Eren Tal sat on an overturned herring barrel three feet from the weeping wall, his drawknife laid flat across his knees. A six-inch pine shingle rested on the rough timber bench beside him, alongside a stick of vine charcoal, a carpenter’s brass scriber, and a horn pot of dark oak-ink.
Every four seconds, the needle on the brass dial kicked.
Clack. Forty-two. Drop. Eighteen. Clack.
To a carpenter, four seconds was not an abstraction. Four seconds was the time it took an eighteen-foot ash waterwheel to make one quarter of a revolution at high mill-tide. It was the rhythm of a balanced pit-saw running through four inches of green oak under two men’s weight: pull down, push up, clear sawdust, catch the stroke.
Eren adjusted his iron-framed glasses. Cheap ground glass he had bought from an itinerant tinker on Fish Street, held together at the bridge by a wrapping of copper wire. He leaned forward until his face was eight inches from the gauge glass.
With his left hand, he held a dry pine peg above the shingle. Every time the black needle hit the red grease pencil mark Ada had drawn at forty-two pounds of pressure. His thumb was pressed the charcoal into the grain. It drew a short, upright hatch mark.
He had five rows of twenty hatches already scored into the wood.
“It doesn’t drift,” Eren said, his voice flat with the concentration of a man truing a wheel hub. “An hour ago, I thought it was tied to the river swell. When the big heavy cart barges come down from the upper lock, they push a three-foot wave into the South Cut. But a river surge has a long shoulder. It comes in slow, holds for twenty heartbeats, and slips away like grease.”
Across the washroom, Pella stood at the bread table, using a piece of foam-stone to grind down an old ink crust on a sheepskin receipt. The smell of boiled tea drifted from the hearth, mingled with the earthy silt stench that rose from the open floor drain.
“Ada said it was governed,” Pella remarked, looking up. “A clockwork discharge.”
“Not just one valve,” Eren said, pointing the charcoal stick at the board. “A single valve on a quirky cam opens and closes on a full cycle. If you had one pump or one blowdown cock, you’d have a spike, a long decay as the pressure vented down the line. Then a pause while the pressure built back up in the vessel. You wouldn’t get a four-second repeat. A steam vessel that size couldn’t reheat and rebuild forty pounds of head in four seconds.”
Sister Merrow set down her iron ladle by the broth pot and walked over. She wiped her damp forearms on her canvas apron. Her sleeves were rolled past her elbows, showing the thick, puckered white lines of old shrapnel cuts from her years on the field hospital barges.
She looked at Eren’s rows of charcoal tallies. “Then what’s making the four-second beat, wheelwright?”
“A distributor,” Eren replied, tapping the brass scriber against his thumbnail. “Think of a four-spoke water gate. If you have four separate pressure vessels on the hill, and each one vents once every sixteen seconds. But they’re geared to a single turning shaft with their release cams offset by ninety degrees... What do you get down here?”
Pella stopped her foam-stone. “A pulse every four seconds.”
“Four seconds on the dot,” Eren said. “One vents, drops to eighteen. Before the line can drain, the second vessel trips. Then the third. Then the fourth. It’s a rotary pipe hub. And there’s only one place in Lathmere that has the bronze machinery to run a four-phase rotary discharge.”
“The High Sluice Crown,” Merrow said, her voice dropping into a dangerous, dry rasp.
“The High Sluice Crown,” Eren confirmed. He rose from the herring barrel, stepped over the catch-bucket. Then he placed his palm against the wet stonework. The stone block directly above the lead collar was warm—not lukewarm, but hot enough to dry out the water drops in a pale, powdery ring around his fingers. “The College built the Crown to drain the Great Upper Terrace. They told the High Council that the overflow dropped through the mountain under-road drains into the outer bay. But mountain under-road drains cost gold to blast through granite. Running a secret lead drop down the old spine of Lowbank costs nothing.”
Merrow didn’t answer right away. She picked up an iron oil lantern from the wall hook, trimmed the linen wick with her thumb until the flame burned clear and yellow. Then she held the light six inches from the wall surface.
The stonework around the lead main was rough limestone rubble, bedded in coarse grey mortar that had crumbled into sandy pipe lime wherever the hot steam had pierced.
“Look at the header course,” Merrow said. She pointed the lantern base at the long, box-shaped top door beam stone that spanned the four-inch pipe collar.
