The ladder didn’t touch the stone wall for the first fifteen feet. It hung from the iron hatch ring by two forged hooks, swaying with a slow, swinging weight swing that made the wet hemp cords squeak like wet leather. Pella went down first. Her cart driver boots tested each ash rung before letting her full weight leave the upper timber. The heat rose to meet her like an open oven door in midsummer. It was thick, wet, and smelling of ancient river slime and scalded rock. Below her, the beam of her zinc lantern picked out the curved ribs of the gallery vault, where green moss had died. Then it turned to a black, slippery grease under the sudden blast of heat.
Her boot heel struck solid stone with a dull splash. She stood in three inches of lukewarm, silt-choked water that swirled around the ankles of her boots. She right away held her lantern high, scanning the dark hall. The Gallery of the Three Oars had been carved during the early ferry charters two hundred years ago. A high, vaulted tunnel eight feet wide, its walls built of dense red colonial brick joined with lime mortar. Every twenty yards, an arched niche was cut into the brickwork, each bearing the faded carved sigil of three crossed oars, the ancient mark of the Lowbank Watermen’s Guild.
Above her, the ladder groaned as Eren dropped, his heavy frame moving with deliberate, measured caution. He dropped into the water beside her with a heavy splash, his iron pry-bar clattering softly against his belt hook. Sister Merrow followed last. She used a canvas sling looped over the ladder stringers to ease the strain on her scarred knee. When her feet reached the water, she let out a sharp, gravelly breath, her nostrils flaring against the vapor.
‘Air is breathable,’ Merrow noted, holding up an animal fat rushlight. The flame stood steady, three inches tall, burning with a clear, yellow spear. ‘A bit heavy on the sulfur, but no coal gas yet. Keep your heads below the arch crown. The steam collects in the brick curve.’
They moved forward along the gallery floor. They stepped over broken pottery tiles, discarded iron hoops from long-rotted animal fat barrels, and deep deposits of black river mud. The water was flowing south, moving with a steady, sluggish draw toward the old harbor outlet. But along the ceiling, thick droplets of condensed steam rained down continuously. It was warm, oily drops that hissed faintly as they struck the hot glass of their lantern globes.
Pella paused at the third vault arch. She pulled her grease pencil from her apron pocket and stepped toward the massive timber shores that braced the tunnel roof. These were twelve-inch squared heartwood oak balks, blackened with creosote, wedged tight between stone wall-brackets and granite floor pads. Carved deep into the center of the largest timber was a clear, familiar mark. A stylized rook bird perched on an iron wrench, with the date Year -14 chiseled beneath it.
‘My father’s work,’ Pella said softly, her fingers tracing the rough edge of the oak.
Eren stepped up beside her, raising his lantern to the joint where the timber balk met the ceiling collar. He let out a low, flat whistle. ‘Your father knew how to square an oak, Pella. But look at the crown of that post. That timber was straight as a weighted drop-line when he drove the wedges.’
Pella looked up. The twelve-inch heartwood beam was bowed outward by nearly three inches at its center, the wood grain groaning under a huge, unnatural bending. Along the tension face of the oak, long stringy splinters had begun to lift, their edges white and frayed like broken hemp rope. The oak was weeping drops of hot sap that smelled like burnt vinegar as the overhead stone pressed down with relentless, crushing weight.
She pulled her slate from her apron and rested it against the timber. The internal gears clicked in the dark, the small brass arch catching the lantern light with a pale greenish glow.
‘Fourteen tons,’ Eren whispered, touching the splintered wood with his calloused fingertips. ‘The granite street above weighs five at most. The rest of that load isn’t stone. It’s deep water pressure. The drain tube overhead is leaking water into the porous fill between the vaulting and the street stone floor. The whole hill is becoming waterlogged.’
Pella unhooked her brass measuring tongs from her apron. She measured the gap between the bowed timber and the brick pilaster. ‘Three-eighths of an inch of clearance left before the beam binds against the brick,’ she reported, recording the measurement on her slate. ‘If the crown drops another half-inch, the timber will snap at the heartwood knot. When that happens, the third vault arch drops into the water.’
Sister Merrow bent down. She ignored the ache in her scarred knee. Then she scooped up a handful of the gray sludge swirling around her boots. She brought it to her nose, sniffing with a doctor’s cold and exact care. ‘Lime mortar. Crushed by heat. The water isn’t just pressing down, Eren. It’s dissolving the mortar between the bricks. In three days, this ceiling won’t be an arch. It will be a pile of loose red bricks held together by nothing but friction and prayer.’
