‘Salamanders,’ roared Dak’ir, rallying his squad as he pulverised the cultist’s face with an armoured fist. He took up his chainsword, which had spilled from his grip in the blast, eviscerating three more insurgents as they came at him with cudgels and blades.

Reaching for his plasma pistol, he stopped short. The atmospheric readings in his battle-helm were showing a massive concentration of hydrogen; the air inside the dome was saturated with it.

To Dak’ir’s left flank, Ba’ken was levelling his heavy flamer as a massive surge of cultists spilled into the hall…

‘Wai–’

‘Cleanse and burn!’

As soon as the incendiary hit the air, the weapon exploded. Ba’ken was engulfed in white fire then smashed sideways, through the rockcrete wall and into an adjoining chamber where he lay unmoving.

‘Brother down!’ bellowed Dak’ir, Emek offering suppressing fire with his bolter as he came forwards, chewing up cultists like meat sacks.

More were piling through in a steady stream, seemingly unaffected by the bolt storm. Picks and blades gave way to heavy stubbers and auto-cannons, and Dak’ir saw the first wave for what it was: a flesh shield.

Another Salamander came up on the sergeant’s other flank, Brother Ak’sor. He was readying his flamer when Dak’ir shouted into the comm-feed.

‘Stow all flamers and meltas. The air is thick with a gaseous hydrogen amalgam. Bolters and secondary weapons only.’

The Salamanders obeyed at once.

The press of cultists came on thickly now, small-arms fire whickering from their ranks as the heavy weapons were prepared to shoot. Dak’ir severed the head from one insurgent and punched through the sternum of another.

‘Hold them,’ he snapped, withdrawing a bloody fist.

Ak’sor had pulled out a bolt pistol. Bullets pattered against his armour as he let rip, chewing up a bunch of cultists with autoguns. The dull thump-thud of the heavier cannons starting up filled the room and Ak’sor staggered as multiple rounds struck him. From somewhere in the melee, a gas-propelled grenade whined and Ak’sor disappeared behind exploding shrapnel. When the smoke had cleared, the Salamander was down.

‘Retreat to the lobby, all Salamanders,’ shouted Dak’ir, solid shot rebounding off his armour as he hacked down another cultist that came within his death arc.

The Astartes fell back as one, two battle-brothers coming forward to drag Ba’ken and Ak’sor from the battle. As Dak’ir’s squad reached the stairs and started to climb down, Sergeant Lok rushed in. Due to the presence of the explosive hydrogen gas the Incinerators were down to a single heavy bolter, strafing the doorway and ripping up cultists with a punishing salvo.

There was scant respite as the enemy pressed its advantage, wired-mouthed maniacs hurling themselves into the furious bolter fire in their droves. Brother Ionnes was chewing through the belt feed of his heavy bolter with abandon, his fellow Salamanders adding their own weapons to the barrage, but the cultists came on still. Like automatons, they refused to yield to panic, the fates of their shattered brethren failing to stall, let alone rout them.