At each of the structures highlighted on Nemiel's images, the squad would take up a defensive position and let Brother Askelon go ahead to inspect the building's contents. Each time the Techmarine would emerge, shaking his head, and the squad would move on to the next building down the line.

By midnight they were half-way through their search pattern and were doubling back eastward, heading for the warehouse districts on the other side of the access road. They were well north of the billets set aside for the Astartes ground force, and could see the towering, fortress-like manufactories off to the north, spreading out in a rough circle from the foot of the slumbering volcano. Tall, narrow smokestacks and squat cooling towers rose into the sky like the bones of dead gods, blackened and pitted by age. Cold, white lights shone like stars from the slopes of the conical mountain, while off to the north-east, the towering monolithic structures of the Titan foundry shone with sparkling pinpoints of sapphire, crimson and emerald.

'I've moved through dead cities that weren't as eerie as this,' Brother-Sergeant Kohl murmured beside Nemiel. 'I thought forges were like mechanical beehives. Where is everyone?'

Nemiel shrugged, his eyes searching the darkness off to the south for signs of danger just as Kohl kept his attention focused on the north. 'Magos Archoi mentioned at one of the strategy meetings that he'd ordered all surviving tech-adepts and acolytes into a series of deep shelters near the heart of the complex. Only a few hundred volunteers are still above ground or in orbit, working with the battle group and helping supply our forces on the ground. Archoi said they'd suffered enough losses during the last raid, and he wasn't going to permit any more if he could help it.'

Kohl grunted dubiously. 'It's an awfully clean battlefield, don't you think?'

Nemiel glanced sidelong at the sergeant. 'What are you talking about?'

Brother-Sergeant Kohl shrugged, eyeing the walls of the dark buildings to his right. 'Where are the shell holes? The scorch marks? Where are the burnt-out buildings? If the fighting was so heavy in this sector, why haven't we seen any sign of it yet?'

The observation nearly stopped Nemiel in his tracks. Something tugged at the back of his mind; something else strange and out of place, but he couldn't quite put a finger on it.

'Maybe the battle sites are still up ahead,' he replied, frowning to himself. 'Archoi and his warriors came at us from the northeast. Let's see what lies up ahead.'

But for the next three hours Nemiel and Kohl saw only more of the same: building after building, arrayed in laser-perfect lines, their permacrete walls unblemished save for decades of stains and pitting etched by acid rain. Nemiel's disquiet grew stronger. Something was very wrong.

Barely two hours before dawn, Askelon found something. They had reached an enormous depot building, two storeys high and wide enough for a pair of super-heavy tanks to pass through its entry-way side-by-side. The Techmarine moved stealthily inside while the rest of the squad watched for Mechanicum patrols. He was back in less than five minutes. 'You need to see this,' he said to Nemiel.

The Redemptor rose to his feet and signalled for the squad to follow him. Askelon led the warriors along a convoluted route that brought them past the cordon of sensors surrounding the perimeter of the structure. Soon, Nemiel found himself standing in a vast, cavernous structure, supported by soaring metal arches curving high overhead.

'It's empty,' he said to Askelon. His voice echoed faintly in the deserted building.

'No. Not quite,' the Techmarine said, turning about and pointing to the inner surface of the depot's towering metal doors.

Nemiel turned about and saw that the metal slabs were splashed and streaked with dried gore.

He stepped forwards, his enhanced vision easily picking out details even in the near-absence of light. 'Lots of carbon scoring,' he observed. 'Looks like high-power lasgun fire.'

Kohl nodded, stepping up beside Nemiel. A gauntleted finger moved through the air, roughly tracing the outline of the stains. 'I'd guess ten to fifteen individuals, shot at close range,' he reckoned. 'Judging by the intensity of the lasgun fire, they must have been nearly blown apart. This wasn't a battle. It was an execution.'

'I thought much the same thing,' Askelon said. He stepped up to the doors and laid a fingertip against one of the dried stains. 'Not all of this is blood. Some of it is bionic lubricant or coolant.'

Brother-Sergeant Kohl scowled. 'Didn't Magos Archoi say that Arch-Magos Vertullus was killed during the fighting?'

Nemiel felt his skin grow cold. 'The magos never said who it was that killed Vertullus.'

Kohl stared at Nemiel. 'You think there's been some kind of coup?' The veteran sergeant sounded incredulous.

'Archoi was in the area with a large force of Praetorians,' Nemiel mused. 'The attack would have given him an excellent opportunity. He could kill Vertullus and the other senior magi, dispose of the bodies, and no one the wiser.' Suddenly Nemiel's eyes widened. 'Bodies. By the Emperor, that's what was missing. The bodies!'

Kohl shook his head in consternation. 'What are you talking about now?'

'Governor Kulik said there was an entire company of Dragoons covering the entrance to the southern gateway,' Nemiel explained. 'The rebels supposedly overran them. But there were no dead Imperial troops anywhere. What happened to the bodies?'

The sergeant frowned. 'I don't know. I doubt they just got up and walked away.'

'But perhaps they did,' Nemiel said. 'What if the Dragoon company guarding the gateway was betrayed by the very people they were there to defend?'

Kohl's face turned grim. 'That would mean Magos Archoi is in league with Horus,' he said. 'We need to inform the primarch at once!'

Nemiel held up a hand. 'Not yet. Not without more proof than this,' he said, indicating the blood-splashed wall. He paused, contemplating the tall doors, then glanced back at the empty, echoing space. 'What was Vertullus doing here in the first place?' he wondered. 'Maybe the war machines we're looking for were stored here, and he'd come to check on them?'

'The building's certainly big enough to hold six to eight large vehicles,' Askelon confirmed. 'There's dust and debris in the corners that suggest this place hadn't seen much activity in a very long time. The question is: where are the war machines now?'

Nemiel's mind raced as he tried to think through the mystery. 'If Archoi is with the rebels, he was in the process of trying to hand over the war machines to them when we arrived,' he said. 'If the vehicles had sat in a depot for a century and a half, they would have been in need of some refurbishment. He would have taken them somewhere he and his minions could work on them without being disturbed - possibly even as early as several weeks before Horus's raid.'

Askelon shook his head. 'The manufactories would have been working at full output at that point. They couldn't possibly have used them.'

'Well, where else would they have the facilities they would need?' Nemiel asked.

The Techmarine spread his hands. 'Other than the Titan foundry, I can't think of any,' he said. 'And I guarantee you, the Legio adepts would take a dim view of someone else using their facilities.'

Nemiel looked to Kohl. 'Except that Legio Gladius isn't here. Someone else is running the lights over at the foundry.'