Gasps of shock and cries of dismay were uttered by many of the fleet officers. Nemiel scarcely heard them. He felt only the rushing of blood in his temples and the awful coldness that seemed to spread like a wound through his chest. The primarch's words echoed in his mind, but they didn't make any sense. They couldn't make sense. His mind refused to accept them.

He turned to Kohl. The veteran sergeant's expression was stoic, but his eyes were glassy with shock. The rest of the Astartes also bore the news in silence, but Nemiel could see the words sinking into them like a torturer's knife. The Redemptor shook his head slowly, as though he could banish the awful knowledge from his head.

The primarch waited patiently for the assembly to regain a sense of order before continuing. He keyed a series of controls on the side of the hololith projector, and the device flickered into life. A detailed, three-dimensional map of the Eriden sector flickered into existence before the assembly. Imperial systems were displayed in bright blue, while at their heart, the Isstvan system pulsed an angry red. Jonson pressed another set of keys, and many of the star systems surrounding Isstvan changed colour in an irregularly-expanding sphere. Nemiel and many others in the assembly were shocked to see a score of systems switch from blue to red, and scores more flicker from blue to a dull grey.

'The reasons for the Warmaster's rebellion are unclear, but the magnitude of his actions cannot be overstated. News of the rebellion has spread like a cancer through the sector and beyond,' Jonson said, 're-igniting old tensions and territorial ambitions. Some governors have openly declared for Horus, while others see the rebellion as an opportunity to build petty empires of their own. In the short space of just two and a half months, Imperial authority in the Ultima Segmentum has been severely compromised, and dissent is beginning to spread into Segmentum Solar as well.'

Jonson paused, studying the pattern of unrest represented on the map as though it held secrets that only he could see. 'It's likely that agents loyal to the Warmaster are operating all across both Segmenta, helping fuel the growing dissent. Note how the outbreaks of lawlessness spread from system to system along the most stable warp routes leading back to Terra, the direction from which any large-scale retaliation is certain to originate.'

Nemiel took a breath, drawing on the psycho-linguistic rotes he'd learned in training to suppress his emotions and focus on the data suspended in the air above the projector. To his eyes, the instances of revolt in the Ultima Segmentum appeared haphazard, but Lion El'Jonson was famous within the Legion - if not elsewhere - for his strategic genius. He had an almost intuitive ability to understand the balance of forces in a conflict and predict its course with stunning accuracy. It made him one of the Emperor's finest generals, second only to Horus himself - and in the opinion of many Dark Angels, perhaps even greater than that.

'As soon as word of the Warmaster's rebellion reached Terra, the Emperor began assembling a punitive force to confront the rebel Legions and take Horus into custody,' Jonson continued gravely. 'According to the despatch we received, a full seven Legions, led by Ferrus Manus and the Iron Hands, are en route to Isstvan, but it will be at least another four to six months before they arrive. In the meantime, Horus has redeployed his forces to Isstvan V, and is in the process of fortifying the planet in anticipation of the coming attack.'

Out of the corner of his eye, Nemiel saw Kohl fold his arms across his chest. He glanced at the Terran sergeant, and saw a bemused frown cross his weathered face.

'The next few months are going to be crucial for Horus and the rebel Legions,' Jonson said. 'The Warmaster knows that the Emperor will respond with all the force he has available. I now believe that our deployment to the Shield Worlds was part of an effort to scatter the Imperium's most loyal servants as far as possible in order to minimize the number of Legions he would have to face at any given time. Even so, a strike force of seven full Legions poses a dire threat to Horus's survival; surviving a planetary siege from such a force, let alone defeating it, will require transforming Isstvan V into a veritable fortress world. That will require an enormous amount of supplies and equipment on very short notice - the sort of materiel that only a fully-operational forge world can provide.'

The primarch adjusted the controls on the projector, and the sector view blurred, focussing in closely on the Eriden subsector and its neighbours. One system very close to Isstvan, stubbornly blue in a sea of grey and red, was suddenly highlighted.

'This is the Tanagra system, located at the edge of the adjoining Ulthoris sub-sector. As you can see, it is only fifty-two-point-seven light years from Isstvan, and lies along the most stable warp route to and from Terra. It also happens to be one of the most heavily industrialised systems in the entire sector, with a Class I-Ultra forge world named Diamat and more than two dozen mining outposts and refineries scattered throughout the system. Historically, Tanagra was rediscovered by Horus's Legion and became compliant relatively early in the Great Crusade. It has been a key logistical centre for the region ever since.' Jonson indicated the highlighted system with a thoughtful nod. 'It is no exaggeration to say that whoever controls the Tanagra system might well determine the fate of the entire Imperium.'

Murmurs spread through the assembly. The primarch's voice carried easily over them all.

'The Warmaster's treachery caught all of us off-guard - just as he intended it to do,' Jonson said. His voice took on a cold, angry edge. 'At this stage, our forces are too deeply enmeshed here in the Shield Worlds to respond quickly to Horus's treachery; the best estimates of my staff indicate that it would take us nearly eight months to conclude our offensive operations, even on an emergency basis, and re-position ourselves for a strike against Isstvan. Even if we could move more quickly, Horus's agents would be able to alert the Warmaster in time to organise a counter-move.'

Jonson paused, once more surveying the shocked faces surrounding him, and his lips quirked in a predatory smile. 'A small, hand-picked force, however, might accomplish what an entire Legion cannot.' He pointed to the Tanagra system. 'Diamat is the key. If we can keep its industrial wealth from Horus's hands, he and his Legions will be as good as beaten.'

The murmurs among the assembly grew to an excited buzz. Suddenly, Nemiel understood the frenetic activity occupying much of the fleet, and the primarch's summons from the planet below. He'd been chosen, along with all the other Astartes who'd come aboard. A fierce pride swelled in his breast. Looking about, he could see that many of his brethren were feeling it as well.

Jonson raised a gauntleted hand for silence. 'As many of you already know, I've issued orders for many of our reserve squadrons to resupply and prepare for immediate deployment. I have also summoned two hundred veterans - the most I feel we can spare - from our chapters on the planet below. As you're well aware, the Shield Worlds campaign is at a critical juncture. We've been fighting the Gordians and their degenerate xenos allies for months, and this is our best opportunity to break the alliance once and for all. My senior staff will be transferring aboard the grand cruiser Decimator within the hour, and will remain behind to conclude operations here in the Shield Worlds as quickly as possible. I will personally lead the expedition to Diamat, with a battle group of fifteen warships. We will travel light, leaving the slower tenders and supply vessels behind, and trust that we will be able to replace our stores when we reach Tanagra. Our Navigator believes that if current warp conditions persist, we should reach Diamat within two months.'