Further up, the curved walls were hung with banners, rust-red cloth embroidered with binary prayers in gold thread. The brightness gave way to shadows towards the ceiling, incense-stained darkness swallowing the cathedral's light where Thaddeus could just make out the control structures looking down on the cathedral, where tech-priests might even now be watching intruders violating the Omnissiah's temple.

The technology of this place was the old kind, the kind they couldn't make any more, salvaged from the forgotten madness of the Dark Age of Technology and put to a new use in the worship of the Omnissiah. This was a sacred place indeed, where the Adeptus Mechanicus kept technology they could not - some said would not - replicate.

To Thaddeus, it was beautiful. To Lieutenant Kin-darek and his men it was just another warzone. Kindarek barked an order and the platoons fanned out behind the pointmen, who were rapidly scanning the ridges of the metal sandbar. The platoon dissolved into its component squads, each overlapping fields of fire.

'What's our entry point, sir?' came Kindarek's voice.

Thaddeus glanced around. They couldn't spend more than a few moments down here, where they had no cover and where gunfire could make the hydrogen lake erupt. There were several maintenance stairwells hanging down from the columns above, where adepts or servitors could descend to the lake surface. Thaddeus pointed towards the closest. 'There. Keep it simple.'

'Sir.’ At Kindarek's order the platoon jogged towards the stairwell, a spindly spiral of pale silver metal that seemed impossibly fragile against the sheer size of the cathedral cylinder.

The pointmen ascended rapidly, taking two of the grenade launcher troopers with them. The squads went up after them, Thaddeus jogging alongside them as they took the stairs two at a time in their hurry to get out of such a vulnerable position. Thaddeus glanced down and saw the rear of the shuttle disappearing from view as it slid back under the surface to minimise the chances of detection.

The webs of light above fractured and reformed as Thaddeus ascended, as if the whole cathedral had been constructed to appear radically different from each possible angle, mirroring the billions of facets of information it contained. He almost stumbled as he stared up at the sight and remembered that he was a soldier, too, just like these men who were ignoring the splendour, their minds only on the mission.

The pointmen were at the first level of the weblike walkways, picking their way warily along the transparent crystal. The base of one of the suspended columns was nearby and they gathered there, one consulting an auspex to check for movement, others checking cautiously around the giant smooth pillar.

Kindarek waved the first of the platoon's squads onto the walkways. They spread out into a mobile perimeter, hellguns ready to fire, moving around the abstract geometric shapes that formed the crystalline information vaults.

Several men carried bundles of equipment slung at their waists or backs - basic interface equipment, guaranteed to survive the intense cold, that would enable the user to jack into a simple information system. Many of the more technically-minded storm troopers had been quickly trained in its use, and Thaddeus himself could perform the vital task if need be.

Kindarek himself had got to the walkways. For a moment he paused and looked towards the troopers by the pillar - Thaddeus saw one of them, one of the pointmen with an auspex, mouth a single word as he voxed the lieutenant.

Movement.

That was all the warning Thaddeus had.

The trooper turned as he tried to gauge the source of the movement signal on his auspex scanner. He faced the pillar behind him and dropped the scanner to bring his hellgun to bear as he realised the movement was inside the pillar.

The pillar's surface fractured into hundreds of dark grey ceramic tiles. The column broke apart and the tiles were revealed as the flexible armoured carapaces of giant metal-limbed beetles that hung in the freezing air as a host of glowing metal eyes lit up on the scanner arrays jutting from their thoraxes.

The lower half of the pillar had broken into more than twenty combat servitors, each three times the bulk of a man, highly advanced and hovering with in-built grav-units. Metallic limbs folded into mul-tilaser barrels and circular diamond-toothed power saws emerged on metallic armatures. In the few seconds before the servitors were battle-ready Thaddeus realised they had indeed been observed as soon as they had made it to the shore - the cathedral's defences had waited until the storm troopers were spread out between the walkways and the stairwell, vulnerable and out of formation.

Stupid. How could Thaddeus have believed he could succeed in infiltrating the Pharos archives when it had been proved impossible so many times?

No. That was the thinking of someone without faith. Fight on, for death in service of the Emperor was its own reward.

'Open fire!' yelled Kindarek over the squad vox. 'Launchers, now!'

The frozen air erupted into laser fire, searing red streaks from the overcharged power packs of the hellguns lashing from every trooper able to shoot, multi-lasers pumping volleys of white fire through the bodies of the troopers closest to the pillar. The screech and hiss of laser fire filled Thaddeus's ears and the vox was suddenly a mess of static and din, men shouting as they opened fire or screaming as they died. Men were shredded, their blood freezing into a hail of red shrapnel, chunks of flesh shattering against the crystal. One fell backwards as his leg was sheared clean off by the slash of a power saw, beads of frozen blood glittering as he tumbled off the walkway down towards the hydrogen lake. Another was picked up by the razor-sharp mandibles of the beetle-servitor and pulled apart, his body erupting in a shower of crimson shards.

White-hot laser fire slashed through the stairwell and the man directly above Thaddeus was hit, his torso shattering as a laser bolt punched through his chest. White fire screeched through the stairs beneath him and the structure came apart, metal steps raining down along with half of the last squad.

Thaddeus reached out and grabbed the railing as the steps under his feet disappeared. The bulk of the . dead man above buffeted him as it fell, and Thaddeus was dangling one-handed nearly a hundred metres above the lake. The blinding light swallowed the men as they fell, reducing them to ripples in the silvery surface as they hit the lake.

Grenade rounds exploded above, sending clouds of shrapnel ripping through the servitors. The damage was minimal but the explosions scrambled their sensors, and one of the insectoid servitors fell wreathed in strange blue flame as a dozen high-powered hellgun shots tore up into its underbelly.

'Paniss! Telleryev! Make for their flank, pin them down!' Kindarek was yelling - Thaddeus saw Kindarek, back against one of the information-sculptures, firing with his hellpistol as he shouted orders over the vox.

A hand reached down and Thaddeus grabbed it -a trooper hauled him up onto the still-stable top end of the stairwell. Thaddeus was about to breathe a word of thanks when a laser shot seared through the air between them and sliced a deep furrow through the trooper's faceplate - Thaddeus saw him choke as the cold air he inhaled turned his lungs to chunks of ice. The man's eyes froze into white crystals and his body turned rigid, the heat fleeing from inside his suit and his muscles turning solid.

Thaddeus pushed the dead man to one side and let the corpse fall. He stumbled forward a few steps and pulled himself onto the walkway, the dizzying drop still yawning beneath him. The passage was only wide enough for a couple of men abreast and troopers were scrambling for the junctions where they could gather in gaggles of three or four, using sculptures as cover and concentrating hellgun fire on one servitor at a time.