering from lice in your wings.

Then came the stables and allotments, in shadow at the foot of the curtain wall. Mangy apple and hazelnut trees bowed over cramped, tilled plots with green shoots-hardy runner beans and turnips. The soldiers supplemented their diet by growing vegetables but they were only permitted to do so inside the walls because any kind of plant attracts Insects.

A few metal cages beside them each contained an Insect the size of a warhorse. Their jaws and antennae were bound with wire; they were soon to be sold and carted south to the Rachiswater amphitheatre. Their scent set mastiffs barking on the far side of town.

Towers reinforced the exterior curtain wall at intervals along its length and at all four corners. It was tall, height being more important against the Insects than thickness, and it extended below ground to stop them undermining it. Roofed wooden walkways overhung the tops of the walls along their lengths. The single gate faced north towards the Paperlands. A guard with a jaunty crest on her helmet stared out of the large, square windows in the gatehouse tower.

These military towns-Slake Cross, Frass and Whittorn-had been designed by Frost soon after her initiation to the Circle. She became a great favourite with the troops who no longer had to construct open air camps. Each town was in essence a fort, with a shifting population of fyrd and the people who supply them: quartermasters, fletchers, sutlers and male and female prostitutes.

Slake Cross gave me a sinking feeling like the cold trepidation you feel on returning to a place you knew long ago. All your friends have moved on; their houses have strangers in them now. Even the routes you used to walk have changed, because the pubs you knew have been boarded up and cafés opened where they shouldn’t be. The last time I was here I was completely screwed up, living on drug time, time measured by needles and veins, not real time at all, and I scarcely noticed how bleak and utilitarian the place was.

I concentrated on the far end of the roof, breathing calmly like a gymnast on the high bar, arms out for balance. I started running, opened my wings and their fingers spread automatically. They dragged, pulling me back, and I pushed at the tiles to find more speed. I lengthened my stride, faster still. I reached the end of the roof, sprang into the air, pulled my legs up and swept my wings down powerfully.

When I begin to fall I always-because I have the same instinct as everyone-expect to hit the ground immediately as if I’ve merely tripped. But I keep falling, feeling nothing under my feet but more thin air.

Two more desperate beats, and I strained my body upwards in a graceful curve. My wingtips came together in front of my face, then I pushed away and I was no longer falling. I stretched out my legs, lying horizontally.

The people below saw the soft inside surface of my black sickle wings, the sun shining through their trailing edges. I felt air spilling off every flight feather. Their hard and sharp leading edges rasped louder as I beat harder and gained height. I scraped over the tavern’s ridge, pushed off with my palms and started laughing ecstatically as I flapped over the road, the barrack ring, the curtain wall and out of town.

The Lowespass Road ran straight as a rule. Its cobbled, slightly convex surface was crispy with hoof prints in reddish clay mud. Water filled its drains; since the completion of the dam the whole countryside was like a puddle and pools had begun to appear all over the place.

From the air, Slake Cross looked like a square grey archery target lying on the contours of the pale green valley side. I looked back to the gatehouse. The gate, twice my height, was crisscrossed with deep iron strips. Shallow troughs scarred between them where Insect mandibles had reached through to scrape the old timber. On my right stretched the Lowespass Road and ahead the reservoir glimmered, flat and silver. I was heading towards the Insects’ Paperlands covering the entire north bank of the river and as far as I could see into the distance, like a white sheet drawn over the land.

Strong gusts kept me flying low, no more than twenty metres from the ground where I could follow a direct path with the minimum effort. I flew over the crossroads with the smaller Glean Road along which troops arrive from western Awia. The Slake Cross monument, a smooth obelisk, stood there on grass scattered with yellow primroses-fragile blooms transplanted from the river bank before the flooding process began. Ointment made from them is a sovereign salve for wounds, and they had become a symbol of the massacre.

The uncompromising hills were always striding along the horizon, their stony summits rose to mid-sky and framed Lowespass valley. Further east at Miroir there were exposed tracts of moorland covered in peat bogs. Pondskaters V-rippled over black gullies of acidic stagnant water and mosquitoes whined over patches of spongy sphagnum moss among the heather. At this end of the valley the soil was thin. Thistles and ragwort sprouted in the clints and grikes of the limestone pavements. Caves riddled the valley floor. For thousands of years the rainwater has been carving faults in the rock into fathomless potholes and massive chambers, where drops precipitate strange and magnificent formations like the Throne Room columns. The Insects’ own tunnels join the system; it does no good to think about it.

Slake Cross town itself is built over a resurgence of an underground stream, so it never lacks fresh water. Frost has used dye to investigate the routes of the system. She started messing about with the water table and everyone watched, unnerved, as the level in the deep well rose to its very brim.

The road crossed uneven ground, slicing through the outcrops, and a larger quarry had scarred the side of a big knoll. I glided over its levelled area where carts were parked, completely covered with hardened white lime dust.

I passed some lime kilns in the side of a cutting; room-sized stone ovens with ragged chimneys, now cold and empty, with charcoal heaps growing damp outside their mouths. Frost had constructed them and employed the stokers; as soon as she knew she had enough cement she had moved them to work on the dam itself. A high wall protected a stand of pine trees, which grew relatively quickly and Frost used for building material.

On the north side of the road was the first of a series of static catapults called petraries, set into a concrete platform slick with pools of green algae. Its waxed wooden beam and sturdy foundations glistened, beaded with rain water. Its cable had been removed and the counterweight box was empty. Barbed wire rolls stacked haphazardly beside its pyramid of ammunition stones. Far off I could just see the nearest peel tower, a link in the chain stretching from Frass to Summerday to monitor Insect activity.