They were three hours into the central cavern crossing when the mercenaries found their own way in. The seismic charge detonation was different from the earlier ones—targeted, shaped, designed to open a specific geological formation rather than simply pulverize.
Marcus felt it through the floor before he heard it: a sharp, directional pressure wave that propagated through the mineral sediment from the north wall of the central cavern, followed two seconds later by the sound of a large section of basalt wall collapsing inward.
Dust and rock debris billowed across the cavern floor in a rolling gray wave. The alpha Deinonychus let out a twenty-two-hertz alarm pulse so powerful Marcus felt his vision vibrate, and every living thing in the central cavern that Marcus had been slowly detecting with his acoustic sensor began moving—away from the collapse, into the deeper cavern passages.
Through the dust cloud and the new breach in the north wall, lights appeared.
Professional tactical lights—the kind attached to military-grade personal equipment. Then voices, radioing coordinates in clipped professional language. Marcus grabbed Talon's shoulder and pulled back toward the eastern passage entrance.
"Move," he said to Reyes and Patel. "Now. Quietly."
They moved. Behind them, through the dust, Marcus heard the mercenary team's acoustic mapping equipment activate—a different kind of echo system, mechanical rather than biological, but doing the same job: building a spatial map of the cavern from acoustic returns. They were going to locate every living organism in the space within minutes.
Talon understood the urgency faster than any of the humans. The raptor moved at half-running pace through the eastern passage, pulse set to focused close-range navigation, threading turns and low sections with fluid efficiency. Marcus followed three steps behind, torch dimmed to its minimum setting—enough to avoid obstacles, not enough to be visible from distance.
The eastern passage narrowed sharply at its mid-point, squeezing down to a section barely wide enough for single-file human passage. Talon went through at a diagonal, folding his limbs with surprising dexterity—the ecology of the narrow lava tubes had clearly driven body flexibility in the species across generations.
When Marcus reached the narrow section, he turned sideways and pressed through—and heard, resounding behind them in the central cavern, the sound of the mercenary team deploying a secondary seismic sensor array.
They're mapping the entire system, Marcus thought, pressing through the tight stone. Not just looking for us. They're surveying every passage. Building a complete extraction map.
He emerged on the far side of the narrow section and kept moving. Patel was behind him, breathing hard. Reyes was last, checking behind them each time the passage widened enough to turn.
Talon paused at a passage junction—four tunnels diverging in different directions—and stood with his pulse on high-frequency scan for thirty seconds. His head moved in small, precise arcs, interrogating each tunnel with directed sonar. Then he chose the right-descending tunnel, clicked twice, and moved.
Down. Going deeper meant moving further from any surface exit. But it also meant moving into geological territory so complex and geothermally active that no mechanical sensor array designed for surface mining operations would function reliably.
He's taking us where their equipment can't follow, Marcus understood. He followed Talon into the descending dark.