Eventually they reached the rockcrete apron surrounding the bunker and slammed into its reassuringly solid bulk. As more lightning burst overhead, tyranid creatures slid downhill from the slopes above, skidding in the mud as they tried to find their footing. Silhouetted in the glare, Uriel saw the carnifex and the monstrous winged beast finally crest the plateau and lumber towards the bunker.

'Everybody inside, now!' yelled Bannon, firing at the carnifex as he limped backwards. Uriel stood beside him, loading and firing off another magazine to little effect. The monster's screeching roar echoed from the mountains as it charged through the rain. Uriel ducked inside the bunker grabbing the giant locking wheel and shouting, 'Bannon! Get inside, now!'

The Deathwatch captain kept firing and Uriel was about to repeat his order, when Bannon turned and ran inside, dropping his bolter and helping Uriel with the door. Armoured and sheathed in double layers of adamantium, the door weighed over four tonnes, and was normally closed by means of hydraulic pistons, but Uriel and Bannon pulled it shut in seconds, desperation lending their limbs extra strength.

The door slammed closed and Uriel spun the locking wheel.

'That was too close,' breathed Uriel.

'Aye,' agreed Bannon, scooping up his weapon.

The steel of the door buckled inwards with a resounding clang. Thunderous impacts rocked it and dust fell from the ceiling. Glow-globes on the ceiling flickered with each impact.

'Come on,' said Bannon, 'This door will not hold them for long,' and marched along the bare rockcrete corridor. Casting wary glances at the booming door, Uriel followed him, eventually arriving in the humid fire-control chamber. Banks of ancient technology lined the edge of the octagonal room and an iron ladder led up to a brass rimmed hatch in the ceiling.

Magos Gossin sat before what was presumably the main firing panel with his head bowed in prayer, his tech-priests kneeling behind him and chanting in counterpoint to their master's words. Mud-caked Deathwatch Space Marines stood at attention as the droning mantra continued, with no sign of drawing to a close.

'Magos Gossin,' snapped Bannon. 'When can you fire these guns?'

Gossin turned in his seat, his displeasure at having been interrupted plain. 'The capacitors are linked to the main grid, but the necessary prayers to begin the firing sequence are lengthy and intricate. It would be preferable if you did not interrupt me as I perform them.'

Bannon marched towards Gossin as another impact slammed into the main door.

'Do you hear that?' he demanded. 'We have minutes at best before the tyranids are upon us. Fire these guns now or they will not fire at all. Do you understand me?'

A tortured metallic screech echoed through the bunker. Gossin stared fearfully along the corridor and nodded.

'Deathwatch, with me!' shouted Bannon, heading back towards the door.

The viewing bay of the Vae Victus lit up with the destruction of the Kharloss Vincennes, reflected light from the explosion flaring from the glossy carapaces of the tyranid bio-ships.

'Emperor watch over thee,' whispered Tiberius as another impact rocked his vessel. Deathly red light bathed the command bridge as more and more tyranid weapons scored hits. Their defensive capabilities had been degraded comprehensively by hundreds of drifting spores and there was nothing he could do to stop it.

The Sword of Retribution still fought, her captain performing brilliantly in evading the tyranid creatures and hammering the hive ship's escorts.

'He's fighting to reach the second hive ship,' said Philotas.

But Tiberius could see he wouldn't make it. Already organisms were swarming over her hull and suffocating her firepower.

They had come so close! The first hive ship was right in front of them. The Vae Victus and the Mortis Probati had stripped away a huge portion of its defences, diverting much of the defences previously protecting it from attack from the planet's surface.

But there was no attack from the planet and Tiberius felt his heart sink at the thought that they had failed.

'All ships, prepare to disengage,' he said.

The door blew inwards, ripped in two by a massive pair of claws. Rain and wind howled inside the bunker as a dozen hormagaunts fought to squeeze past the screaming carnifex that smashed its claws into the rockcrete around the door in fn attempt to squeeze its massive bulk inside. A volley of disciplined bolter fire brought down the first and second waves.

A giant crack split the ceiling, the carnifex bludgeoning its way forwards.

Screeching howls and deafening blasts of gunfire filled the narrow corridor.

Uriel aimed at the carnifex's head, its blunt features expressionless as it hammered its way inside. His shot put out its eye, blasting a chunk of skull clear. The beast flinched, but simply lowered its bony head and slammed harder on the bunker's structure.

Leaping hormagaunts filled the corridor, screeching with alien fury as the Space Marines slowly fell back before them. Glow-globes shattered and the ceiling split apart with a booming crack. Huge chunks of rock dropped into the corridor. Uriel hurled himself clear as tonnes of rock collapsed and billowing clouds of dust filled the air.

He dragged himself to his feet, scrabbling for his fallen bolter as a mud-covered warrior organism leapt atop the steel-laced rubble. Its fangs spread wide and a secondary set of jaws lashed out, biting deep into Uriel's helm. His visor shattered and he felt blood on his face as the jaws withdrew. He dropped to his knees against the wall, disengaging the vacuum sockets on his gorget and tearing the helmet loose.

The tyranid warrior pounced and a hail of bolter shells stitched across its thorax, exploding wetly within and spraying Uriel with its blood. Bannon hauled him to his feet as the tyranids clambered over the rubble and the Deathwatch hammered them with more shells.

Without the protection of his helmet's auto-senses, the noise was deafening. Gunfire and thunder combined with the lightning to form a cacophonous backdrop to the battle. Dimly Uriel heard Bannon calling the Thunderhawk down as they fell back towards the control chamber.

As the Space Marines withdrew, Uriel was suddenly aware of a bitter, metallic taste on the air as a powerful static charge built around him. His scalp tingled and even over the noise of battle he could hear a deep, bass thrumming build beneath him.

He looked up through the shattered ceiling in time to see an incandescent streak of light spear skywards, looking like the manifest wrath of the Emperor

Once again the viewing bay lit up, and it took Tiberius a moment to realise why. Another streak of light slashed past the Vae Victus blasting clean through the body of the hive ship. Another shot fired, followed closely by another and he surged from his command pulpit and punched the air.

'Damn you, Uriel. I knew you could do it!' he yelled over the ringing of alarm bells.

With atmospheric conditions more or less stable in the region selected by Uriel and Sebastien Montante, the beams from the defence laser silo were unaffected by the thermal blooming that had so hamstrung the defences in the opening stages of the invasion.

In low orbit, and with its planetward defences engaged in protecting it from the Imperial fleet, the hive ship was horribly vulnerable and was now paying the price. Explosions of flesh rippled across the hive ship's body as blasts from the defence lasers destroyed it.

'All ships, belay my last order!' he shouted. 'Target everything you can at that hive ship! We've got it, by the Emperor, we've got it!'