His vision cleared in time for him to see Ikrek’s head vanish. Ceramite and bone shards rang on Saduran’s armour.

The chug-boom of heavy cannons. The double thud of his heartbeats rising.

A round hit Ikrek’s corpse as it fell.

Saduran ducked left. His bolter was in his hand.

A round hit the legionary behind him. The warrior gasped as he crumpled.

Target runes flashed red across Saduran’s sight. He fired.

They were in a vaulted junction between three wide corridors. Air was rushing out of the edges of the breach punched by the assault ram through the exterior wall. Blast doors were already dropping across the mouths of the corridors. The automated cannon had dropped from a hatch in the roof. Machine-slaved and shielded with ceramite plates, it was pouring shells down onto Saduran and his squad without pause.

‘Breach the doors!’ shouted Saduran as he fired up at the cannon again. Explosions flashed off its armour plates. Shrapnel scattered from it. Micro-shards pinged from Saduran’s helmet like hail. The cannon barrel twitched around to track him.

Four of his squad mates ran towards the closing doors. The cannon barrel swung away from Saduran and put wide holes through two of them. Saduran saw the gleam of a targeting lens nestled next to the cannon’s barrel. He put a burst of three rounds into it. The cannon spun, firing blind, shells punching into the deck and walls.

There were no troops yet, but they would come. This was one of the star forts that guarded the approaches to Pluto and the volumes around the Khthonic Gate. Like all the rest it was the size of a battle cruiser, a behemoth of stone and metal three kilometres across, studded with batteries and void shield generators. It took a battle group to kill each one, and ships would be lost doing it. There were ships to spare, though, hundreds of them, and if taken, this star fort could protect a corridor towards Pluto’s fortress-moons. Ships could pour through that opening. So, a battalion of newborn Sons of Horus had been unleashed to take the star fort by blade and blood. It was like driving a wedge into a stone sphere – drive deep enough and the sphere would crack, then shatter.

Two of Saduran’s squad-brothers reached one of the closing blast doors. They pulled melta charges from their backs, swung them into the ever-narrowing opening at the bottom of the doorway and leapt aside. The charges armed an instant before the descending door met them. Spheres of blinding light screamed into being. The lower section of the door collapsed in a wash of molten metal. Saduran was already running at the breach.

A pressure wave almost knocked him off his feet as a second assault ram punched through the fortress’ skin. He kept moving forwards.