Ahead, he saw five figures in yellow power armour beneath a hole blasted in the cavern roof, standing in a ring of dead bodies. Two Space Marines were advancing towards him, while the others prepared explosives to bring down the tunnel before it could reach the citadel's wall. Forrix opened fire before they saw him, the sound of his weapon deafening in such a confined space. One Imperial Fist dropped, a series of red craters torn in his breastplate.
Ricochets blew out the glow-globes, sputtering light casting lunatic shadows over the tunnel walls. The second Space Marine dropped into a crouch and returned fire with his bolt pistol. The impacts hammered against Forrix's breastplate, but Terminator armour had been designed for just this kind of close-quarters fighting and not a single bolt could penetrate the thick armour.
Forrix shot again, swinging his power fist. The warrior ducked and rolled aside, Forrix's blow smashing apart an iron prop and pulverising a huge section of wall. Rock and dust filled the air as he rounded on his opponent. The Imperial Fist drew a sword, its blade wreathed in amber fire, but die tunnel was too cramped to wield it effectively.
Forrix batted aside the blade and pistoned his fist through the warrior's chest, smashing his ribcage and ripping out his heart and lungs. He pushed aside the bloody corpse, stepping into the main gallery and spraying the Imperial Fists with bolter fire. One man dropped, blood washing down his thigh as the others dived for cover. Bolter fire blasted the rock around him and pounded his armour.
Somehow a bolt found its way through his shoulder guard and blood started to pour from a wound in his arm. He roared in anger and emptied the remainder of his bolter's magazine into the nearest Imperial Fist, the snap of the hammer dropping on an empty chamber shockingly loud in the cramped tunnel.
Behind him, Forrix could hear the shouts of approaching soldiers. His bolter empty, he pulled back the arming slide on his combi-weapon's other armament fixture.
The last Space Marine rose from his cover and opened fire, hosing Forrix with bullets. Forrix rocked under the impacts, bringing his weapon to bear and fired the underslung melta gun. The white-hot blast of superheated air punched into the Imperial Fist, incinerating his torso with a hissing detonation, the oxygen-rich blood in his body flashing to a stinking red steam.
A pile of armoured limbs and a head - all that remained of the Space Marine - clattered to the floor, the gory stumps cauterised and molten. Forrix dropped his weapon and swept up a fallen bolter as red-clad human soldiers raced to join him from the surface.
Suddenly, Forrix caught the stench of something vile from the opening in the cavern roof and realised he had to get out of here. He turned from the rockface and ran past the startled soldiers without a word. He ran as fast as he could back towards the surface, but as he heard the roaring thunder behind him, he realised he wouldn't make it in time.
Forrix lurched left into one of the deception tunnels. He heard screams from behind him and knew that every soldier down here was a dead man. The roaring grew louder, magnified by the closeness of the walls.
Forrix continued down the side tunnel, ducking round a bend as the first rush of chemicals swept towards him.
A tidal wave of poisoned chemical waste thundered through the tunnels, diverted from every culvert, septic tank, latrine and night-soil pipe in the citadel. Forrix had smelled the reek of the waste and the acrid tang of the bio-toxins. He clung onto the rough walls as the foul, liquid effluent roared through the tunnels, sweeping all before it.
Men were crashed to death against the rocky walls as the vile solution pummelled them, filling the tunnels with excremental fluids. Those not killed by the first tidal wave were drowned or poisoned in the toxic waste as it rose to the ceiling, shorting out the remaining glow-globes and snuffing them out one by one.
Sheltered from the worst of the flood in the side tunnel, Forrix hung on as the grey-brown sludge sloshed around him, rising higher with each second until he was immersed in the thick tide. He knew he was in no danger, his armour was proof against the hard vacuum of space and it had suffered worse fates than this in its long life.
How far up the tunnel the flood of liquid would reach, Forrix had no idea, but guessed it could not be too far. To effectively flood the tunnels, this amount of waste would have had to have been diluted with much of the garrison's drinking water. Perhaps, believing their salvation had arrived in the shape of the Imperial Fists, the defenders thought they could afford to be cavalier with their water supplies.
A few minutes passed before the tunnel began to drain. The Imperials' plan had failed. Forrix had built scores of such mines and had had more lethal substances than toxic waste flooded through many of them. Drainage channels diverted much of the water into specially constructed flood chambers and the natural dryness of the soil absorbed a great deal of moisture. The tunnel would survive, but there would need to be additional props installed to keep it from subsequently collapsing. Such work would need to be carried out by the Iron Warriors, since these toxins would remain lethal for many hundreds of years. But to warriors in power armour, they were irrelevant.
Forrix shook his helmet clear of thick sludgy deposits and waded back through the waste-filled darkness to the main tunnel, knowing what must happen next. Bones crunched beneath his heavy tread as he stepped on drowned corpses. The toxic waste was draining rapidly. As he made his way back to the rockface he checked the action of the bolter, clearing it of obstructions.
Up ahead he could see beams of light stabbing down into the cavern from the hole in the roof and heard the first splash of something heavy drop from above. The darkness of the tunnel was no impairment to Forrix, and he saw an Imperial Fist rise to his feet. The Space Marine moved swiftly through the knee-deep sludge towards the tunnel mouth.
Forrix shot him in the head as more Imperial Fists dropped to the cavern floor, spreading out as the echo of his shot faded. Bullets hammered the rock around him and ricocheted from his armour. He raised the bolter and swept its fire around the cavern, gunning down Space Marines as he backed into the relative safety of the tunnel where the enemy could not bring their superior numbers to bear. If they wanted to kill him, they were going to have to come and dig him out.
Shapes darted across the opening and he fired at each one as it presented itself. Forrix laughed as he killed, spraying the tunnel mouth with bolter fire. Muzzle flashes lit up the Stygian darkness as gunfire blasted from the walls of the tunnel. He felt sharp pain in his side and shoulder as more bolts impacted on his armour. As mighty as Terminator armour was, it could still be brought down by sheer volume of fire.
The bolter he carried clicked empty and he dropped it into the effluent, reactivating his power fist as two Imperial Fists rushed him. He killed the first with a mighty punch to the head, and the second with a reverse stroke that tore out his throat.
Another two warriors charged. Forrix roared in battle fury as he felt the blade of a crackling sword rip through his armour, between his ribs and into his primary heart. Angrily he slammed his fist down across the blade, wrenching it from the Space Marine's grip before removing his arm with a backhanded blow. He shoulder charged the other warrior, crushing his helmet against the tunnel wall before disembowelling the armed Space Marine with his power fist.
Gunfire hammered him and he felt the bone shield within his chest cavity crack as a bolter shell exploded within the ceramite plates of his armour. He dropped to his knees as the Imperial Fist closed the gap, firing as he advanced. Forrix tore out the sword protruding from his chest and hacked the warrior's legs out from under him, pitching him face-first into the waste matter.