Zahariel, however, wasn't the least bit cowed. He folded his arms and glared at the rebels. 'I'm going to give you just one chance to put those guns away,' he said in a quiet voice.

Thuriel chuckled. 'Or what?' he shot back. 'I've heard stories about the legendary toughness of the Astartes, but I rather doubt even you would survive a point-blank shot from a plasma gun.'

'None of us would survive, you idiot,' Zahariel said scornfully. 'In a small room like this the thermal effects would incinerate us all. Now, I'm going to say this one last time. Put your weapons away, or this parley is finished.'

'Parley?' Thuriel said incredulously. 'Have you not heard anything I've said? Unless you're here to accede to our terms, we have nothing to discuss.'

Before Zahariel could reply, the door behind the rebel soldiers banged open. Sar Daviel appeared, shoving his way roughly past the startled gunmen. Behind him came Lady Alera, her face pale and her expression fierce. She, in turn, was followed by a third figure, stoop-shouldered and lean and clad in a plain white surplice identical to Zahariel's own. The Librarian looked into the figure's seamed face and felt a shock like a thunderbolt course up his spine. It was Master Remiel.

'Thuriel, you damned fool,' snarled Sar Daviel. 'You've got no idea what you're playing at here. Tell your men to put away their guns right now, or I'll do it for them.' The old knight's scarred hands clenched into fists. He looked entirely ready to make good his threat.

Daviel's scornful tone brought Lord Thuriel out of his chair. 'Mind your tongue when you're speaking to your betters, you old dog,' he warned. 'Or you'll wind up sharing the same cell as this hyper-muscled monstrosity here.'

'Listen to me,' Sar Daviel said, his voice low and insistent. 'Zahariel is here under the terms of parley. Do you understand what that means?'

'Parley?' Thuriel said with a harsh laugh. 'I've had quite enough of your romantic notions of warfare, Daviel. Do you imagine that Luther has suddenly had a change of heart, and wants to negotiate with us? Use your head, man!' He pointed an accusing finger at Zahariel. 'For all we know, he called this parley to draw us into the open so he could kill us!'

'Shut up, Thuriel,' Lord Remiel snapped. The old master's voice was roughened with age, but still bore the same lash of authority he'd wielded at Aldurukh.

'Have your men put away their weapons before Zahariel decides that the parley is void and turns your paranoid suspicions into reality.'

The noble recoiled from the command as though he'd been slapped. The rebel gunmen wavered, casting uncertain glances between the rebel leaders as if unsure who to follow. When Thuriel didn't respond at once, Lady Alera wormed her way between the gunmen and pushed the muzzles of the plasma guns downward.

'Enough of this madness,' she declared. Then, to Zahariel, she said, 'I regret this misunderstanding has occurred, Sar Zahariel. Lord Thuriel and Lord Malchial acted rashly, and without the sanction of the rest of our leadership. In fact,' she continued, shooting an angry glance at the two noblemen, 'they conspired to delay the rest of us so that we couldn't interfere with their treachery.'

'Now, look here,' Malchial said, rising nervously from his chair. 'I never wanted any part of this. Lord Thuriel said—'

'We've heard more than enough of what Lord Thuriel has to say,' Remiel snapped. 'I advise the both of you to hold your tongue from this point forward. At the moment I'm of the opinion you're a bigger threat to our cause than Luther and his minions, and nothing in the terms of parley prevents me from having the both of you shot.'

Remiel's threat ended the confrontation at a stroke. The gunmen withdrew to stand by the doorway behind the rebel leaders, their weapons held at port arms. Malchial went pale and his mouth snapped shut at once. Thuriel held his tongue as well, though his body trembled with barely-contained rage.

Zahariel observed the entire exchange with outward calm, though inwardly his mind reeled at the implications of the scene playing out before him. It had been obvious from the start that the insurgents were very well-informed about Imperial strategy and tactics, but Luther and General Morten had assumed that deserters from the Jaeger regiments were the cause. The truth, Zahariel now realised, was far worse - and called into question many of their assumptions about the rebels and their motives.

'It was you all along,' Zahariel said, his heart sinking with the realization. 'How many years did you pretend to be our brother while you were laying the groundwork for this rebellion? When did you forsake your oaths to the primarch, master? Did it happen the day that Luther returned from the Crusade - or when Jonson passed you over and chose another to become Lord Cypher?'

'It was Jonson's treachery that brought us all to this,' Remiel said. The old master's voice was sharp as drawn steel. 'An oath born from deceit is no oath at all! His lies—'

'Save your breath, my lord,' Sar Daviel said, resting a hand on Remiel's arm. 'It won't do you any good.' The maimed knight let go of the old master and took a step towards Zahariel, his expression stern and unforgiving. 'You called for a parley, and in honour of the old ways we obliged you. What is it you want?'

With an effort, Zahariel tore his gaze away from Remiel and collected his thoughts. He'd rehearsed this conversation in his head a hundred times on the way to the arcology.

'I'm here because of what you said to Luther, just before you got on the shuttle back at Aldurukh.'

Sar Daviel's one good eye narrowed thoughtfully. He gave Zahriel a searching look, and then sudden comprehension dawned across his scarred face. 'You've seen something, haven't you?'

'What's happened?' Remiel said, a note of concern creeping into his voice.

Zahariel hesitated, knowing that he had reached the point of no return. Luther had forbidden him to discuss the matter with anyone, but if he didn't, Caliban was doomed. Slowly at first, then with gathering speed and determination, he told the rebel leaders what he'd found at Sigma Five-One-Seven.

When he was done, Zahariel studied the faces of each rebel leader in turn. Daviel and Master Remiel cast sidelong glances at one another, their expressions grim. Lady Alera and Lord Malchial were pale with shock, while Lord Thuriel's jaw tightened with building outrage.

'What is he talking about?' Thuriel demanded. 'What's this… this taint he keeps referring to?' He took a step towards the two older knights, his hands clenching into fists. 'How long have you been keeping this from us?'

Daviel glared forbiddingly at the angry noble. 'It's none of your concern, Thuriel,' he growled. 'Believe me. The less you know about this, the better.'

'And now you presume to tell me what I have a right to know? You're no better than the damned Imperials!' Thuriel turned to Lady Alera. 'I told you we couldn't trust them!' he snarled, pointing an accusing finger at the old knights. 'Who knows what other secrets they're hiding? For all we know, they might have been working with Luther all along!'

'Thuriel, will you please just shut up,' Lady Alera said, her voice trembling faintly. She pressed a hand to her forehead, and Zahariel could see that she was struggling to come to grips with what she'd been told. 'Can't you see what's at stake here?'

'Of course I can,' Thuriel snarled. 'In fact, I see things a great deal more clearly than you, Alera. I see that the Terrans aren't content with raping our world; now they're feeding our people to monsters. And these two old fools knew it, but kept it to themselves.'

'We knew nothing of the kind, you arrogant, self-centred dolt,' Daviel shot back. 'Master Remiel and I were protecting our people from monsters long before you were born, and don't you forget it.' He jabbed a gnarled finger at the ruined side of his face. 'You want to talk about monsters, boy, you show me the scars you earned fighting them. Otherwise, shut your damned mouth!'