The forge beside Robert's house glowed dull red under a midday sky thick with iron-gray clouds. Heat pulsed in waves, the air sharp with coal dust and molten steel's bite. Leon hunched over a workbench, surrounded by a chaos of gears, springs, and metal scraps. Sweat streaked his brow, smudging the charcoal sketches pinned to the wall—tight, precise lines of a bow reimagined.

  Robert loomed nearby, arms crossed, cane tapping a steady beat against the stone floor. His scarred hands bore fresh nicks from the morning's labor, a silent mark of his aid. "Well?" he rasped, voice rough as gravel. "Show me what you've got."

  Leon straightened, wiping his hands on a rag. "It's not the final form," he warned, "but it proves the concept." He lifted a contraption from the bench—a sleek, foot-long frame of brass and iron, no wider than his forearm. A single steel coil gleamed at its heart, wound tight around a slim rod. A trigger jutted out, and a stubby barrel aimed forward. It was no archer's bow—no string, no sweep—but a machine, small and fierce, bristling with promise.

  Robert's brow arched. "That's your weapon?"

  "Observe," Leon said, a glint in his eye. He cradled the model, bracing it in both hands. His fingers turned a tiny crank, winding the coil eight full rotations until it thrummed—a sharp, taut hum like a wire at its limit. He aimed at a straw dummy ten paces off, its burlap chest sagging in the damp air.

  A flick of the trigger, and the coil unleashed. A bolt—short, thick, forged by Robert—shot out with a crisp snap, tearing through the dummy's center. Straw sprayed across the cobblestones, the bolt's tip buried two inches deep.

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  Robert limped closer, eyes narrowing. "whoa," he said, tapping the dummy with his cane. "Power?"

  "Calculated at roughly 120 foot-pounds of force," Leon replied, setting the model down. "Enough for leather or thin mail—say, 0.08 inches of steel. It's compact, so tradeoffs limit it. No plate armor yet."

  Robert grunted, studying the device. "Tradeoffs?"

  Leon nodded, voice crisp with numbers. "Three variables: mass, setup time, kinetic output. This weighs 2.3 pounds—portable, deploys in 4.6 seconds with eight crank turns. But the coil's diameter—1.5 inches—caps energy at 120 foot-pounds. Scale it to 3 inches, you'd get 300 foot-pounds, pierce 0.2-inch plate, but mass jumps to 7 pounds and winding takes 12 seconds. Unfeasible for quick use."

  "Then why build it?" Robert's tone was sharp, testing.

  "It's a proof," Leon said, meeting his gaze. "One coil at 120 foot-pounds proves the mechanism—energy stored, released in 0.02 seconds. The math holds. I can scale it—multiple coils, a 4-pound frame, 200 foot-pounds per shot. That's the target."

  Robert's lips twitched, a rare smirk. "One shot's a gamble. You're dead if it misses."

  "Correct," Leon said. "Probability of lethality's 0.85 at ten yards, drops to 0.6 at twenty. But no single device solves every problem. This coil's optimized for one purpose: catastrophic impact—120 foot-pounds in a single strike, built to shatter armor or bone with precision. For sustained threats, I'll need to design other devices—different tools for different equations."

  "Good," Robert said, planting his cane with a crack. "But sketches won't kill. Build it—every day, every flaw, you forge it anew. That's your pact, same as Michael's."

  Leon's pulse quickened, Chapter 8's vow sinking deeper. He eyed the dummy's torn chest—a promise of equations made real. "Yes, Father."

  Robert turned to the forge, stoking the coals with a nudge of his boot. "More steel. We've work left."

  Leon moved to obey, but lingered, hefting the model. It was small—far from the exoskeletal beast lingering in Leon's mind's eye. Yet this was its root. Outside, a breeze stirred the yard, whispering through the trees. Leon's thoughts spun—mass, time, power. Whatever lay ahead, he'd calculate an answer.