‘And what if your ship has already been found?’ I asked, following my brother and his warriors as they waded into the murky sewer. It was dark in the tunnel, only illuminated by the fizzing glow of phosphor lamps.

‘Unlikely,’ Corax answered. ‘It is masked beyond the means of this vessel’s sensorium to detect. Come on.’ His warriors were ranging ahead, and I soon lost them in the gloom.

We tramped on through the filth in silence, the disturbed waters only making the fumes more noisome. As above, below it was a labyrinth and I had the distinct feeling we were heading down towards its core. A part of me yearned to find Curze waiting there, so I could inflict upon him every act of retribution I had dreamed about since being incarcerated at my mad brother’s pleasure.

It would be so easy… His skull in my hands, the bone cracking as I slowly crushed it.

The long stretch of straight bilge pipe was finally giving way to a sharp bend when I caught the stark muzzle flash in my eye line and heard the grunted accusation of discovery.

Corax was already moving, several metres ahead of me, power whip cracking in his gauntleted fist. ‘They have found us!’

I heard one of the Raven Guard fall, but didn’t see it. Our vanguard was beyond the bend; so, too, was Corax now, and I could only hear the battle. There was a loud splash and I assumed that the warrior had sunk into the water.

I reached the turn but found only darkness in front of me. Even with the phosphor lamps, spitting and flickering in the rank air, I could see neither friend nor foe.

Another flash set me to purpose, a fleeting pict-capture of monochrome grey lodged in my retina of two legionaries clashing with blades. I roamed towards them, finding sludge under my feet and progress slow. The next section of pipe was equally as long as the first and my allies fought some way down it, far from my aid.

I stopped, trying to ascertain how many enemies we were facing, and where. Without the muzzle flash my sight was hindered again. I set the bolter I had been given under my chin, resting the stock against my cheek as I slowly panned it around the sewer. Weapons fire reverberated off the vaulted ceiling, echoing loudly, making it difficult to pinpoint. I realised the pipe in this part of the sewer was far from straight. Columns supported it, their foundations beneath the rancid waterline. There were alcoves and sub-ducts, maintenance ledges and antechambers. Without a bearing I could quickly lose my way, and my rescuers with it.

Somewhere in the distance, Corax was fighting. I heard the crack of his power whip, and could smell the ozone reek of his lightning claws even above the rancid fluid slowly riming my waist. I broke through the viscous skin that had started to encircle me, wading quickly through the morass as I fought to reach my brother.

In shuddering silhouette I saw another Raven die, his wings bent outwards as a bolt shell tore him open.

‘Corax!’ I called out, still panning with my bolter, concerned that any snap shot might hit my brother or one of his sons.

I heard the clash of steel, a burst of bolter fire, but got no answer.

‘Corax!’

Still nothing. The tunnel yawned in front of me, a diseased and gaping maw, and the darkness closed like a storm. I caught flashes, muzzle fire and the ephemeral flare of power weapons. Nothing more than silhouettes greeted me, the after-image of a blow already struck, a kill already made.

In the foulness sloshing around my waist, I caught a brief sight of an armoured corpse. In the dark, face down, it was hard to discern who it belonged to. I forced my way over to it through the mire, but was too slow. Trapped air escaping from the gaps in its armour, the corpse sank without trace. I plunged my hand into the filth, reaching and grabbing for it. I needed to see it, to touch something undeniably real. Something scraped against the tips of my fingers. Delving deeper, the rank waters lapping at my face, I grasped the object. Bringing it up into the light, I saw a skull. Sewer-filth peeled off bleached bone like a sloughing skin. It grinned, as all skulls do, but I found some familiarity in its macabre visage.

Ferrus Manus’s cleaved head stared up at me.

Recoiling, I dropped the skull and was about to reach back down for it when I heard Corax shout out.

‘Vulkan!’

A small spherical object, its activation stud flashing, arced overhead. Its parabola took it down into the waters, almost on me.

I turned, taking a sharp breath and closing my eyes as a concussive blast pushed me down into the mire. Skin stinging with the host of shrapnel embedded in my back, I touched the floor of the tunnel, my head and shoulders completely submerged. The spike of a rib, a jutting femur, the ridged line of a spinal column – I scratched at the underwater boneyard in a desperate attempt to gain purchase and rise above the water.

Then I was rising, carried along in the sudden swell caused by the explosion, before breaching the surface. Thrown into the air, chased by a gush of filth, tendrils of it clinging to my body, I hit the wall hard and slid down against it.

I had lost my bolter, the weapon slipping from my grip during the fall. Gagging, coughing up filthy water from my lungs, I heard approaching footsteps splash through the mire.

Dazed, my vision blurring, I looked up and saw a hand proffered towards me.

‘It’s over,’ said Corax.

‘I didn’t even see them,’ I gasped.

‘Trust me, brother, they’re dead, but more will be coming after that explosion. We have to move.’

With Corax’s help, I got to my feet and together we reached the end of the sewer tunnel, where a maintenance ladder led up and out.

‘Where are the others?’ I asked, not seeing Kravex or any of the other Raven Guard.

‘Dead,’ Corax replied grimly, and kept his eyes front. ‘Here,’ he said, gesturing to the ladder. ‘I’ll go first. Follow me closely.’

I nodded and tried not to think about what my brother was feeling at that moment.

Halfway up the ladder, Corax said, ‘They knew the nature of this mission, and accepted its risks.’

I didn’t reply, merely followed in silence.

Though thick with fumes emanating from the enginarium decks, the air beyond the sewer was almost cleansing by comparison.

Another large chamber stretched out before us. It was cluttered with machinery and packing crates. Cranes loomed overhead and a gantry overlooked the space on one side. It appeared to be empty.

‘Ancillary deck,’ Corax explained, breaking into a steady run, ‘mainly used for storage and repairs. Relatively small. Difficult to breach.’

‘Your ship is close?’ I asked, keeping pace.

‘This way…’

Corax reached the junction first. As he stopped dead, I knew something was wrong. When I caught up to him, I realised what.

Pressure vented from a tear in the Thunderhawk’s fuselage. A jagged hole punched inwards, scorched marks radiating from the breach. It was still seized in its locking clamps, though one of its stanchions was twisted. The glacis plate in the nose cone was shattered, its prow-mounted guns wrecked.

‘Looks like your flight will have to be aborted,’ a low voice declared from the shadows.

The lumen strips overhead were extinguished with the sharp thunkof a thrown switch.

Darkness prevailed for a few moments until twin ovals of crimson light from a warrior’s retinal lenses pierced the gloom. He was joined by twenty more, fanning out from alcoves and behind the scuttled gunship where they had been lying in wait, assembling in front of us to block off the deck.

Corax and I stood our ground.

‘So few of them…’ he remarked to me.

Ten more legionaries clanked into position behind us.

‘So very few,’ I agreed.

A warrior in Terminator armour, one of the Atramentar, stepped forwards. ‘Lay down your arms.’