Vader frowned slightly, the reaction concealed by the mask he had hidden behind for so long. It was a strange question... for so many reasons. Palpatine never referred to Luke as Vader's son- not to his face. Nor had he ever asked this directly before... and why ask at all, if he believed he knew Vader's every move?
"No Master." Vader stated simply, rising as he did so. It was, strictly speaking, true.
The Emperor only nodded, his back still to Vader, "He is... difficult to read. To predict. To control."
Vader remained still, uncertain what his Master wanted of him.
The Emperor turned slowly, hands tucked into the voluminous sleeves of his gown, "But I think that the error is partly mine. You see, he cannot be controlled too closely; pull the leash too tight and he begins to resist. Of course some things can only be learned with hindsight, but I now believe... I believe in order to control him one must instead control his surroundings; his connections. My error was in not realising that sooner- but knowing it now, I will correct it."
Vader was still, the uneasy twist of menace that had coiled about him now shivering up his spine, tensing muscles.
Silence hung expectant in the still air as the Emperor paused, pale, ochre eyes lost in consideration.
"Do you remember the Prophesy, my friend- The Son of Suns?" Palpatine set his head to one side in contemplation, "Prophesies and visions are such vague things; they have so many interpretations."
He finally turned to Vader, yellow eyes aglow, "Do you feel you have balanced the Force? You certainly evened the score; created symmetry- in retrospect only four of us remained for a long time; two Jedi and two Sith..."
"The Force was in balance- it had not been so for many decades." Vader said neutrally, uncertain of his Master's itinerary.
"Yes..." Palpatine smiled at Vader's interpretation; he had always been so literal, content never to look beyond the obvious. "But I always believed the Prophesy was something more - it stood for so long; surely it could not be as simple as that."
Palpatine paused, eyes hooded beneath that heavy, disfigured brow as he considered, "It is shadows whose edge define the light, at the brink of the dawn and the Darkness." He quoted from the prophesy, "Light and darkness... one cannot exist without the other. Light, by its very existence, creates shadows, and it is darkness which defines the existence of light. And yet we separate them so completely... believe them incompatible ... irreconcilable. Perhaps they were..."
The realisation of what Palpatine was suggesting came to Vader in a burst of comprehension- of Luke, of how much remained carefully hidden. Of his nebulous, indefinable sense within the Force - of the moment long ago in the Medicentre when, racked with pain and appallingly injured, his son had reached unthinkingly into the Force for healing- and accomplished it.
But Darkness did not heal. Darkness could not heal.
He remembered sensing that fleeting glimpse beneath the boy's shields, that particular mindset; the willingness to merge without loss of self, to surrender without submission into the Force. Darkness never surrendered... so it was not this that the boy had touched, yet... he recalled again that momentary contact, searching to categorise it as it had slipped away, diffuse and veiled.
It was not Light, nor was it Darkness - it was... both and neither, defying classification.
Palpatine had always told Vader that he was created by the Force- brought into existence by it... by the power and the will of Darkness, his Master claimed... so how could Vader's connection be anything more? Intense as it was, how could it be more?
But hadn't Vader said... He'd told the boy so often, yet never listened to his own words- that Luke was the sum of both himself... and Padmé.
And Padmé was nothing but Light...
Could their son contain both aspects of the Force? Was it possible for one being to hold the two in balance?
Had Vader created that which fulfilled the Prophesy - the balance of Light and Darkness...
Palpatine had turned slowly away to stare out across the metropolis once more, that tense stillness cloaking him, true intent hidden beneath darkness and shadows.
"You have served me well, lord Vader..." Palpatine nodded, thin lips pulled back into an empty smile, "But I should have recognised that your work was done the day that your son arrived here. Your usefulness at an end. I should have seen... realised that balance of Light and Darkness which you brought to me is the fulfilment of the Prophesy - ultimate power - because whoever controls it truly commands all aspects of the Force."
The Emperor nodded, speaking as much to himself as to his acolyte, voicing aloud his conclusions, grating tone low and emotionless, "Whoever controls the boy commands everything - elemental power in all its aspects - and I can never truly do that whilst you are alive. He will always look to you, I see that now. And I will correct it."
Vader saw the glint, the slightest reflection of sunlight on metal as Palpatine unfolded his arms, and knew what was in his Master's hand.
But then, hadn't he always known that it would come to this? Only not quite like this. He'd always thought it would be some bitter, incensed fury, some mindless frenzy of rage and wrath which brought him to this point. Not this... this peerless honour, this ultimate accolade - proof undeniable that his son looked to him, respected him... valued him. He himself, not his ability; that was nothing to the boy. And to know this, to know it absolutely, to hear it spoken by one who would never give such recognition lightly, finally gifted Vader the realisation of what that connection meant to him...
Not the awareness of what Luke was; his power or his potential, nor the fulfilment of the Prophesy which Vader had dragged like chains about him his whole life... but realisation that his son loved him- that this bond was so deep that nothing Palpatine ever did could eradicate it; nothing. Because it was a part of Luke... as it was a part of Vader.
The knowledge... was like sunlight on bare skin, warming him through to the depths of his soul. And he hadn't felt that for a lifetime.
And now, finally he knew what had held Luke in check... knew why the boy would never take that final step. It wasn't himself his son was protecting - it was Vader. Hadn't Luke said as much when he'd been injured - the very first time he'd spoken to his father about ousting Palpatine - hadn't he said even then that if he came to power, it would put him in direct contention with his father.
And his actions with Palpatine; always wavering between uneasy capitulation and stubborn defiance regardless of the consequences, always unstable, always unpredictable. Just enough that Palpatine wouldn't yet risk removing Vader.
Did he know- did the Emperor comprehend just how much sway he held over the boy in Vader?
Because here - here was the answer. To everything. Palpatine had no concept of just how deep the connection between father and son ran- how could he? He knew only lies and manipulation; the concept of sacrifice was beyond him. Selflessness; compassion. For all his reliance on soulless technology to keep him alive, Vader felt in that moment that he had more humanity within him than his Master could ever hope to perceive.
Which was why Palpatine would never realize...
Vader felt some pang of guilt at taking this decision from his son; in knowing that his actions now would force Luke's hand. But whilst he was alive his son will always seek to protect him; by Luke's own choice, he would never come to power whilst Vader was alive.
Any price, Vader recalled; any price to free his son's hands... they weren't empty words.
This was his chance at reprieve; to atone for his own blind ambition, which had dragged his son centre-stage. It had been Vader's choice to set him on this path... or perhaps it had been Obi-Wan's, for he surely knew that if he trained the boy, then Luke would be instrumental in the turning of the Fates one way or another.