‘Hal braced this sector after the flood,’ Merrow continued, wiping her palm on an oily rag. ‘The college told him the gallery was abandoned and didn’t need permanent stone vaulting. Hal told the High Warden that if the earth shifted, the ferry basin would cave in. He paid for these four oak balks out of his own pocket. The college never reimbursed him. Said it was a secret civilian improvement.’
‘He knew,’ Pella murmured. She touched the bowed wood again. She could feel the shaking through the grain. A high-hum tremor that made the splinters hum like harp strings. ‘He knew the college would try to run high-volume flow through the upper channel eventually. He braced this tunnel to protect the houses above, not the college.’
Sister Merrow reached into her canvas satchel and produced a strip of dried sheep’s bladder parchment stained with oak-gall dye. She dipped the tip into the warm water swirling past her shins. She held it up to the yellow light of the animal fat candle. The dark purple parchment right away bleached to a chalky, sickly orange. ‘Acid,’ Merrow muttered, her mouth set in a hard line. ‘Sulfur salt water from the deep shale beds. The high drain tube is pulling water from the fault-seams beneath the mountains, water that has sat under pyrites for ten thousand years. When you boil pyrites in a closed pipe, you get burning acid water. It will eat the nails out of Eren’s boots in an hour. It will dissolve the lime mortar between these bricks until they slide like butter.’
Eren took two dry oak wedges from his tool pouch and set them at the foot of the bowed timber. He raised his wooden mallet, aiming carefully in the flickering lantern light. With three sharp, ringing blows, he drove the first wedge into the gap beneath the doorstep plate. The sound echoed down the flooded hall like a hammer hitting an anvil. The timber groaned, settling an eighth of an inch onto the fresh oak face, taking a sliver of the strain off the split grain.
‘That will buy us twelve hours,’ Eren grunted, wiping sweat from his eyebrows. ‘No more. If we don’t bleed the water off the top of the vault, those wedges will crush into matchsticks before tomorrow’s noon horn.’
Pella knelt on a raised granite bench built into the wall—an ancient resting seat for watermen waiting out the spring spate. She scraped a thick layer of green slime off the stone with her iron scraper. She exposed the carved mason’s marks. Beside the guild mark, a series of level tally notches were cut into the stone, each notched with Roman numerals. ‘This bench marks the flood datum of Year -28,’ she said, laying her brass measuring tongs against the stone. ‘The river hasn’t reached this level in forty years without drowning the lower warehouses. But today the water in the harbor is low tide. Why is the water in this gallery running eight inches above the river surface?’
‘Because it can’t get out,’ Eren said, his voice grim. ‘The old river gate at the end of this run was fitted with cast-iron flapper valves to stop backflow during spring tides. If the flappers are jammed shut with river gravel, the water has nowhere to go. It backs up until it finds a crack in the ceiling.’
A sudden, sharp crack rang out from fifty paces deeper in the gallery. A sound like a pistol shot echoing off hard brick. Eren froze, his hand tightening on his mallet, while Merrow’s cane hit the water with a steadying splash.
‘Not the timber,’ Eren said after a tense, two-second silence. ‘That was baked-clay. A high-fired tile breaking under shear.’
‘It came from the drain tube junction,’ Pella said, her eyes narrowing as she peered into the dark steam fog ahead. ‘The chamber where the old ferry intake meets the lower bypass. We have to see what’s bolted to that line.’
‘Watch your footing,’ Merrow warned, her voice steady as an anchor chain. ‘If a baked-clay pipe splits while we’re in the bore, the hot water won’t give you time to say your prayers. Walk the centerline where the floor flags are solid.’
They advanced twenty yards, the gallery floor sloping downward at a steeper grade. The water deepened to mid-calf, the heat rising until it felt like stepping into a hot wash-tub. Up ahead, the narrow brick hall opened into a wide, circular chamber of dressed granite. An ancient water junction built in the city’s founding days.
In the center of the chamber, lit up by the rotten-egg yellow glow of trapped steam, sat a huge rig. A massive baked-clay trunk, four feet in width and glazed in dark green salt-slip, ran across the room like a dormant serpent. But bolted directly into its crown was a foreign, monstrous addition. An eight-foot collar of newly cast, polished bronze, clamped across the clay with heavy iron turnbuckles.
And from the bronze collar, a deep, rhythmic hum rang through the stone. A clockwork thrum so intense that Pella’s boot buckles shook against her ankles. ‘There,’ Pella whispered, raising her lantern. ‘That’s where the fever lives.’