The squad rapid-fired as they ran, spattering bolter fire into the defences. Blue-armoured eldar, seeing this new threat landing behind them, turned to man the defences they had just overrun. Their shuriken guns spat volleys of shining silver at Korvax and his squad, studding the Soul Drinkers' purple armour with razor-sharp discs. One Marine - Solus, the squad's flamer-bearer - went down, crimson spurting from the disk embedded in his knee joint. The bolter and shuriken fire met in a storm of metal, the Soul Drinkers closing quickly as the other squads did the same along that whole side of the defences.

The night sky above was clear and cold, and through it streaked a missile from Squad Veiyal, cracking in a flash of fire into the centre of the eldar sword-bearers. Two of them died, blown apart. Bolter fire ripped into them as they tried to regroup, and by the time Squad Veiyal reached the defences the xenos manning it were dead.

Korvax's squad hit the eldar on their section of the line. Korvax tore up the edge of the sandbag parapet with full-auto fire and deftly drew the power sword from its scabbard on his armour's backpack. The power field jumped into life as his gauntlet closed around the hilt and it shrieked as he brought it down towards the first eldar he saw. Eldar reflexes were notoriously quick and the alien jinked to the side, but the blade still caught its shoulder and sheared the arm clear off. Korvax vaulted into the ditch behind the parapet, kicking the eldar to the floor as he did so and bringing his bolter, like a club, cracking into the side of its skull.

Bolter fire spattered like rain into the ditch. Eldar died, or stopped firing to scramble out of the way. The ditch was deep but the far edge had collapsed into a crumbling slope where the frozen earth had been pulverised by explosive fire - the eldar retreated up this, attempting to fire as they went.

One of them moved with sudden, supernatural speed, seeming to flip over trails of bolter fire. It had a sword that looked like it was made of bone in one hand and a shuriken pistol in the other - the pistol flashed and a shuriken took Brother Brisias through the eye.

Korvax crunched through the body of the eldar he had killed and drove up the slope towards the eldar with the sword - part of their leadership caste, he guessed. They said eldar followed many paths of war, each type of soldier the result of a different path - those who became trapped on those paths became their leaders on the battlefield. They were considered priority targets in assaults.

The eldar saw Korvax approach, and fixed the black glass of its helmet eyepieces on him for a moment. As if acting on some warrior code, the alien paused for a split second, raised its blade, and somersaulted towards him.

Korvax followed no code save that of the Emperor and the sacred place of the Soul Drinkers in his plan for the Imperium. In the shadow of the beleaguered outpost he duelled with the eldar leader, matching the alien's speed with his own strength. Many times the eldar struck home with a blow that would have killed a normal man, but Korvax knew the protection that power armour offered and he knocked each blow aside with a shoulder pad or an armoured forearm.

The alien tried to flip away from him, but Korvax reached out with his free hand, grasped the plume of its helmet, pulled its head down and slammed his knee into its faceplate. The eldar reeled and Korvax slashed a deep gouge across its torso, cutting through the armour plates set into its deep blue bodysuit. He felt its thin ribs give way and drove forward, hacking at it as each parry from its bone sword became weaker. With one final slash Korvax brought the blade down through the eldar's guard and the power blade cut right through the alien's torso, shearing the spine. The alien froze for a moment, then fell limp. The sword dropped from its hand.

The power field around the blade burned away the tissue it touched and the corpse slid off the sword with a flick of Korvax's wrist. The blue-armoured eldar were dead. The Soul Drinkers had taken the aliens by surprise, catching them as they themselves were trying to storm the outpost with speed and skill. Korvax saw Squad Veiyal was almost at the outpost's front blast doors - he also saw that the doors were wide open and smoking. The xenos must have got inside.

The Adeptus Mechanicus Biologis outpost was a crucial research station. The experiments it housed were vital to the Imperium. Korvax did not know the exact nature of the work done here, but for the Adeptus Terra to ask the Soul Drinkers to defend it from alien raiders must mean that the work was of the greatest importance. If the eldar got inside and destroyed - or, worse, stole -the Mechanicus research, the consequences would be great.

They were too late. The heathen xenos had breached the outpost. It was time to make amends.

Korvax quickly voxed round his squads. Veiyal was the furthest forward while two other squads were busy pinning down the eldar reinforcements landing nearby. Assault Squad Livris was on Korvax's flank, clashing chainswords with the green-armoured eldar. They had lost a couple of Marines but they had cut their way through most of the eldar. That left Korvax three squads for the assault, with two more keeping the emerging eldar support units at bay.

"Veiyal, Livris, rush the doors!' voxed Korvax on the all-squads channel and he waved his squad forward, the Tactical Marines firing volleys sweeping across the defences in front of them as they advanced. More blue-armoured eldar tried to dig in and hold off Kor-vax's squad, but he led his men charging into their flank and drove them against Squad Livris. Many more eldar died between Korvax's bolter fire and Livris 5 chainswords.

That was how the Soul Drinkers fought. Hard and fast, never stopping.

Korvax saw Squad Veiyal at the doors, using the massive plasteel construction of the blast doors as a firepoint, as they gave covering fire to the two squads approaching. Explosive fire suddenly streaked over from the eldar heavy weapons units trying to reach the outpost. Bursts of fire and shattered earth fountained up where they hit, and several Marines were thrown off their feet. The autosenses of Korvax's helmet cut out for a second then juddered back. A warning icon flashing on his retina told Korvax the pict-recorder on his backpack was damaged, and was no longer recording the view over his shoulder for the mission's debriefing.

Korvax would have to survive. He ran on through the pall of falling earth as a rune winked out, indicating Brother Severian's lifesigns had ceased in the midst of the barrage. Korvas ducked into the doorway and his squad barrelled in behind him. Blue-armoured eldar fired shuriken shots after them but were shredded by Livris's charge, and the Assault Marines joined the rest of the spearhead at the outpost entrance.

Korvax checked the runes on his retina display. There were about half a dozen Marines down, maybe dead, but definitely out of action. Not bad losses. But the eldar had got inside the outpost and could even now be wrecking research vital to the Imperium.

Korvax slammed a new magazine into his bolter and heard half his squad doing the same. He glanced at Sergeant Veiyal - his helmet had been damaged and he was bareheaded, his breath coiling white in the cold.

'The others have our backs,' said Korvax. 'Sergeant Livris, your squad has the point. Veiyal, with me. Advance!

Korvas levelled his bolter and followed the Assault Marines as they charged into the darkened heart of the outpost...

THE IMAGE WINKED out to be replaced by static. Thaddeus frowned and tapped the controls on the data-slate, rewinding the recording past the point where the feed cut out. It was the view over the Space Marine commander's shoulder from a recorder on his backpack, showing a screen full of showering earth and sharp white lines of gunfire. The recording rewound and the Soul Drinker commander's charge played out in reverse. Implosions sucked Marines back onto their feet.