An orderly turned the head onto its side and began to remove the jaw. He struggled to break the strengthened bone around the joint.

With a snap the jaw gave way, and like a fountain, a thin jet of glittering liquid arced onto the front of the orderly's smock.

The orderly began to scream as the liquid burned through the smock and into his chest. The other orderly pushed him to the floor and began to tear off the burning clothes as an eye-watering acid smell filled the air and grey smoke coiled upwards. The adept grabbed an emergency medikit from one of the infirmary's wall cabinets and began to work on the orderly washing down the hissing wounds with an alkali solution before it ate into his lungs.

'Inquisitor, you must leave.’ said the adept sharply as she pulled a field dressing from the kit. 'We have possible contamination.’

'There is no contamination.’ said the Pilgrim, its grating voice cutting through the orderly's gasping for air. 'The acid is a weak solution designed only to blind; your man will survive. It is produced by the Betcher's gland.’

'That's impossible.’ said Thaddeus, watching the trail of greenish liquid spluttering on the granite surface. 'The Soul Drinkers are a successor Chapter of the Imperial Fists Legion. The Fists' gene-seed never allowed Betcher's gland to develop, it was only a vestigial organ.’

'Exactly.’ said the Pilgrim, reaching towards the dissected head with a bandaged hand. It plucked the scrap of knotted flesh, the gene-seed, from the throat. 'Corrupt.’ he said, holding up the gene-seed. It was mottled and discoloured. 'The Soul Drinkers carry the stain of mutation upon them. The gravest mutation of all, for their very gene-seed is degenerating and the organs implanted in them are themselves being changed.’

'Mutation.’ repeated Thaddeus.

The survivors from House lenassis had reported a monstrous creature leading the Soul Drinkers, with legs like a giant spider and vast psychic powers. He had been sceptical about such talk, but now he could not dismiss the image so easily. The Soul Drinkers were mutants, and with their gene-seed affected they would slide downhill fast.

That made them desperate. And desperation bred atrocity. Whatever their plans, the Soul Drinkers were heading faster and faster towards a state where they were mutated beyond all semblance of humanity.

Thaddeus had always known that his patience would have its limits. But now time had suddenly begun to press on him more strongly. Everyone was running out of time.

And Thaddeus had next to nothing to go on. But he would have to make it do.

He left the infirmary at a jog, heading towards his chambers through the cold, draughty stone corridors of the fortress. He heard the Pilgrim following him but had lost the strange creature by the time he reached his room. He flung open the chest again and pulled out another piece of evidence. It was something he had thought useless when Sister Aescarion had presented it to him - a thin brass plaque with the names of hundreds of adepts tooled into it, the adepts who had worked at the Hive Quintus outpost for the last few decades. There were hundreds of names in tiny, precise type, from the overseers of the menials and servitor engineers to the series of adepts senioris who had commanded the outpost.

The Pilgrim arrived at the door. 'Inquisitor? You have found something?'

Thaddeus looked round. He wished very much that he could have conducted this investigation without the Pilgrim, but he had to tolerate the creature for the insights it had into the renegade Chapter.

'Perhaps,' he replied. 'The Soul Drinkers were at the outpost for a reason. They left at least one of their own behind. Why? Why go to a planet consumed by plague, and journey into the heart of its worst city to fight a battle? Why break into a Mechanicus outpost that produced nothing of any real interest or importance? The rock samples were worth nothing. They had no specialised equipment or weapons. What did they have, Pilgrim?'

The Pilgrim tilted its head slightly, and Thaddeus had an unpleasant feeling that it might be smiling somewhere under there. 'They had people, inquisitor. A hundred Mechanicus adepts. Adepts who had not always worked at that one outpost.'

Thaddeus sat back onto his bed, still holding the plaque. 'One of them knew something. And it was enough for the Soul Drinkers to go down there and capture them. If they took a prisoner and got them off the planet they could have everything they need to know.'

Thaddeus stopped. The Imperium was so immensely vast, and the Adeptus Mechanicus such an insanely complicated organisation - from the Fabricator General on Mars to the lowliest menials and servitors labouring on forge worlds and in workshops across the known galaxy. How could he ever hope to track a single adept, even with the resources of an inquisitor? One tiny, meaningless worker who was no Chaos cultist or rogue secessionist, but a nobody in a galaxy of nobodies?

'No.’ he said out loud to himself. 'I'm not letting this lead slip.' He flicked on the vox-bead on his collar. 'Colonel Vinn? Assemble your best infiltrators and scouts, ready for review at the spaceport in half an hour. See what you can do about commandeering us a shuttle for loading into the Crescent, it doesn't need much range but it will need stealth and assault capabilities. The best crew, too. Pull strings if you have to. Out.'

Thaddeus had not been in the warzone sector for long, but had done basic research into the sector's power structures. He knew that the information he needed might just be available if he was fast, skilled and lucky. It had been some time since he had last used a weapon in execution of his duty as an inquisitor, and he was mildly surprised to find that he was looking forward to doing so again.

IT WAS QUIET to the galactic west, a wasteland tract of space where few but hardy prospectors and driven missionaries bothered to go. The thick band of stars that marked out the galactic disk was empty for light years ahead, and pilot second class Maesus KinShao knew that without staging posts or spaceports there was little chance of an assault coming from that direction. But it was his duty to be here -he was a servant of the Emperor cocooned in the cockpit of his Scapula-class deep space fighter, a member of a squadron with orders to defend the western frontier of the warzone.

The Scapula had a six-man crew - KinShao, a navigator, three weapons officers and an engineer. There were seventy such craft spread out across this section of the frontier, each armed with sophisticated intruder detection sensors and a bellyful of ordnance.

KinShao called up the HUD screen to show an overview of his squadron's positions. Twenty fighters, each the size of a small cargo ship, hung in space with their sensor fields overlapping so nothing could get through. If any craft tried to escape from the warzone, or to break into it, the craft would be spotted and challenged. If it was remotely suspicious, it would be destroyed with a hail of guided munitions. The Scapulas were some of the most complex and valuable assault craft the sector naval command could muster, and KinShao loved the feeling of the massive metal structure all around with him. For now, though, everything was quiet, and the blazing war a few light hours to the galactic east seemed much further away.

'Squadron, sound in.’ came the crackly voice of the squadron commander over the comms. The commander was young and aristocratic, but he seemed solid enough. KinShao hadn't flown under him in anger yet.

'KinShao, red seven. What's the problem?'

'Blue five is reading anomalies. Anything else on anyone's scopes?'

KinShao relayed the communication to his navigator, Shass.