The big chalkboard in Sister Merrow’s washroom had never been intended for town mapmaking, but by four o’clock that afternoon, there was no other surface in Lowbank large enough to hold the truth. Pella Rook stood before the slate, her right hand powdered white with pipe lime chalk. Meanwhile, Eren Tal held the heavy oak flat ruler against the wooden frame.
Pinned to the edges of the slate with iron tacks were two very different documents. On the left hung Eren’s grandfather’s linen-backed survey map of Lowbank. It was drawn in 1884 with faded sepia ink and showing the ancient town sewer vaults, canal water gates, and ferry slipways. On the right hung Tavi’s rough butcher’s parchment, its six penciled squares covered in beetle counts, heat readings, and street names scribbled in the boy’s awkward, childish hand.
Between the two maps, Pella was drawing the synthesis in three distinct colors: blue for Ada’s water pressure baselines, yellow for the load-bearing foundation piers, and red grease pencil for the insect congregation thickness.
The room was quiet except for the crackle of a small charcoal fire bowl Eren had brought in to dry the air and keep their fingers from going numb. The washroom smelled of boiled tea, dried elderberry ink. The ever-present damp silt stench that rose from the breached cellar wall behind them.
‘Read the numbers again, Tavi,’ Pella said, her eyes fixed on the intersection of Fish Street and Cooper Lane.
Tavi sat on the low woodbox. His bare feet was tucked under his wool smock, reading from his notes by the light of a lard lamp. ‘Old Mother Vane’s coal cellar: seventy-four beetles, mortar heat seventy-eight degrees. Cooperage dry store: eighty-one beetles, mortar eighty-two degrees. Red Anchor tavern: eighty-eight beetles, eighty-six degrees. Nine Lanterns boarding house: ninety-two beetles, ninety degrees flat.’
With each number, Pella pressed her chalk against the slate. She drew a series of nested curved lines streaming outward from the river wharf. At first, she had assumed the heat was a simple circular bleed, the way water ripples. Just then, a cobblestone is dropped into a horse trough. But as she connected the data points from the six basements, the shape refused to form a circle.
It was an ellipse—narrow, elongated, and sharp-nosed—pointing directly like an iron spearhead from the foundation vaults of the College of Summoners on the High Terrace, cutting straight down through the clay bluffs, and terminating beneath the Nine Lanterns boarding house.
Eren stepped back from the flat ruler, his heavy bushy eyebrows knitting together until they met over his crooked nose. He rubbed his stubbled chin with a calloused thumb, his breath misting faintly in the cold air. ‘That’s no natural slow leak, Pella. Slow leak follows the bedrock tilt toward the harbor boat ramp. That red line is cutting directly across the drainage contours.’
‘It’s not slow leak,’ Pella said. Her voice dropped into the quiet, hollow register that came over her whenever the shape of water resolved itself on paper. ‘Look at the centerline, Eren. Lay the flat ruler along the axis of the ellipse.’
Eren lifted the heavy ash rule, aligning its brass edge with the red chalk marks. The rule laid across the slate formed an exact fifty-two-degree slanted. He reached for a yellow grease pencil, tapped the town archives seal on his grandfather’s linen map. Then he traced a faint, dotted line engraved beneath the modern streets.
‘The High Pumping Gallery of 1842,’ Eren whispered, the wood of the ruler trembling slightly in his grip. ‘The abandoned diversion tunnel Hal Rook worked on when he was twenty years old.’
‘My father didn’t just work on it,’ Pella said. She stepped closer until her face was inches from the chalk. ‘He warned the city council forty years ago that if they ever high-pressure that gallery without venting the lower throat, the heat friction would shatter the shale layer beneath Lowbank. Look at what Sorell has done.’
Hal Rook’s original town survey notes had been dismissed by the High Council as the alarmism of an uncredentialed ferry mechanic. But her father had spent twelve winters recording the underground river currents with lead soundings and wax floats. He had known that the shale beneath Lowbank was not solid bedrock. But a layered sedimentary shelf interleaved with expanding blue clay.
