Electrical fires and gouts of poisonous flame, chittering devourer creatures and bony shrapnel bombs pounded the walls relentlessly and as casualties spiralled into the tens of thousands, the decision was made to abandon the first wall.

Barely anything remained of its parapet and the smaller creatures had entered another evolutionary iteration, spontaneously developing fleshy tendons equipped with jagged hooks that enabled them to scale the sheer surfaces of the walls. The many guns mounted on the sides of the valley were keeping the majority of the aerial creatures at bay, and after the ambush at the city wall, no one was dismissing the possibility of the tyranids attacking from avenues previously considered impossible.

Pockets of aliens had penetrated the city through drainage culverts, forgotten caves and even over the high peaks of the mountains, and, while they were wreaking havoc among the civilian population, not a single man from the front line could be spared to hunt them down.

For now, the people of Erebus would need to look to their own defence.

Uriel felt the cold against his skin as a burning sensation, but welcomed the pain as a sign he was still alive. His armour was dented, torn and gashed in innumerable places, stained with so much alien blood that its original colour was scarcely visible. The actuators in his left shoulder guard wheezed as he walked, the result of the none-too-tender ministrations of a gigantic tyranid warrior organism. Techmarine Harkus had done what he could to allow the auto-reactive shoulder guard to move freely, but without the proper blessed instruments, he had been forced to beg the armour's forgiveness and effect a temporary repair.

He had not slept since the destruction of Colonel Rabelaq's Capitol Imperialis, and while his catalepsean node had allowed him to continue to function, influencing the circadian rhythms of his brain and his response to sleep deprivation, he felt a marrow-deep tiredness saturate his body.

Looking at the thousands of men gathered around the lines of flaming braziers he felt his respect for them soar. If he was this tired, he could not imagine what the human soldiers must be feeling. Learchus, his armour similarly brutalised, looked well rested, his eyes bright and his stride sure as he marched beside his captain.

'Guilliman's oath, these men are weary,' said Uriel.

'Aye,' agreed Learchus. 'That they are, but they'll hold. I know they will.'

'You trained them well, brother-sergeant.'

'As well as the codex demands,' said Learchus, a hint of reproach in his tone.

Uriel ignored his sergeant's gentle rebuke as they emerged from the buildings of District Quatros and onto the rained plain before the second wall.

Where once the area had been thronged with factories, production hangars and dwellings, there was now only iced rockcrete rectangles to indicate where they had once stood. Lines of burning oil drums packed with whatever flammable materials were to hand burned and kept the air just above freezing. Already scores of soldiers had perished in the cold nights, frozen to death where they lay, their comrades forced to pry their corpses from the ground as dawn broke.

The council of Erebus, initially supporting Learchus's decision to demolish the buildings so as to deny the tyranids cover between the walls had balked as the reality of the proposition had hit home. Simon van Gelder led the most vocal group of opposition and, in a move of surprising boldness, Sebastien Montante had dissolved the council of Erebus, giving command of his city to Colonel Stagler until such time as the tyranids were driven off.

It amazed Uriel to think that on the brink of annihilation, men could still squabble over such petty concerns as property and wealth. This world might bear the name of the Ultramarines, but its leaders had long since forsaken the teachings of the primarch.

But as he and Learchus marched towards the wall, he was filled with love for the soldiers who stood defiant before the tide of alien invaders. Here was the spirit of Ultramar best exemplified. In the common man, who stood tall against the horrors of the galaxy and was willing to die to protect what he believed in.

The two Space Marines stopped by one of the blazing fires on the edge of the wall, nodding in greeting to the soldiers clustered around its fleeting warmth. Uriel cast his gaze out over the ruined ground between the first two walls at the masses of aliens gathered before him. The collective exhalations of millions of creatures breathing in concert filled the valley, sounding like a single slumbering monster.

It would likely not be that simple, but if Lord Admiral Tiberius's plan succeeded then there was a chance that it might be. He had conferred with Sebastien Montante following his dissolution of the council, finding him awkwardly climbing into a suit of thermal overwhites and pulling on a webbing belt of ammunition.

'What are you doing, Fabricator Montante?' Uriel had asked.

'Well, now that the council has been dissolved, I think it's about time I picked up a gun and started fighting, don't you?'

Uriel folded his arms and said, 'When was the last time you fired a weapon, fabricator?'

'Ah, now let me think… probably during basic training, when I did my regulation service in the Defence Legion.'

'And how many years ago was that?' pressed Uriel.

Montante had the decency to look abashed as he said, 'About thirty years ago, but I need to fight, don't you understand?'

'I do, Sebastien, have no fear of that. You are one of the finest logisticians I have met, and your place is here. You have kept the soldiers supplied with food and ammunition, invested time, effort and money to ensure that all our military needs are met. But you are not a soldier, Sebastien, and you will die in the first minutes of an assault.'

'But—'

'No,' said Uriel firmly, but not unkindly, 'You can best serve your city in other ways.'

'Like how?'

'Well, you can start by telling me all about the orbital defences of Erebus: where they are, their status and how we get them firing again.'

Montante looked confused, 'But there's nothing left of them, Uriel. The torpedo silos expended their stocks of ordnance and the defence lasers fired until their power capacitors were dry.'

'Indulge me,' said Uriel.

And he had. Uriel and Montante spent the next two hours poring over maps, computing ranges, fuel to weight ratios, introducing all manner of variables into their discussions until they settled on the optimum course of action. Satisfied that the admiral's plan was indeed workable, Uriel had left, forcing Montante to swear an oath that he would not attempt to join the fighting men on the walls until the end came.

Then he had explained his idea to the other commanders. Initially sceptical, a cautious excitement gripped the senior officers as he outlined the results of his and Montante's labours, and they began to appreciate the scope of the plan.

Preparations were already underway and all they could do was hold until the battered remnants of the fleet were in position to strike. The operation was planned for the day after tomorrow and Uriel was anxious to begin. For too long they had retreated before the aliens. Now they had a chance to strike back.

Kryptman's pet Mechanicus had promised them a weapon to use against the tyranids, but had yet to deliver. Time was running out for Locard, and Uriel knew that the admiral's plan was the best shot they had at ending this war. It was a long shot, but as he looked down at the immensity of the tyranid swarm, he knew it was the only one they had.

He turned from the wall to see Learchus standing beside the brazier, his palms outstretched towards the flames. Uriel's brow furrowed in puzzlement, knowing Learchus was perfectly insulated from both the heat and cold within his power armour, before realising his sergeant was unconsciously copying the men around him. He smiled and listened to what Learchus was saying as he saw Chaplain Astador and Major Satria approach from further along the length of the wall. More men began drifting over from other fires as Learchus raised his voice to carry further.