Remiel's eyes narrowed. 'Are you so certain he will agree to this?'

'Of course,' Zahariel replied, putting more sincerity into his voice than he actually felt. 'Do you imagine Caliban's greatest living knight would hold his honour so cheaply?'

If Remiel sensed the doubt in Zahariel's heart he did not let it show. 'Very well,' he said with a curt nod. 'Sar Daviel will join us to help coordinate our forces.' He turned to Lady Alera. 'Alert our remaining cells and organise a search of the sub-levels at once. If you locate the Terrans, do not attempt to engage them. Do you understand?'

Alera nodded. On impulse, she reached out and laid her hands on Remiel's own. 'Are you sure of this?' she asked. 'You swore you'd never return to the fortress. You said they'd betrayed everything you believed in. How can you trust them now?'

Remiel sighed. 'This isn't about trust,' he said to her. 'It's about honour, and a last chance at redemption. I owe it to them, Alera. I owe it to myself.' He gently pushed her hands away.

'Now go. Zahariel is right. We haven't much time.' He smiled. 'I will return with the knights of Caliban at my back, or I will not return at all.'

Las-bolts hissed past Nemiel as he plunged down onto Magos Archoi and the rebel soldiers. His bolt pistol thundered, and two of the officers collapsed with gaping wounds blown in their chests. Archoi fell back from the Redemptor's attack, screeching in binaric, and his acolytes rushed forward, drawing high-powered laspistols from their belts.

Nemiel struck down another of the rebels with a crackling swipe of his crozius. A las-bolt struck the side of his helmet like a hammerblow, causing his visual displays to waver, and a warning icon told him that the helm's integrity had been compromised. He shot the officer point-blank, blowing him off his feet - and then felt a hail of blows as the acolytes unleashed a volley of pistol shots into his chest.

The acolytes were blurs of motion, their muscles undoubtedly stoked by combat drugs and adrenal boosters. Nemiel felt a half-dozen bolts pummel his breastplate, then a flash of searing pain over his primary heart. For a moment his vision threatened to grey out as his body fought to stave off the effects of shock, then abruptly the pain vanished and his mind cleared with a cold rush as his suit dumped pain blockers and stimulants into his bloodstream.

A boltgun let off a rapid burst over Nemiel's shoulder and one of the acolytes fell in a spray of blood and fluids. The Redemptor shot the remaining acolyte twice, and finished him off with a backhanded blow of his crozius. He was leaping forward before the traitor's body had hit the floor, racing down the narrow aisle after the fleeing form of Magos Archoi.

Brother-Sergeant Kohl ran alongside Nemiel from high atop the siege gun's hull, firing shots from his bolt pistol at every tech-adept who got in his path. Behind Nemiel, Marthes crouched atop the vehicle and fired another blast up at the skitarii who were firing down from the gantry-way they had just vacated. The catwalk blew apart in a storm of molten fragments, plunging the survivors to the permacrete floor two storeys below. Techmarine Askelon landed heavily on the permacrete floor, pushing onward despite his suit's heavily damaged systems. Vardus and Ephrial brought up the rear, cutting down any soldier or tech-adept who tried to circle behind the squad.

Nemiel bore down on the magos like a Calibanite Lion, his lips pulling back in a feral snarl. If it was the last thing he did, he was going to make sure the traitor felt the Emperor's justice. Behind and above him, he heard Kohl shout a warning just as the Praetorians charged at him from the gap between two of the parked siege guns.

The shout saved his life. Nemiel turned towards the sound and ducked low, barely avoiding a swinging power claw that would have torn his head off. A second Praetorian lunged at him, scoring a deep gouge across his hip with a glowing power knife. Nemiel brought his crozius down on the skitarii's knife hand, smashing the weapon from the warrior's grip, and pumped three rounds into the Praetorian's chest. The warrior staggered as the rounds punched through his armour, but his chemically-charged nervous system kept him upright.

There were four of the hulking, gene-modded warriors: the one with the power claw reached for Nemiel's gun arm, while the second Praetorian brought his weapon systems to bear as he tried to circle around the Redemptor's flank. The remaining pair of skitarii were stymied by Brother-Sergeant Kohl, who leapt down onto the Praetorians with a furious shout. His power sword slashed down in a glowing arc, slicing through one warrior's weapon arm with a shower of sparks and spurting fluids.

The Praetorian circling to Nemiel's right went down in a blaze of bolt pistol fire from Techmarine Askelon; seeing his opportunity, the Redemptor pivoted on his left heel and smashed his crozius into the other skitarii's head. The warrior died just as his claw snapped shut on Nemiel's forearm, leaving three deep, bubbling gouges on the black vambrace before collapsing to the ground.

Kohl despatched the wounded Praetorian in front of him with a brutal cut that sliced open his armoured torso. The last of the skitarii raised his weapon-arm and took aim at the sergeant, only to die as Nemiel put three bolt pistol rounds into his back at point-blank range.

Nemiel whirled, looking for the traitor magos, but Archoi was nowhere to be found. The Praetorians had accomplished their goal, buying time for the traitor to escape with their lives. The surviving tech-adepts had fled as well, scattering like vermin down the narrow lanes on the floor of the assembly building. The Redemptor started to pursue them, but Brother-Sergeant Kohl called for him to stop.

'We don't have time to chase rabbits,' Kohl said as las-bolts spat down at them from the gangway. 'We've got to get a warning back to our brothers and to the Dragoons.'

Vardus, Ephrial and Askelon unleashed a blistering volley up at the skitarii, killing several and forcing the rest to withdraw. Nemiel wavered, drawn by the siren song of vengeance, but reason and training ultimately won out over emotion. 'You're right, brother,' he said to the sergeant. 'We've just forced Archoi's hand; he'll have to order his forces into action at once. Askelon!' he called, turning to the Techmarine. 'What's the quickest way out of here? We haven't got a moment to lose!'

In fact, they were already ten minutes too late.

Archoi's plan had been a hasty one, devised on the spur of the moment as he stood over the bullet-riddled body of his former master Vertullus and received word that, at the absolute last moment, an unknown force of Astartes had arrived in orbit to save the beleaguered forge world. His takeover was already well underway, with loyal units of tech-adepts and skitarii murdering Vertullus's loyal supporters and herding the rest into the old shelters situated deep beneath the manufactories at the base of the great volcano. When the admiral in charge of the Warmaster's fleet informed him that they would have to withdraw, Archoi promised him that when they returned to Diamat, he and his people would be ready. It was that, or face certain execution once that bastard Kulik caught wind of his crimes. As the last of the rebel ships were pulling out of vox range, the magos fired off a compressed burst of binaric that outlined his scheme. The crucial element that the whole plan hinged on was a certain date and an approximate time, two and a half weeks away. Now that time had arrived, and Archoi had to trust that the Warmaster would not be late.