"He's lying," David said, his eyes never leaving Vance's face. "The master key doesn't cycle the hatch. The master key turns the mechanical bypass valve on the exterior manifold. If you give him that key, he opens the drain to the quarry, the contaminated wash hits the culvert, and he seals the intake forever."
"And if you don't give it to me," Vance shouted, stepping back toward the van where the two mechanics stood frozen in the headlights, "Mark stays in that hole!"
I looked down at the brass key in my hand, then at the heavy steel bulkhead doors set flat into the concrete apron ten feet away. Around the perimeter of the hatch ran four high-pressure hydraulic dogging bolts, each driven by an internal solenoid tied to the supervisory board. Next to the hatch was a manual mechanical release box, secured by a heavy brass padlock stamped with the identical five-digit code: PA-DWR-04-B.
"He didn't bolt the hatch from the inside," I said, looking Vance straight in the eye. "These bulkheads don't have interior dogging levers. State water code requires all lower gallery access hatches to lock strictly from the outside to prevent operators from being trapped during a surge. You dogged that door yourself before your crew went to the station locker."
Vance didn't answer. He lunged forward, swinging the heavy metal Maglite in a flat, vicious arc aimed straight at my collarbone.
David hit him before the light could reach my shoulder. He drove his shoulder hard into Vance's chest, knocking the older man backward across the slick concrete. The flashlight flew from Vance's grip, skittering across the apron and plunging into the black water of the river intake pit with a hollow splash.
Vance hit the wet asphalt hard, scrambling on his hands and knees, reaching into the deep pocket of his slicker for his utility radio. "Lock them out!" he screamed at the two mechanics standing by the hoist. "Hit the manual purge button on the van console! Do it now!"
Neither mechanic moved. The man who had been holding the hoist chains stepped backward, his hands held high, his eyes wide as he looked at the Mid-State invoices fluttering on my clipboard under the headlights. "Not for this, Harold," the mechanic said, his voice shaking. "We were hired for pipe fitting. We aren't doing manslaughter."
The mechanic turned and ran, disappearing into the dark brush along the railroad easement.
David had Vance pinned by the collar of his slicker against the lower step of the concrete stairs. Vance was thrashing, his boots slipping in the mud, his teeth bared in a snarl of exhausted rage, but David held him down with both forearms, his torn red custody band pressed hard against Vance's throat.
"The release box," David shouted over his shoulder to me. "Thomas, open the release box!"
I didn't waste a second. I dropped to my knees on the wet concrete beside the steel hatch. The rain was coming down harder now, stinging my eyes as I shoved the heavy brass key into the padlock on the mechanical release housing.
The lock was cold and stiff with river grit, but the brass teeth bit clean into the internal tumblers. I put both hands on the key and leaned my entire weight into the turn.
With a sharp, iron snap, the padlock sprang open.
Inside the housing was a single red cast-iron wheel connected to a high-pressure hydraulic bypass cylinder. Painted in white stenciled letters across the steel backing plate was the emergency instruction: PULL AND ROTATE CLOCKWISE TO DUMP SEAL PRESSURE.
Above us, the high-frequency horn on the station roof began to wail—a shrill, piercing pulse that signaled the start of the midnight purge cycle.
Deep inside the concrete vault, the sound of the pipe wrench stopped. In its place came the terrifying, hollow shriek of four-inch relief valves opening under ninety pounds of river pressure, followed immediately by the dull, thunderous roar of raw water surging into the lower intake chamber.
"It's filling!" David screamed, holding Vance's thrashing shoulders against the concrete. "The water's hitting the floorboards! Turn the wheel!"