The pulse chased them up the shaft.

  It was not sound. It was pressure rolling through metal and growth in waves, making the rungs shiver under Vega's hands. Her teeth buzzed. The lights inside the vein-like strands along the wall flashed faster, running in jagged sequences instead of the slow rhythm from before.

  "Do not stop," Vega said. "Hands and feet moving. We are outrunning a nervous system that just got stabbed in the heart."

  "Alpha clear of the cavern lip," Park reported from above. "No contacts on my level yet. Growth is… moving. Faster."

  "Define moving," Watson said, just ahead of Ito.

  "Pulsing, shrinking in some places, bulging in others," Park said. "It is like watching a muscle spasm."

  The shaft glowed around them, the veins strobing green and blue with violent intrusions of red. In places, new tendrils pushed out of the wall, thin and questing, reaching toward the ladder and the human shapes on it.

  One brushed Vega's boot.

  Sensors flared, suit systems dumping a microburst of neutralizing charge through the outer layer. The tendril jerked back as if stung, its internal lights flaring white, then going limp.

  "It is reacting to us," Ito said, breathing hard. "We are not just intruders in its nest anymore. We are tagged."

  "Up," Vega said. "Argue classification later."

  They climbed.

  Meters ticked past on her HUD. Ninety. Eighty-five. Eighty. Vega did not look down. She focused on the next rung, and the next, and the way her gauntlets closed around solid metal.

  At seventy-five meters, the first change hit.

  The shaft narrowed.

  Not in rock—the walls stayed where they were—but the growth had thickened across one section of the well, swelling into a ridged band that pinched the available space.

  Park reached it first. "Blockage," she said. "Partial. I can squeeze through. Might not like it."

  "Options?" Vega asked.

  "Cut it," Park said. "Or push. Cutting might piss it off more."

  "This is not a democracy," Vega said. "Push."

  There was a brief pause, then Park grunted. "Through," she said a moment later. "It is like squeezing through a wet barrel. Suit integrity holding. It… tightened when I went past."

  "That is comforting," Watson muttered.

  "Next," Vega said.

  Watson's turn. He swore steadily under his breath as he forced himself into the constricted section. The growth flexed around his shoulders and hips, indenting slightly. Lights inside it flared bright around his silhouette.

  "Feels like it is taking my measurements," he said through clenched teeth. "If it asks for a dance, I am resigning."

  "Keep moving," Vega said.

  Ito went next, grunting once as the growth rippled around his equipment pack. His scanners squealed in protest, then recalibrated.

  When Vega reached the constriction, she did not hesitate.

  She drove one shoulder into the tightest part and shoved. The growth had a disconcerting give, like thick muscle or tightly packed roots under a rubber sheath. It pushed back. For a moment, she had the sensation of something examining her in return, a pressure that was not purely physical running along the curve of her armor.

  Her suit's external fields flared. The lights in the growth flashed rapidly, then dimmed a shade.

  "Captain?" Ito called.

  "Through," she said. "It is learning. We are not making friends."

  At sixty meters, the atmosphere thickened further.

  Readouts scrolled warnings across her visor: particulate density up, spore analogs higher, electromagnetic noise saturating their band. Ito cursed as his rig dropped half its external feeds.

  "I am losing long-range coherence," he said. "It is all static and local echo. Whatever brain this thing has, we are inside its interference pattern now."

  "Short-range comms?" Vega asked.

  "Still good," he said. "For now."

  They passed the first of the side tunnels they had seen on the way down.

  It was worse.

  The lattice that had filled the passage earlier had thickened into a solid wall, every gap plugged, the entire surface shivering with faint, coordinated movement. Pale nodules swelled along some strands, pulsing like blisters.

  A thin crack ran through the center, no wider than a finger. Hot, moist air hissed through, carrying a smell so dense and organic that even through filters, Vega's body recoiled.

  "Do not put anything into that gap you want to keep," Watson said.

