The magma surge gave no warning. One moment the passage floor was warm but stable underfoot, the Ash Ridge Badlands' standard geothermal background. The next, the stone beneath Marcus's boots cracked along a fault line that ran the width of the tunnel—and through the crack, orange light blazed upward with a heat so intense it felt like opening an industrial furnace.
"RUN!" Marcus shouted.
The crack spread behind them at speed—not the slow geological process of normal tectonic movement but an explosive decompression event, the mercenaries' repeated seismic charges having fractured the pressure seal on the primary thermal vault three kilometers deeper in the fault system. The magma was not flowing so much as erupting upward through stress-fractured rock, filling passage sections from the floor upward with liquid basalt at twelve hundred degrees.
Talon was already at full sprint—not panic, but the calibrated, economical flat-out run of a predator who had survived underground emergencies before. His echolocation was operating at maximum frequency, scanning fifty meters ahead at a rate that would have registered as acoustic noise to any instrument, his sickled claws striking sparks from the basalt floor with each stride.
Marcus ran behind the raptor, his acoustic sensor abandoned in his vest pocket, his entire attention on not losing sight of Talon's amber feathers in the strobing orange-lit darkness.
Behind him, the magma surge filled the section they had just vacated with a sound like a river of stone. The passage branched—Talon went right without slowing, his body canting at the turn with fluid raptor efficiency, claws finding grip on the angled floor instantly.
The right branch climbed. Steeply.
The magma followed the path of least resistance through horizontal passages, but a steep upward climb bought them time—liquid rock moves slower against gravity than across it.
Marcus climbed. His lungs burned. The air temperature had jumped fifteen degrees in thirty seconds, and the moisture that had characterized the deeper passages was gone, replaced by dry volcanic heat that made each breath feel insufficient.
Reyes stumbled on a section of cracked floor. Marcus caught her arm without breaking stride—momentum was survival here, momentum and Talon's echolocation and thirty seconds of lead time over rising lava. Patel was behind them, his geological sensors abandoned, running with the single-minded focus of a man who had spent enough field hours in unstable geological zones to know exactly how bad this scenario was.
At the top of the climb, the passage opened into a wide, roughly circular chamber—and Talon stopped. Not panic-stop. Assessment stop.
The raptor scanned the chamber with its full acoustic toolkit. Marcus reached it fifteen seconds later and bent over his knees, hauling air into his lungs. Below them—audible now, a deep, thunderous rushing—the magma surge was moving through the passages they had just climbed.
Three exits from this chamber. Talon checked each one in sequence, directing pulses down each passage in turn, reading the thermal return profiles. One passage returned a surge heat signature: the magma had found it.
One returned neutral heat: accessible but it was a dead end—the acoustic echo returned from a wall three hundred meters down. The third returned a faint but unmistakable signature: cooler air. Moving air. The signature of a chimney opening to the surface.
Talon moved to the third passage, clicked twice, and looked back at Marcus. Three hundred meters below them, the magma surge filled the lower tunnel network with the sound of the earth's interior made briefly visible. They had minutes.