The six-foot slate chalkboard on the washroom wall had been wiped clean with vinegar. But the faint gray ghosts of yesterday’s gauge readings still clung to the slate pores like frost on winter slate. Imran Bell stood before it. He held a tin box of grease pencils and a three-foot wooden ruler that Eren Tal had planed down to a true edge.
Beside him on the drafting bench, a pot of boiled tea was steaming gently in the cold river draft, its bitter aroma mixing with the smell of wet stonework and pipe lime dust. Pella Rook sat on a high stool, her drafting compass open to two inches. Meanwhile, Eren leaned against the door post, his arms folded across his leather apron.
On the far corner of the workbench, Sister Merrow’s sourdough crust from the early bake sat cooling on a clean cotton cloth, its yeasty fragrance cutting through the chalky tang of the room. Outside, the morning tide was receding, leaving the usual silt stench clinging to the timber boat ramp.
‘In pest control,’ Imran began. He tapped the rule against the lower left corner of the slate, ‘you never look at where the insects are standing. You look at where they’re walking away from. An insect is a living vector. Every footstep it takes is a direct response to a physical pressure slope.’
He reached into the tin box and selected a yellow grease pencil. With quick, sure strokes, he passed the map points from Tavi’s pasteboard collection slips onto Eren’s street map. At each intersection—the brewery corner, the cooperage alley, the coal docks, the ferry larder—he drew a cluster of small yellow arrows indicating the direction the nurse beetles had been traveling when intercepted.
Eren leaned closer, squinting at the yellow marks in the lantern light. ‘Every single arrow on Fish Street points southwest. Downhill toward the mudflats.’
‘Not just downhill,’ Imran corrected. He drew a series of curved green lines connecting the arrow tails. ‘They’re moving straight-across to an advancing heat front. When I connect the points where the mortar heat registered above forty degrees, look at the shape.’
The green line didn’t follow the street contours, nor did it trace the natural gravel channels of the old riverbed. It curved in a clear, exactly precise arc. A segment of a huge circle whose outer edge stretched from the timber basin to the eastern canal lock.
Pella stood up from her stool, her eyes fixed on the curve. She picked up her brass divider and measured the distance from the outer arc to the inner ring of forty-eight-degree readings Imran had taken in the deep larder breach.
‘The radius is widening,’ Pella said, her voice dropping into a hard, focused whisper. ‘The rings are nested.’
Imran picked up a red grease pencil. ‘Give me the center point, Pella. Project the normals from those three arc segments.’
Pella placed the point of her steel scribe on the slate, aligning it along the bisectors of Imran’s arc. She drew three straight lines inward toward the upper right corner of the board. The three lines came together at a single, unavoidable intersection.
The chalk snapped in her fingers. The intersection lay directly beneath the massive, gold-trimmed towers of the College of Summoners on the High Terrace.
‘There’s your heat source,’ Imran said. He tapped the red intersection with the blunt end of his rule. ‘It’s not an accidental sewer leak, and it’s not natural river earth-heat activity. It’s an engineered heat epicenter. Something up there is generating millions of BTUs of waste heat and dumping it directly into the sub-terrace foundation gravels.’
Eren let out a long, low whistle through his teeth. ‘The High Terrace. Sorell’s master chamber. That’s where they’re building the core pipe hub for the Hollow Crown.’
‘And because the High Terrace sits on solid dark rock,’ Pella added, tracing the dropping lines of height, ‘the heat can’t fade downward into deep bedrock. The dark rock shelf acts like the bottom of an iron frying pan. The white-hot water and high-pressure steam are forced outward and downward, bleeding into the soft sedimentary gravels and ancient brick channels of Lowbank.’
Imran wiped his grease pencil on a rag, stepping back to view the completed diagram. ‘In Leeds, when a commercial laundromat dumped boiling boiler drain water into an unvented brick sewer in ninety-four, the expanding steam pushed three thousand sewer rats into the high street shops in twelve hours. The council blamed the restaurants for poor hygiene. Two months later, the main street collapsed into an empty cave because the mortar had washed away.’
He tapped the outer ring on the slate. ‘You have about three weeks before the heat envelope reaches fifty-five degrees at the riverfront. When it hits fifty-five, the mortar in these quayside foundations will begin to hydrolyze. The lime will turn back into chalk paste. The weight of the High Terrace will push the lower wards straight into the mud.’
Sister Merrow came to the washroom doorway, wiping her hands on a dry towel. She looked at the red circle on the slate, her weathered face grim in the blue glow of the Courtesy Bridge. ‘The College masters think they’re building an engine to control the river. But they’re just cooking their own foundation.’
‘They don’t know it’s happening,’ Pella said. That turned to look through the small window toward the glittering white marble of the upper city. ‘On the High Terrace, their floors are laid on marble slabs four feet thick. Their fountains run with ice water brought down from the mountains. They won’t feel the heat until the boat ramp buckles under their carriages.’
Eren picked up a dark oak-ink pen and a sheet of heavy rag thick parchment, preparing to copy Imran’s heat map down to the last tiny fraction of an inch. ‘We keep this board locked, Pella. If Corvin or his beadles see this drawing, they’ll declare it treason before they admit it’s plumbing.’
He uncapped his ink bottle and dipped a fresh goose quill. He laid out the grid map points with practiced wheelwright accuracy. ‘Every line on this thick parchment has to match the city survey pins Hal Rook drove thirty years ago. If we show this to the wardens, they’ll check the corner benchmarks first.’
Imran leaned over Eren’s shoulder, verifying the heat isotherms. ‘Mark the thirty-four-degree boundary with a dotted trace. That’s the threshold where the river beetles begin packing their brood capsules. If that line moves fifty yards west by next Tuesday, it means Sorell has brought the backup steam turbine online.’
Pella watched the dark ink sink into the fibers of the thick parchment. ‘When my father drew the original intake maps, he left three open spreading joints in the lower gallery specifically to relieve heat buildup. The College cemented those joints shut twelve years ago to stop unlicensed dock boys from catching eels in the water chutes.’
‘Cementing a spreading joint on a high-pressure line,’ Imran remarked. It shook his head, ‘is like welding the safety valve shut on a steam traction engine so you don’t hear the whistling. It makes the yard quiet right up until the boiler takes the roof off.’
He tapped his finger against the wooden ruler. ‘In West Yorkshire, when the colliery owners sealed the air-flow shafts to save on pump upkeep, the gas piled up in the crawlways until a single spark blew the headgear three hundred feet into the air. Water under steam pressure is no different than gas. It doesn’t forgive bad math.’
Sister Merrow poured fresh boiled tea into their mugs, her voice low and steady. ‘Hal Rook warned the judges thirty years ago that the river wasn’t a servant to be locked in a coal cellar. He told them the confluence had three lungs, and if they choked the middle lung, the river would drown the city in its sleep.’
‘Let them declare it whatever they like,’ Imran finished. They set his tools back into his canvas bag with deliberate care. ‘Physics doesn’t care about summoners’ robes. When steam expands, it pushes until something gives way. And right now, the only thing standing between this harbor and a foundation collapse is three dozen clay pot pots and a carpenter who knows how to brace a ceiling.’
The washroom arch gave a low, ringing chime, its runic indices shifting smoothly as Ada’s scheduled afternoon tracking data check began on the remote display.
Pella looked from the red epicenter on the slate to the cool, steady blue light of the Courtesy Bridge. ‘Hal Rook built this arch to measure what the College refused to see. We have the data, Eren. Now we have to make the city look at the board.’