"Rule four, Levin," Sybilla had stated three weeks ago, pointing her brass pointer at a diagram of a carotid artery chalked onto the workshop floor. "When an uninvited adult offers you confections, what is the correct algebraic response?" Levin had raised a soot-stained thumb. "Pull lever green, drop sixty kilograms of scrap iron, then verify pulse with a broom handle." "Adequate," she had replied. "Remember: strangers are merely volatile variables waiting to be zeroed out." Now, Sybilla kicked the throttle of an ash-splattered freight hauler until the floorboards screamed. The iron chassis lurched across cobblestones, black exhaust churning into the lower ward’s smog. Beside her in the open passenger bed, Corso clung to the roll-cage with his organic hand while his rotary-cannoned prosthetic whirred, spitting spent casings into the gutter. "Slow down! We're going to roll this bastard into the drainage canal!" "Cap-screw tension allows for a four-degree margin of error on this gradient," Sybilla replied, shifting gears without touching the clutch. Metal ground like breaking teeth. "If my brother's life expectancy drops below ninety-nine percent, I am deducting the funeral costs from your prosthetic ammunition budget." "He's eight! Why do you talk about him like an inventory shortage?" "Because numbers do not deceive me, Corso. People, however, frequently require blunt force correction." Behind them in the cargo bay, Cosmina lay curled among grease rags, shrieking each time the wagon clipped an iron lamp post. "My dress cost two score sovereigns! Sybilla, tell him to steer! The silk is ruined! Drusian promised me a carriage with velvet lining!" "Throw her out if she alters the vehicle's center of mass," Sybilla said. Corso grimaced, though his knuckles remained white against the frame. "I'm not tossing your cousin into the street!" "Then gag her with a rag. Her acoustic output is degrading my navigation." They skidded into the alley fronting the Lower Ward bunker. The blast-door hung off its upper hinge, heavy steel scorched black where an explosive charge had bitten through the outer lock. Sybilla was out of the cabin before the wheels ceased spinning, an eighty-millimeter spanner resting against her collarbone. Corso swung his legs over the sideboard, his mechanical joints locking into position as he hauled his customized rifle forward, the skin tight across his scarred temple. "Levin!" They breached the threshold. Sybilla took point, boots stepping clean over tripwires she had strung two days prior. Silence answered them, save for the hum of the auxiliary turbine and the rhythmic crunch of sugar crystals. In the center of the living quarters, suspended three meters above the stone floor by a counter-weighted titanium cargo net, Uncle Yvan hung upside down like an overfed hog bound for market. His velvet coat was torn, his powdered wig rested in a pan of dirty motor oil below, and a dozen tiny iron caltrops were embedded in his leather boots. Sitting on an overturned crate underneath him was Levin, humming an Upper Tier nursery tune while eating peppermint drops with grease-blackened fingers. "Levin," Sybilla said. "He had lemon candies," the boy reported, not looking up from his tin. "I pulled lever green. But the iron scrap missed his head, so I pulled the blue crank instead. The winch worked." "You wasted three seconds between decisions," Sybilla noted, inspecting the tension cables. "However, the target is secured without property damage to my bookshelf. B-plus." "Sybilla!" Yvan bellowed, his face plum-purple from inverted circulation. The genial uncle mask had vanished; spittle flew from his bared teeth. "You insolent little clerk! Cut me down! Do you have any concept of who holds the debt notes on this sector? You think this metal rat of a husband makes you safe?" Corso leveled his barrel straight between Yvan's eyes, his shoulder rigid. "Shut your mouth, Yvan. Or I'll see how many holes this frame takes before it snaps." Yvan did not flinch. Instead, a wet, rattling laugh spilled out of his throat, spattering the floorboards. "Shoot me, veteran. Pull the pin. It won't change the dials in the sub-floor." Sybilla looked down instantly at the brass floor-grates. Thin wisps of sulfurous vapor were curling upward, hissing against the cold stone. "What did you do?" she demanded, her voice dropping an octave into chilling neutrality. "I didn't come here just to take the boy," Yvan wheezed, grinning through bloodied teeth. "I knew you’d turn the foundry against my men. You're too paranoid to die quietly. So I bypassed your regulators. I tapped the primary geothermal riser below your floor and jammed the exhaust baffles with slag-wedges." Corso went gray beneath his engine grease. "The bedrock fissure..." "In four minutes, the subterranean pressure will crack the foundation," Yvan sneered, thrashing in the netting. "The entire city block will collapse into the boiling vents. Your deeds, your patents, your miserable little family—all incinerated. The Land Registry bylaws state that unrecovered estates default straight to the nearest surviving paternal kin through my offshore consortium. Even if I swing here, my executors take every brass farthing! You lose, Sybilla! Your math failed!" A shrill alarm screamed from the wall console. The primary gauge needle had slammed past the red index, trembling violently against the brass stop pin. "Levin, take your peppermints and exit to the transport vehicle," Sybilla said evenly. "Yes, Sybilla." "Corso, escort him and ensure Cosmina does not pawn the spare tires for pastry." "Wait—no!" Corso grabbed her wrist, his iron grip surprisingly firm despite his trembling. "You can't vent it from up here. The safety manifold is in the sump room below the furnace!" "Correct," she said, unclipping a heavy brass spanner from her belt. "Which is why I am going down." "Are you insane? The secondary seal ruptured ten seconds ago!" Corso pointed toward the lower hatch, where superheated vapor was already whistling through the seams, peeling the enamel off the bulkheads. "The chamber is flooding with superheated vapor at five hundred degrees! The moment you turn that wheel, the blast will cook your lungs before you can draw breath!" Sybilla looked at the dial, then met his gaze her pulse steady at sixty beats per minute. "A sixty percent chance of third-degree burns versus a one-hundred percent chance of total financial and biological liquidation," she stated, ripping her arm free. "The arithmetic does not permit negotiation." She grabbed the hatch lever and hauled it upward against the screaming white vapor.

The Geothermal Gambit