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  "Noted," Park replied.

  They climbed past.

  At fifty meters, the shaft shook.

  A deep, grinding tremor rolled through the rock. Dust and flakes of dried growth rained down from above. Somewhere far below, a muffled roar echoed up, then cut off.

  "Explosion?" Park asked.

  "Not ours," Ito said. "Our charges are cold. That was something structural. The organism is moving mass around. Or something collapsed."

  "Do not let it knock you off," Vega said. "We drop from here, we skip the part where we die screaming and go straight to the splat."

  They rode the aftershocks out, muscles locked, hands aching on the rungs.

  At forty meters, the first Vectar above them made itself known.

  Park saw it.

  "Movement at the top of the shaft," she said sharply. "Something just crossed the opening. Fast."

  "How many meters?" Vega asked.

  "Estimate ten above the Sublevel One threshold," Park said. "It is hugging the wall. I saw the tail."

  Vega pictured it: a Vectar clinging upside down or sideways around the mouth of the shaft, waiting for the first helmet to rise into reach.

  "We do not have room for a firefight on the ladder," Ito said grimly.

  "No," Vega said. "We do not."

  She thought fast, brain running geometry and timing.

  "Park," she said, "hold at thirty meters. Do not go higher until I say."

  "Yes, Captain."

  "Ito, can we push a surge up the spine?" she asked. "Short, sharp pulse."

  "Maybe," he said slowly. "If I piggyback off the growth's own conduction. Why?"

  "Because we need that Vectar off the ceiling," Vega said. "If we hit the spine hard enough to make this thing twitch, maybe it shakes our friend loose or at least distracts it long enough for us to get guns above the edge."

  Ito was quiet a moment. "I can route a concentrated pulse through the charge network," he said. "Not enough to trigger detonation, but enough to make a lot of unpleasant noise in its nervous system."

  "Risk?" Vega asked.

  "It may accelerate whatever reaction we already started down below," Ito said. "The spine could spasm. We could get more structural shifts." He hesitated. "And it will know exactly where we are touching it."

  "It already knows we exist," Vega said. "We need space. Do it."

  Ito braced on the ladder, one arm looped through a rung so he could work with his free hand. His gauntlet interface flickered as he linked to the charges and the organism around them.

  "Routing," he murmured. "Shunting. Setting amplitude. On your mark, Captain."

  "Park," Vega said, "get ready to move the instant the shaft opening shifts. You see a limb, you take it."

  "Understood."

  Vega took a breath, tasting recycled air and old adrenaline.

  "Mark," she said.

  Ito sent the pulse.

  For a heartbeat, nothing happened.

  Then the world convulsed.

  The growth along the shaft walls flared white. The veins bulged, then contracted violently, forcing bioluminescent fluids through their channels. The mat below shuddered. The entire ladder flexed under a sudden, unseen strain.

  Vega gritted her teeth and held on.

  Above, something screamed.

  The sound knifed down the shaft, half mechanical, half raw animal pain. Scrabbling followed, as if multiple limbs had lost their grip at once.

  "Now!" Vega shouted.

  Park surged upward, taking the last meters in a fast, dangerous climb. Her helmet crest appeared at the mouth of the shaft an instant later, rifle already rising.

  She caught the Vectar as it flailed.

  It had been clinging sideways just above the opening, tail coiled. The pulse had hit it like a hammer, sending its limbs spasming. It scraped at the shaft lip, claws gouging metal as it tried to anchor itself.

  Park did not give it time.

  She fired point-blank into the nearest cluster of eyes.

  The shots blew out half its face in a spray of shattered armor and luminous matter. The scream cut off mid-note. The creature's grip failed.

  "Dropping!" Park barked.

  "Hold!" Vega snapped. "Do not get under it!"

  The Vectar fell past Park's position in a blur of limbs and plates.