Eren leaned in, adjusting his wire glasses. The surface of the stone had been dressed with a tooth-chisel, leaving narrow, slanted furrows across the grey face. In the lower left corner, half-hidden beneath a hardened crust of white lime, three tiny three-sided marks had been punched into the stone with a center-punch.
The marks formed an open triangle with a level bar beneath: a ferryman’s hitch.
Eren’s chest tightened. He knew that mark. Every oak cart-bench and heavy cart axle that had come out of Hal Rook’s shop between the two great floods carried that matching three-cornered punch.
“That’s Hal’s mark,” Eren whispered.
Pella dropped the foam-stone. It fell onto the table with a dull thud. She crossed the flat stone slabs in three quick strides, stopping beside Merrow’s elbow. Her hand reached out, her trembling fingers brushing the lime crust away from the three punched depressions.
“My father dressed this stone?” Pella asked, her voice barely heard above the hiss of the drain.
“He didn’t just dress it,” Merrow said grimly. She held the lantern steady so the yellow light caught the edges of the chiseling. “He laid it. Fourteen years ago, during the week of the Great Breach. The water was rising three inches an hour in the lower ward. Then, Master Sorell came down from the college with six armed wardens. They took Hal from the ferry landing at midnight. They said there was an emergency wooden props job in the deep under-road drains that only a master carpenter and boatwright could frame.”
“I remember that night,” Pella said, her eyes fixed on the three-sided mark. “He kissed my forehead. He told me he would be back before the morning bread was drawn from the ovens. Two days later, Sorell’s clerk brought us three silver pieces and told my mother that Hal had been caught in a stone cave-in beneath the North Bastion.”
“There was no cave-in beneath the North Bastion,” Merrow said, her jaw tight. “The North Bastion stands on solid whinstone. I treated two of the wagon drivers who hauled the mortar barrels that night. They were swearing under their breath about a sealed gallery behind the sculleries. Sorell didn’t bring Hal down here to fix a flood breach. He brought him here to encase this high-pressure bypass in stone so no one in Lowbank would ever know where the boiling discharge was dumping.”
Eren ran his fingers along the mortar joint above Hal’s mark. “And then they sealed the gallery.”
“They sealed the gallery,” Merrow said, “and twenty-four hours later, the main under-road drain blew its arch, forty families drowned on Fish Street, and Hal never came back out of the hole.”
The needle on the brass gauge struck forty-two with a sharp, metal ring.
Clack.
The sound, which ten minutes earlier had seemed like an annoying clockwork puzzle, now sounded to Eren like an iron knuckle rapping on a tombstone.
“They used him to hide their pipe,” Eren said. His voice dropped an octave into cold, controlled fury. “And then they left the line live. For fourteen years, they’ve been blowing their potion-made stills and their laundry boilers into this wall, letting the heat eat the mortar, waiting for the day the lead tears and washes away the evidence.”
“They didn’t expect someone to put a gauge on it,” Pella said. She reached out, her hand resting firmly on the cool ash timber shore that Eren had wedged beneath the ceiling. “They expected us to do what Lowbank has always done: burn incense, complain about the mud, and pay three coppers a hearth to the purification fund.”
Eren picked up his vine charcoal, turned back to the pine shingle. Then he drew a thick, heavy box around the last column of numbers.
“Four seconds,” he said, writing the numeral with deliberate, digging strokes that crushed the charcoal into the soft wood grain. “Peak forty-two. Low eighteen. Heat one hundred and forty degrees.”
He looked at Pella. His anger had not evaporated. But it had settled into the hard, practical discipline of his trade. A warped timber couldn’t be planed true with tears. It had to be clamped, steamed, and held to the line with iron dogs until it yielded.
“We don’t break the wall with a sledge,” Eren said, repeating Ada’s instructions word for word. “Ada was right. If we smash that header stone, the lead blows out and we lose the back kitchen. But tomorrow noon, when that arch opens, we don’t just ask her how to bleed a pipe.”
“What do we ask her?” Pella asked.
Eren pointed the blackened tip of his finger at the brass gauge.
“We ask her how to trace a pipe hub back to its valve. If the College of Summoners thinks they can pump their poison into Hal Rook’s stone forever, they’re about to find out what happens when you block the outflow.”