He followed Mr Gunson into his office in the Division Street building, nodding to the clerk and rolling his shoulders. A thousand insects swarmed up and down his back. Mrs Gunson had warned him about this peculiar sensation. She had told him the intolerable itching was part of the healing process.

His boss set about unfolding a sheet of paper covered in straight and right-angled lines and shaded curves. He clipped it to the drawing board that dominated the room and gestured to Silas to take a closer look.

‘The front elevation of the embankment at Agden. I’m going to increase the size of the by-wash, here, on the right, do you see?’

Silas nodded. He was struggling to relate the clean, sharp lines of the drawing to the muddy site he was working on.

‘And it’s stepped, not sloped.’ Mr Gunson ran his finger over the elevation. ‘The outlet pipes, here and here… and the puddle wall…’

Silas had been taught how to manipulate wet clay to form a watertight seal between the embankment and the reservoir, and learned the method was an old one, adopted from canal building, but vastly scaled up. He knew now that the puddle wall had been a bone of contention in the investigation into the collapse of Dale Dyke. The outlet pipes, too.

Gunson’s voice washed over him. ‘…the basin will hold five hundred and fifty-nine gallons of water and covers twenty-five hectares. The material we excavate goes here, into the embankment, nothing is wasted… one hundred feet high and eleven hundred feet wide… aesthetics are important. The slope is sewn with grass and becomes part of the natural landscape…’

Silas’s eyes slid to the daguerreotype that was pinned to the wall next to the easel. It was a blurry black and white image of part of the valley, photographed in the immediate aftermath of the flood. The Loxley was a muddy swamp, its meandering banks a jumble of rubble and uprooted trees. A group of people posed in the foreground, tiny grainy figures on the edge of the scene. An old woman in a bonnet and apron over her long skirts, a younger woman standing slightly apart and clutching the hand of a small boy in a cap and four older bare-headed children holding each other’s hands like paper cut-out dolls. When Silas had first examined the daguerreotype, Mr Gunson confirmed it had been made the morning after the flood. He didn’t explain why he had it on the wall and Silas didn’t ask.

Gunson clapped his hands together.

‘We’re moving forward at a fair lick, eh, Silas? There’ll be a new Dale Dyke to follow Agden.’ He glanced up from his drawings and Silas saw that the skin around the older man’s deep-set eyes was smudged by fatigue. ‘I’ve been preoccupied and I’m afraid Mrs Gunson will be displeased with me this evening.’ He was holding a brass compass, absently pressing one of its two miniature spears against the soft pad of his thumb. ‘The nights are drawing in again. Have you noticed? And I shall have to work late once more.’