Images of men with cut throats flickered through my mind. Maybe they had taken out the sentries with it, paralysed some of the men, but there was more to it than that. All of the corpses I could see were wearing rebreathers. Not that it mattered much. There had been dozens of consignments of faulty masks sent to the front. Some said it was simply the usual incompetence of the Imperial manufactorums. Other claimed corners were being cut to fatten the profits of the merchant houses. I had heard Macharius rail against such things often enough not to dismiss the possibility.

Rebreathers, I thought. It niggled at my mind. I knew I was missing something but I could not work out what. I moved along the duckboards over the sewage trench. I thought about all of those naïve newcomers who never checked the filters on their masks, who trusted that they would work and who died, their lungs filling with froth, during the first gas attacks. I had tried lecturing them. I had tried setting an example. I had tried many things, but some people always know it’s not their problem, that death always comes for somebody else, until that final moment when they realise that they are not immortal after all.

I looked down at the latrine trench and saw the brown mix of excrement, urine and mud. I noticed the faint swirls in it that were not caused by the rain and then I knew…

A bump emerged from the muddy mess. I blinked. It took a heartbeat for my brain to process what I was seeing. Something erupted out of the latrine trench. Instinctively I pulled the trigger on the shotgun and the thing came apart. The impact of the shot revealed the red of blood, the pink of flesh and the white of bone. The torn form of a heretic soldier flipped backwards into the mess.

I heard shouts from behind me as surprised soldiers responded more slowly than I had. The enemy assault squad had been waiting below the surface of the latrine trench, breathing through snorkels, examining us through periscopes. Those had been the strange pipes I had noticed at first.

Along the line horrified Imperial Guard soldiers were engaged in close combat with foes who dripped a trail of slime behind them and gurgled a name that sounded like Nurg-Al from deep within their chests. There was an awful suggestiveness about the name. Hearing it made the hairs rise along the back of my neck, and I felt an ominous sense of foreboding that made me want to stop the chanting any way I could.

The attackers were well trained, had the element of surprise and inspired horror and revulsion, but my men were holding their own. They were members of Macharius’s elite guard, after all. They might even have been able to turn the tables on their attackers by the fury of their counter-assault had not more heretics erupted from the bunkers behind us, thrusting with blades, firing autoguns. An attack from two sides was almost enough to erode the courage of any warrior. There is nothing like the sensation that you might be stabbed in the back to get you looking over your shoulder, fighting with less than your customary efficiency and making you think about running for it.

I pumped the shotgun and twisted at the waist.