The main transit conduit between the Western Vaults and the West Hangar was a vast cylindrical tunnel built from ribbed, unpainted industrial steel. In the early days of Aethelgard, it had served as a high-speed logistical vein, moving heavy machinery and structural materials across the city’s diameter on magnetic tracks. Now, with the power lines diverted to the upper escape convoy, the tracks were dead, cold iron ridges running through the gloom like the spine of a buried leviathan.I marched at the front of the column, my hand skimming the curved steel wall of the tunnel. The structural vibration was changing by the minute, growing sharper and more brittle as the countdown timer in my head ticked past the twelve-hour mark. Behind me, the seventy-level metropolis was a ticking bomb, its stabilizing magnets straining against the immense, crushing weight of the upper districts.Directly behind my shoulders came the vanguard. The fifty matte-black combat drones moved in absolute, terri