'Then you understand why I cannot allow that to happen,' Luther said. 'Not here. Not on my watch. The people of Caliban are innocent and undeserving of such a fate, and I won't allow such a thing to happen.'

Israfael rose slowly to his feet and faced Luther. 'What you're contemplating is against Imperial law,' he said gravely. 'Indeed, it smacks of treason.'

'That's easy for you to say,' Luther snarled. 'This isn't your home. These aren't people you've sworn a solemn oath to defend.'

'Of course I have!' Israfael shot back, his voice rising. 'Am I not an Astartes? The Imperium—'

'The Imperium brought us to this!' Luther roared. He rounded on Israfael, his face anguished and his hands clenched into fists. 'There were no rebellions before you arrived, no obscene rituals or human sacrifices! There was order, and law, and virtuous men who stood between the innocent and the terrors of the forest. It was your people who did this, who dug too deeply and grasped for too much, and now me and mine will pay the price!'

Israfael tensed, and the air around him literally crackled with furious power. Astelan turned slightly to face the senior Librarian, his hands drifting slowly to his weapons. Zahariel recalled the chapter master's oath at Sigma Five-One-Seven and understood how perilous the situation had become. He rushed forward, placing himself between Luther and Israfael.

'We are all brothers here,' he said firmly. 'Neither Calibanite nor Terran, but Dark Angels, first and always. If we forget that, even for a moment, we are lost. Then who will protect our people, Master Luther?'

Luther's gaze fell on Zahariel. For a long moment he was silent, until his expression grew bleak and his fists slowly unclenched. The Master of Caliban turned away, resting his hands upon the heavy desk.

'Zahariel is right, of course,' he said at last. 'I hope you will forgive my intemperate tone, Brother Israfael.'

'Of course,' Israfael said stiffly.

Luther worked his way around the desk and settled slowly onto the throne-like chair. His expression was distant, his eyes haunted.

'I must meditate on this,' he said in a hollow voice. 'Too many lives are at stake to act precipitously. For now, we must make sure this rot has spread no further. Zahariel, send the scouts into the Northwilds. Have them reconnoitre every industrial site in the sector and search for signs of further corruption. Check the Administratum's records and find out which engineers were assigned to Sigma Five-One-Seven, then pass their identities on to the Jaeger regiments at the Northwilds arcology. They are to be captured and delivered to Aldurukh immediately.' He sighed. 'Brothers, I realize this is well outside the scope of our temperament and training, but this matter must be handled with the utmost secrecy. There is no one else we can trust with this.'

Zahariel bowed his head respectfully. 'I'll see to it at once.'

Luther turned to Astelan. 'Chapter master, as of this moment I'm putting you in command of Caliban's defence forces. Place our brothers on a war footing. I want strike teams ready to deploy in case any more ritual activity is detected, but no one is to act without my express authorization. Understood?'

'Understood,' Astelan replied gravely. 'We will stand ready, my lord.'

'Let's at least send some scout teams into the arcology as well,' Zahariel said. 'The sorcerers are most likely practicing their rituals close to the thermal core. If we could locate them quickly, we could—'

Luther held up a restraining hand. 'Not yet. If we start suddenly committing our warriors now, during a relative lull in civil unrest, it will almost certainly lead to renewed scrutiny from the Administratum. That's something we can ill afford at this point.'

'Magos Bosk will have to be informed of the destruction of Sigma Five-One-Seven,' Israfael pointed out.

'If there are any reports to be made, I will make them,' Luther said sternly. 'None of you are to speak of what happened at the site, as a matter of operational security. Understood?'

The four Astartes nodded.

'Then you are dismissed,' Luther said. 'Except for you, Lord Cypher. I have some questions to ask you.'

Israfael turned on his heel and left the room without a word. Astelan was close behind, his expression eager. Zahariel hesitated for a moment, torn by feelings of doubt. Only he saw Lord Cypher glide quietly from the shadows to stand beside the Grand Master's throne-like chair.

He wasn't certain what disturbed him more: the sight of Luther staring down at his own hands, his expression anguished - or the enigmatic smile that passed like a shadow across Lord Cypher's face.

Lightning flashed angrily overhead, banishing the darkness for the space of a heartbeat and dazzling Zahariel's sensitive eyes. Thunder crashed, vibrating along his bones, and raindrops spattered heavily against his cheeks. He paused, struggling to calm his thoughts and banish the spots of colour from his vision. When his vision cleared, he set his feet upon the spiral path once more.

It had been more than a week since the encounter at Sigma Five-One-Seven. Orders had gone out immediately from the Rock; the Scout chapter on Caliban had gone into action within hours, commencing a building-by-building search of every industrial site within the Northwilds sector. At the same time, a records search provided the identities of the Terran engineering team that had been assigned to Sigma Five-One-Seven. The information had been passed on to the Jaeger regiments deployed to the Northwilds arcology, but it was learned that the arcology's so-called Terran Quarter had been looted and burned during the first cycle of riots, and the inhabitants had been relocated for their own safety. The problem was that details of the relocation had been lost amid the chaos, and now no one knew for sure where many of the Terrans had wound up. The Jaegers were trying to locate them, but the local regiments had few troops to spare because of the continued threat of rebel attack. Though Luther seemed willing to let the arcology burn in order to track down the sorcerers, there was no practical way to issue such an order without raising a chorus of questions all along the chain of command. Zahariel had heard, indirectly, of the confrontation between Luther and Magos Bosk over the destruction of Sigma Five-One-Seven, and by all accounts it had been epic. Bosk had been livid over the loss of so much industrial capacity, and it had taken every bit of Luther's charisma and authority to prevent her once more from breaching protocol and reporting the situation to the Adeptus Terra.

They were running out of time. Every passing hour was a boon to the fugitive sorcerers, who were no doubt working to further their plan somewhere in the labyrinthine depths of the arcology. Though the Jaegers were making a concerted effort to locate them, the fact was that there were large parts of the arcology that they couldn't penetrate due to the possibility of rebel attack. These no-go zones provided countless safe havens for the sorcerers to continue their work without fear of interruption.

The only answer was to send in the Legion, Zahariel knew. A level-by-level sweep, conducted by their Scout chapter and supported by one or more assault chapters could brush aside any rebel resistance and isolate the real threat within hours. Such an operation, if conducted with proper ruthlessness, might even convince the rebel leaders that further resistance was pointless, and put an end to both threats at the same time.

The problem was that only Luther had the authority to put such a plan into action, and he had gone into seclusion within hours of receiving the report on Sigma Five-One-Seven. No one could even say for certain where the Master of Caliban had gone, save for the enigmatic Lord Cypher, and he was sworn to silence. Zahariel had prevailed upon Cypher to carry close to a dozen messages to Luther urgently requesting permission to send the Legion into the arcology, but not a single one had been answered.