'Then what is it?'

'This is a guess, but it looks like this particular poison induces a form of anaemic hypoxia. Once it enters the bloodstream, it's absorbed exponentially by the red blood cells, in preference to oxygen. With the Warmaster's accelerated metabolism, the toxin was carried efficiently around his system, damaging his tissue cells as it went, so they were unable to make proper use of the reduced oxygen content.'

'So where did it come from?' asked Loken.

'I thought you said the Warmaster was immune to such things.'

'And so he is, but this is like nothing I've ever seen before… it's as though it's been specifically designed to kill him. It's got precisely the right genetic camouflage to fool his enhanced biological defences and allow it to do the maximum amount of damage. It's a primarch killer - pure and simple.'

'So how do we stop it?'

'This isn't an enemy you can take a bolter or sword to, Captain Loken. It's a poison,' he said. 'If I knew the source of the poisoning, we might be able to do something.'

'Then if we found the weapon that did this, would that be of some help?' asked Loken.

Seeing the desperate need for hope in the captain's eyes, Vaddon nodded. 'Maybe. From the wound shape, it looks like a stab wound from a sword. If you can retrieve the blade, then maybe we can do something for him.'

'I'll find it,' swore Loken. He turned from Vaddon and made his way to the theatre door.

'You're going back there?' asked Torgaddon, running to catch up with him.

'Yes, and don't try to stop me,' warned Loken.

'Stop you?' said Torgaddon. 'Don't be such a drama queen, Garvi. I'm coming with you.'

Recovering a Titan after action in the field was a long and arduous process, full of technical, logistical and manual difficulties. Entire fleets of vessels came down from orbit, bringing huge lifters, enormous diggers and loading machines. The delivery vessels had to be dug from their impact craters, and an army of Mechanicum servitors were required to facilitate the process.

Titus Cassar was exhausted. He'd spent the better part of the day prepping the Titan for its recovery and everything was in readiness for their return to the fleet. Until they were recovered, there wasn't much to do except wait, and that had become the hardest part of all for the men left behind on Davin's moon.

With time to wait, there was time to think, and with time to think, the human mind could conjure all manner of things from the depths of its imagination. Titus still couldn't believe that Horus had fallen. A being of such power, like unto a Titan himself, was not meant to fall in battle - he was invincible, the son of a god.

In the shadow of the Dies Irae, Titus fished out his Lectitio Divinitatus chapbook and, once he was satisfied he was alone, began to read the words there. The badly printed scripture gave him comfort, turning his mind to the glory of the divine Emperor of Mankind.

'Oh Emperor, who is lord and god above us all, hear me in this hour of need. Your servant lies with death's cold touch upon him and I ask you to turn your beneficent gaze his way.'

He fished out a pendant from beneath his uniform jacket as he read. It was a delicately wrought thing of silver and gold that he'd had one of the blank-faced servitors fashion for him. A silver capital ''I'' with a golden starburst at its centre, it represented hope and the promise of a better future.

He held it clasped to his breast as he recited more of the words of the Lectitio Divinitatus, feeling a familiar warmth suffuse him as he repeated the words.

Titus sensed the presence of other people behind him a second too late and turned to see Jonah Aruken and a group of the Titan's crew.

Like him, they were dirty and tired after the fight against the monsters of this place, but unlike him they did not have faith.

Guiltily, he closed his chapbook and waited for Jonah's inevitable barb. No one said anything, and as he looked closer, he saw a brittle edge of sorrow and the need for comfort in the faces of the men before him.

'Titus,' said Jonah Aruken. 'We… uh… that is… the Warmaster. We wondered if…'

Titus smiled in welcome as understood what they'd come for.

He opened his chapbook again and said; 'Let us pray, brothers.'

The medical deck was a sterile, gleaming wilderness of tiled walls and brushed steel cabinets, a warren of soulless glass rooms and laboratories. Petronella had completely lost all sense of direction, bewildered by the hasty summons that had brought her from the moon's surface back to the Vengeful Spirit.

Passing through the bloody embarkation deck, she saw that the upper levels of the ship were in pandemonium as word of the Warmaster's death had spread from vessel to vessel with all the fearsome rapidity of an epidemic.

Maloghurst the Twisted had issued a fleet-wide communique denying that the Warmaster was dead, but hysteria and paranoia had a firm head start on his words. Riots had taken hold aboard several ships as doomsayers and demagogues had arisen proclaiming that these were now the end times. Army units had been ruthlessly quashing such malcontents, but more sprang up faster then they could stop them.

It had been scant hours since the Warmaster's fall, but the 63rd Expedition was already beginning to tear itself apart without him.

Maggard followed Petronella, his wounds bound and sealed with syn-skin by a Legion apothecary on the journey back to the Warmaster's flagship. His skin still had an unhealthy pallor and his armour was dented and torn, but he was alive and magnificent. Maggard was only an indentured servant, but he had impressed her and she resolved to treat him with the respect his talents deserved.

A helmeted Astartes warrior led her through the confusing maze of the medicae deck, eventually indicating that she should enter a nondescript white door marked with a winged staff wrapped in a pair of twisting serpents.

Maggard opened the door for her and she entered a gleaming operating theatre, its circular walls covered, to waist height, in green enamelled tiles. Silver cabinets and hissing, pumping machines surrounded the Warmaster, who lay on the operating slab with a tangled web of tubes and wires attached to his flesh. A stool of gleaming metal sat next to the slab.

Medicae servitors lurked around the circumference of the room, set into niches around the wall, and a gurgling machine suspended above the Warmaster fed fluid and blood into his body.

Her eyes misted to see the Warmaster brought so low, and tears came at this violation of the natural order of things. A giant Astartes warrior in hooded surgical robes approached her and said, 'My name is Apothecary Vaddon, Miss Vivar.'

She brushed her hands across her eyes, conscious of how she must look - her dress torn and caked with mud, her eyes blackened with smudged make-up. She started to hold her hand out for a kiss, but realised how foolish that would be and simply nodded.

'I am Petronella Vivar,' she managed. 'I am the Warmaster's documentarist'

'I know,' said Vaddon.

'He asked for you by name.' Sudden hope flared in her breast. 'He's awake?'

Vaddon nodded. 'He is. If it was up to me, you would not be here now, but I do not disobey the word of the commander, and he desires to speak with you'

'How is he?' she asked.

The apothecary shook his head. 'He fades in and out of lucidity, so do not expect too much of him. If I decide it is time for you to leave, then you leave. Do you understand me?'

'I do,' she said, 'but please, may I speak with him now?'

Vaddon seemed reluctant to let her near the Warmaster, but moved aside and let her pass. She nodded her thanks and took a faltering step towards the operating slab, eager to see the Warmaster, but afraid of what she might find.