The water began to stick, splashes fattening on the glass.

Harry Hunt, Observator of the Royal Society of London for the Improving of Natural Knowledge, stopped to look more closely at the change in form, as rain turned to snow. Fingers stiffened by the chill, he wiped at his spectacles, and watched the first flakes settle on the brown leather of his coat.

He committed the observation to his memory and moved on. His purposeful stride took him past the new Bethlehem Hospital sprawling across Moorfields, smudges of light escaping its windows.

He had a slight frame and pale London skin.

South down Broad Street. The narrow buildings shouldered one another, pressing together for warmth. Untouched by the fury of the Great Conflagration, they followed the old scheme.

Harry made his way towards Gresham’s College, the mansion used by the Royal Society, to see the Curator of Experiments and Professor of Geometry there, Mr. Robert Hooke.

Falling thickly, the snow had already settled despite the wet ground. The early morning sky was violet, the colour of a bruise.

Harry’s steps echoed through the archway leading to the College quadrangle. In the stables, the horses snorted, and he heard the grate of their shoes. He turned for the south-east corner and stopped at a door.

Above him, a window clattered open and the head of a boy appeared.

‘Mr. Hunt! Mr. Hooke’s already gone!’

Harry put his finger to his lips. Tom Gyles, with a pantomime grimace, acted out his understanding.

Ah, discretion was required. No less loudly, he called down again.

‘I’ll come to you! Mr. Hooke would desire no stranger hear the business.’

Harry let himself in with his key and shook off the snow from his coat onto the lobby’s neat flagstones.

Perhaps a philosophical business engaged the Curator. The Royal Society kept him busy with his trials and demonstrations for the Fellows. Hooke also worked as Surveyor to the City of London, with Sir Christopher Wren. A far more lucrative employment, rebuilding the new London. Maybe he went to perform a view.

The rest of the boy belonging to the head arrived, zig-zagging down the stairs. A rope of hair stuck up from his crown, giving him the look of a shaggy sundial.

Harry looked past him, on the chance he might glimpse Hooke’s niece, Grace. At this hour, though, she would still be in her bed. A little wistfully, he returned his thoughts to Tom.

‘Mr. Hooke is gone to his new bridge at Holborn, to meet with Sir Edmund Bury Godfrey!’ Tom was hopping from foot to foot. ‘The messenger’s knocking woke us all.’So, Grace was awake …

Hooke had wanted help with his improved design for a lamp, its self-fuelling mechanism misbehaving.

‘I shall return later, then, when his business is done.’

‘He asks that you join them there.’ Tom looked slyly up at Harry, watching his eyes widen, pleased with the result of his information, happy he had held it back for most effect.

Harry felt a pulse of anxiety. Sir Edmund was renowned throughout London as a pervasive, threatening presence.

‘I shall go there. Oh, I forgot—a Happy New Year’s Day to you, Tom.’

‘And to you, Mr. Hunt. A happy 1678 for us all.’

Harry left the boy behind him and walked back across the quadrangle.

Grace watched him leave from her upstairs window, observing the trail of his boots as they dragged through the snow.

***

The smell of fish, flesh, and fruit from the Stocks. Breakfast.

By the statue overlooking the market—Charles II and his mount trampling Oliver Cromwell’s head—Harry bought a pastry and Dutch biscuits from a man half-asleep by his stall.

The pastry was too hot to eat, and too hot to hold. He swapped it from hand to hand as he walked. Up the gradual climb of Cheapside. Past where the Cross had stood until its destruction by Puritan enthusiasm. This had happened ten years before Harry was born, yet people still referred to it as a landmark—the more pious offered their thoughts on the Whore of Babylon as they did.

Friday Street, Gutter Lane, Foster Lane, and Old Change.

Here, all had burned in the Conflagration. In between these townhouses, warehouses, and shops—brick and stone, to the post-Fire regulations and standards—some spaces still remained. Sad patches of land, never reclaimed, their charred ruins dispersed over time, replaced by litter, nettles, and dirt.

Lines of stones reached up from the wharfs. The largest took days to be dragged from the quayside. The Cathedral awaited them, its ribs and stomach open to the sky. Surrounding it lay more stones, bricks, earth, and timbers. Like organs cut from it, more than materials to build it up.

From where the arch of Newgate used to be, before fire, too, destroyed it, Harry walked down the winding lane of Snow Hill, sliding, almost falling, and then to Holborn Hill.

Wiping the last pieces of pastry from his fingers, he transferred his attention to a biscuit.

He was at Holborn Bridge, spanning the Fleet River.

***

‘Hoy! Go no further!’

An old man in a coachman’s coat stepped out from the doorway of the Three Tuns, halting Harry with an unsteady palm. His face was a cracked glaze of lines under a worn-out montero. The wool of the hat was wet through, sagging over his shoulders. Despite his age, he was a hard-looking man, and far broader than Harry.

‘What happens here?’ Harry asked, in as business-like a tone as he could muster, wiping biscuit crumbs from his chin.

‘A finding—no mind of yours!’

‘If Sir Edmund Bury Godfrey’s done the finding, then I’m to meet him. Mr. Robert Hooke accompanies the Justice, does he not?’

The man, a constable of the watch, scowled at him.

‘I am Mr. Harry Hunt, Observator of the Royal Society, and assistant to Mr. Hooke,’ Harry added grandly.

With a cursory thumb, the constable sent him down to the river.

***

Robert Hooke had shaped this place, overseeing the Fleet’s straightening, deepening, and widening. It had taken four years of difficulty and disaster: the riverbed re-dredged after floods, the weight of the banks breaking the new timber wharfs, piles, and footings, the groundwater sweeping away the sluices and drains. The dumping of refuse from the abattoirs and households had continued, and rain washed in the wreckage left over from the Conflagration.

At last, it was finished. Vastly more expensive than the City had envisaged, the Fleet Canal was the biggest project of rebuilding the new London. All the way to the Thames was now smart with paved quaysides, and the watermen in their wherries could reach as far as the new Holborn Bridge.

Before, its main users had been floating dead dogs—their corpses bumping, sniffing one another in death as they had in life. Upstream, the Fleet continued as it always had: a silty, muddy-banked ditch. It disappeared into the hillside through an arch, a huge iron grating holding back the filth from Turnmill Brook.

Hooke sheltered beneath the span of the bridge. Harry easily recognised his hunched form, the twist in Hooke’s back diminishing what would have been a tall stature. Without the cover of a wig, his hair hung over his large forehead and stuck to his sharp chin, and his long nose, its nostrils red-rimmed, had a dewdrop hanging from its tip. He wore his favourite overcoat, a natural grey colour.

His protuberant silver eyes acknowledged the younger man’s arrival, but he said nothing to him.

Next to him, contrastingly upright, stood a tall, impressive man in a long black camlet coat, black leather gloves, and a large black hat. A sword, sheathed in a black scabbard, poked out behind him. His peruke, also black, swept around his large head and down over his shoulders. A single touch of ostentation: a band of gold fabric encircling the hat lessened his Puritan severity.

Sir Edmund resembled, Harry thought, a large inquisitive raven.

Harry jumped down from the quayside’s low wall, slipping on the bank. The Fleet slid viscously over the mud, eroding the snow to a clean, frosty edge.

Hooke merely pointed, directing Harry under the bridge. Northwards, away from the new wharfs of the Canal. Along the old, untouched muddy bank.

Harry walked past the two men, through the shadow of the arch, and back into the brightness of the falling snow.