‘I’ll make sure it goes smoothly.’

She pulled her oversized cardigan closed and sipped her coffee. ‘This is the culmination of years of work since I unveiled the model. The dam has occupied my every waking hour…and my sleep too. But I doubt the reporters care. They look for other stupid stories and then concentrate on the wrong one. They’ll chase off after any scandal no matter how momentous the occasion.’

I said, ‘It’s all right. Don’t worry, just leave them to me. I’m used to keeping them in check. If they ask me a question I can’t answer, I’ll bring you in.’ I waved my hand in the air and Frost stared at it. I dug it into my pocket. ‘I’ll find a quick flight refreshing. The dam breaks up the air in interesting ways. It is a masterpiece.’

‘Oh, yes! It really is the most efficient structure! There’s never been a dam with the functional strength of this one, there’s never been a lake so capacious!’ Keen enthusiasm lit her face. She had been boring people on the subject of river engineering for three hundred and fifty years and this was her greatest project. ‘It makes Micawater Bridge look like an apprentice piece! Every engineer said I was being over-ambitious, but the figures were sound. So is the actualisation! They said it was impossible. They said, “You might hold the model in your hands but you’ll never raise the biggest construction of all time right on the Insects’ doorstep.” Three years later, I took them for a tour! Since the Wrought blast furnaces are operational again I’ve had iron for the rack and pinion cast in segments and assembled here, an elegant solution, you must admit, and you should look out for the way I’ve bridged the walkway above the overflow conduit so-’

‘Frost, please…’

‘I thought you liked it.’

‘I do, but you’ve just asked me to call in Lightning and Eleonora.’

‘Oh yes,’ she said, chastened. ‘So I did.’

I blew her a kiss with both hands that became a mock bow. ‘See you in an hour, OK?’

I walked out to the cobbled central courtyard, enclosed on its three other sides by the cookhouse, mess room and tavern. Each was built of limestone blocks and roofed with lauze; thick, heavy slabs that looked shaggy, like the boughs of a fir tree.

The buildings were pierced with arched alleys, three in each side, just wide enough for one man at a time. They were designed to stop all but the smallest Insects reaching this square, a final refuge if the town’s outer defences were ever penetrated.

The plain hall had fulfilled many purposes over the years: a hospital, a headquarters for immortals, and it was now Queen Eleonora Tanager’s temporary residence and Frost’s office. Frost’s orange banner ran along the length of the roof: ‘Riverworks Company Est. 1692’ in bold black letters. Beside it flew Tanager’s swan pennant, Micawater’s argent mascle on an azure field, and the Awian white eagle on sky blue.

Soldiers had gathered outside the Primrose Tavern opposite. They sat on stools made from barrels to watch two immortals sparring in the middle of the square. The Swordsman, Serein Wrenn, was fighting the Polearms Master, Lourie Hurricane. They had an Eszai competitive edge to their play; they both knew that if they weren’t training, somewhere a potential Challenger was.

Lourie Hurricane was a quiet perfectionist, a tall man from Plow who used to be a vavasour cart-driver before he became immortal. Serein Wrenn, on the other hand, was short and stocky and had the silliest haircut of all the Eszai-waxed up into short spikes with bleached tips. His narrow sideburns tapered into a little chinstrap beard.

Wrenn had come forward and beaten the previous Serein in a fair Challenge, according to the Castle’s rules, only five years ago. Many still said that his predecessor was the more steadfast fighter, but Wrenn was quick with the desperate gambit. He had frequently been Challenged until word of his flair spread. He had latched on to Lourie; I think he admired Lourie’s ascetic, taciturn poise. In the depths of his aplomb Lourie might have been grateful; it is always the case that Eszai lose friends but gain sparring partners. These two were often seen together arguing monomaniacally as to whether glaives or broadswords were the better weapons.

There were both objects of great amusement to the other immortals seated nearby watching them fight: Tornado the Strongman, the Sapper, the Artillerist, and Gayle Holthen the Castle’s Lawyer who also acted as provost for the fyrd. She was a smart, cosmopolitan woman who had joined the Circle after a full career as a judge.

Lourie swept his glaive in balletic circling moves, not one millimetre out of the perfect sequence. He dipped the two-metre pole, swept the pointed blade under Wrenn’s feet. Wrenn jumped it. Its hook caught behind his shin as he landed. Lourie tugged the pole with a grace that belied his strength. Wrenn hopped and let the hook slip out under his foot.

Gayle laughed and clapped her hands, bringing the Cook out of the tavern to watch.

All fifty immortals were arriving. I had been calling them up one by one, either from the Castle or wherever they’d been pursuing their interests elsewhere. Those involved in advance planning had been here for a month but all would be assembled by the end of the week.

Immortals, called Eszai in the low Awian language, are people proven to be the best in the world at their chosen profession. We all play our parts in the battle, because the Emperor San joins us to the Circle and shares his immortality with us as long as we lead the war. Here at the front we have overall authority, even over governors and the Queen; but elsewhere, or in issues not connected with the war we can do no more than advise them. Likewise, San’s word is advice to the world but to us it is law.

Wrenn deflected Lourie’s blade. Lourie pulled it back, grinding its rebated edge, and thrust the metal-clad base of the pole. Wrenn parried it with a full-strength clash. The mortals watching gasped, but we Eszai knew Lourie’s great skill; we’d seen it a hundred times before.

The Castle saves the very best and improves on it gradually, incrementally; little is ever lost. I’ve been Comet for two hundred years, the fastest Messenger of all time. I’m a freak, yes, but it means I get to live forever.

I turned to the wall behind me, took a grip on the rough stone and pulled myself up. I climbed swiftly past the doorway and the plaque above it; the only decoration in the town. Its sgraffito red plaster, incised through to the white layer underneath, depicted the Castle’s sun-in-splendour standard, surrounded by an inscription: ‘In memory of the battle at Slake crossroads, one night in the ongoing war. 4981 Plainslanders, Awians and Morenzians died on the l2th of April 1925.’

As if we need to be reminded, I thought as I pulled myself over the guttering and scrabbled up to the apex of the roof. Balancing there, I looked down on the mortal soldiers outside the pub and I suddenly realised they did need to be reminded. The massacre was three generations in the past, long out of their living memory. It meant nothing to them but a date in a schoolbook. I stepped lightly along the ridge, thinking for the first time that I had more in common with the other Eszai than with the mortals, the Zascai, who had no idea what it was like to stumble through the middle of a massacre. I contemplated with dread that no matter how much effort I put in to knowing every up-to-date trend in Zascai fashion and the developments in their business, the gap between us was steadily widening. Well, I decided, it isn’t inevitable that I will become as out of touch as Frost or Lightning. I must simply try harder; it’s my profession after all.

From the rooftop I saw the series of concentric squares in which the town was laid out. The buildings around the courtyard formed the first of three rings. Behind them ran a wide road, then another ring comprising the smithy, workshops, food, livery and ammunition stores, since Slake Cross is the supply base for all of western Lowespass. Every junction was staggered to prevent any Insects that might get in running straight to the heart of the town.