  For a split second, it filled Vega's field of view: a tumbling mass of chitin and light, tail thrashing, darts firing blindly. One dart pinged off Vega's raised buckler and caromed away. Another clipped the shaft wall and exploded in a shower of corrosive spray.

  Then the creature was past, falling into the depths.

  Vega listened.

  The impact came seconds later, a brutal, wet crunch that echoed back up with a delayed spray of flecks and fragments. Her HUD showed a brief spike in particulate contamination, then leveled off.

  "Next problem," Watson said shakily. "If that thing hit the charges—"

  "It did not," Ito said. "The charges are on the chamber and nodes. The shaft is clear. But the organism knows we just stuck a finger in its brain."

  "Then we pull the finger out and get out of its head," Vega said. "Park, secure the opening. Two meters up, then clear to Sublevel One. We are right behind you."

  "Moving," Park said.

  They climbed faster now, urgency burning in every muscle.

  At Sublevel One, the shaft opened into another reinforced corridor. Here, the growth was thick but not yet solid. Strands looped along ceiling and walls, nodes pulsing like infected glands. The floor was still mostly visible metal, veined with delicate tendrils.

  Park crouched just inside the opening, rifle aimed down the hall. "No contacts close," she said. "But the whole place is… twitching."

  "Up and out," Vega told the others. "Quick."

  One by one, they hauled themselves out of the shaft and into the corridor. The air felt marginally less dense here, though still tainted. Suit filters whirred steadily.

  Ito checked his displays and pointed. "Stairs to the main level are that way," he said. "If they have not caved in."

  "Then that is our vector," Vega said. "We are not stopping between here and control unless something big blocks the way. Move."

  They ran.

  The corridor bucked under their boots as more distant tremors rolled through the structure. Overhead, the lights flickered or died. In the dark gaps, the glow from the growth brightened, eager to fill the void.

  They hit the stairs and pounded up them two at a time.

  Here, the organism was less dense but still present. Veins snaked along the handrails. Slime coated some steps. A few new tendrils reached for their ankles, reacting to the vibrations of their running feet. Armor and speed carried them past.

  "Contact ahead," Park warned.

  At the top of the stairs, the corridor to refinery control yawned open. A Vectar blocked it, smaller than the one below but no less vicious, tail arched, mandibles clacking.

  This time, there was room to move.

  "Alpha left, Bravo right," Vega said without breaking stride. "Cross it, do not stop in front of it."

  They split at the landing.

  The Vectar lunged at the largest concentration of motion: Watson's side. Vega swung her buckler up and slammed into its flank as she crossed in front, turning its charge just enough that its darts went wide.

  Park and two others tore into its side. Rounds shattered leg joints. Armor plates blew out. Ito snapped a shot into the base of its tail, severing the dart cluster in a spray of luminous debris.

  By the time Vega reached clean floor beyond it, the Vectar was thrashing, half crippled.

  "Do not waste rounds," she said. "You know the drill."

  Watson, breathing hard, stepped in close and shoved his carbine under its raised limbs, into the softer segment around its underbelly.

  "This is for Bravo Two," he said, and fired until the magazine ran dry.

  The creature spasmed once more and went still.

  "Tag it for later," Vega said. "We do not have time to burn this one."

  They pushed on, boots leaving smeared tracks of alien fluids as they ran.

  The message on the lobby wall—DO NOT GO BELOW—gleamed dully as they passed it on the way back toward control. The letters seemed to watch them, accusation written in dried blood and something else.

  "We went anyway," Watson said under his breath.

  "We had to," Vega said. A tight beat of doubt slid through her chest, then she shoved it down. "Now we get to see if it matters."

  The doors to refinery control loomed ahead.

  Beyond them waited the beacon Park had left, the route back to the surface, and, if the storm and the organism had not finished the job yet, a landing zone that might still be in one piece.

  Behind them, deep below, the charges nestled against the Vectar's spine like seeds of a different kind of growth, waiting for a spark.