She took a piece of blue chalk. Then she drew the internal intake pipe hub of the Hollow Crown as Ada had described it during her first sound survey. A massive, multi-tiered brass channel forcing five thousand gallons of river salt water per minute through a restricted four-foot baked-clay throat.
The blue intake lines were overlaid on top of the red beetle ellipse. Then, the match was exactly exact. The highest insect counts—ninety-two beetles per square foot at the Nine Lanterns—didn’t sit at the deepest point of Lowbank. They sat exactly where the drain tube’s high-pressure return pipe hub intersected the ancient, unmapped foundation piers of the old ferry end-post.
‘He isn’t just venting overflow down here,’ Pella said, turning to look at Eren. ‘The drain tube is cavitating so wildly upstream that Sorell can’t contain the backing-up pressure inside the college outer edge. If he vents it on the High Terraces, the marble fountains at the Great Sluice will erupt with boiling salt water. The town council will see the failure with their own eyes.’
‘So he’s dumping it on us,’ Eren growled. His hand closed into an iron fist against his apron. ‘He’s using the old ferry vaults as an unmetered spreading chamber. Lowbank becomes the radiator for his golden machine.’
‘It’s worse than that,’ Pella said, pointing the chalk at the outer boundary line. ‘Look at the spreading rate. Tavi’s counts from three days ago were thirty beetles per square foot at the bakery. Today it’s sixty-six. In seventy-two hours, the heat boundary has swelled forty yards outward.’
She tapped the slate with each word, leaving white chalk circles over the homes of their neighbors. ‘The drain tube isn’t just leaking, Eren. It’s expanding its catchment area into residential foundations. It’s baking the moisture out of the deep clay beds. When clay dries out under load, it shrinks. When it shrinks, the foundation footings drop.’
Tavi leaned forward from his woodbox, his face pale in the lamplight. ‘Does that mean the Nine Lanterns is going to fall down, Pella?’
‘Not today,’ Pella said, though her voice lacked conviction. ‘The timber frame has enough flex to absorb two or three inches of settlement. But the stone foundations won’t flex. They’ll shear along the mortar lines. A heavy spring tide hits that dried-out shale. Then, the river will blow the basement floors straight up into the parlors.’
The brass arch in the corner gave a faint, rhythmic pulse. Instead of a chime, a low ringing thrum that shook through the floorboards. The dial gauge mounted on the wall twitched its black pointer: forty-four PSI above datum. Two pounds higher than yesterday’s reading.
Sister Merrow pushed through the washroom curtain. She carried a tray with three steaming mugs of boiled tea and a plate of toasted sourdough crusts. She set the tray on the bench, looked at the slate covered in red ellipses and blue high-pressure vectors, and sighed. A long, weary sound that carried forty years of Lowbank endurance.
‘The landlord from the Nine Lanterns is at the front gate,’ Merrow said quietly. She wiped her hands on her apron. ‘Master Orv. He walked down through the slush with two of his rent-collectors. He says the hot water in his basement has reached his coal fire. His tenants are threatening to burn his carriage if he doesn’t bring a summoner to dry the floor.’
Eren picked up his mug of tea, blowing the steam across the dark surface. ‘Tell him to go to the High Terrace and hire a college wizard with a silk robe. See if Sorell will lift a finger for a Lowbank slumlord.’
‘No,’ Pella said, putting down her chalk and wiping her dusty hands on her tunic. ‘We don’t send him to Sorell. Sorell would send a cleansing squad to burn sulfur, kill the beetles, and seal the hatch with lead so no one can see the pressure gauge.’
She turned back to the map, tracing the red line that led straight to Master Orv’s cellar. ‘The Nine Lanterns sits directly on the main relief flap. If we can get inside that cellar legally, with a signed check contract, we can access the old ferry water chute without breaking town law.’
Eren set his tea down with a sharp clatter. ‘Orv won’t pay for a check, Pella. The man is a skinflint who charges widows for pump water.’
‘He’ll pay,’ Pella said, her voice hard and clear as river ice. ‘Because his coal is floating, his tenants are rioting, and we’re the only people in this city who know which pipe to turn. Tavi, put your boots on. Eren, get your pry bars. We’re going to give Master Orv an honest estimate.’