"You don't know the power of the Dark Side," Vader said, perhaps with some hint of sadness. "I must obey my Master."

"I will not turn-" Luke said, then stopped. "Okay, hold on."

"You have changed your mind?" Vader asked.

"No, but… that sentence had so many problems that I'm going to need to unpack it," Luke replied. "So… firstly, who told you that?"

"It is not merely a thing I have been told," Vader said, ominously. "It is a thing I feel. A thing I know. I cannot go against my Master, I must obey him."

Luke coughed.

"I don't remember this very clearly," he said, holding up his artificial hand. "For reasons which I hope are obvious, father. But I am fairly sure that you offered me the chance that we could rule the galaxy together, as father and son. Was that shock and blood loss, or something you actually said?"

Vader was silent for a moment.

"Yes, it is something I said," he conceded.

"So has the power of the Dark Side changed since then?" Luke asked. "Because what I'm getting at is that if your Master told you that the Dark Side meant that you had to obey him, that sure sounds convenient for him."

"He is the Emperor of the Galaxy," Vader intoned. "Something can be convenient for him because it is true. Things tend to be convenient for him."

"You're speaking to a rebel, father," Luke pointed out. "I know the Emperor is quite capable of lying about things if it would create the impression that things are favourable for him. Did he have to obey his Master?"

"...no," Vader allowed, after a pause. "In fact, he murdered his Master in his sleep, if I understand correctly."

He folded his arms. "And before you ask, no. I cannot do the same to him. I don't think he sleeps."

Luke blinked. "That sounds… unhealthy," he said.

"I know," Vader declared, in sonorous tones. "I know. I once went ninety-six hours without sleep and at the end of it I had fallen to the Dark Side and your mother was dead… in that order, I think. The chronology is somewhat indistinct."

He made a slight gesture. "The Emperor is either not so prone to the weaknesses of the flesh, or he legitimately does not care. Or I have simply been unable to determine when he sleeps, which is the same for these purposes."

Luke nodded, slightly, then frowned.

"...just so I am clear, father?" he said. "You want me to turn to the Dark Side? Because what you're saying about needing to obey your master sounds like a good reason to not turn to the Dark Side. It completely destroys all the most tempting arguments, especially since the Master in question is an enormous bastard, and the fact that you also just said you turned to the Dark Side when your judgement was seriously impaired-"

He cut himself off.

"You take my point, I hope?" he resumed. "I don't want to be in a situation where I must obey the Emperor. You're making it sound like it's not a matter of choice, and that I have to obey him even if I don't want to do the specific thing or even in general want to obey him."

"It is too late for me," Vader said. "I am a prisoner of decisions made long ago. I cannot be saved."

"You are a prisoner of your belief that you're a prisoner, and the only thing making it so you can't be saved is your belief that you can't be saved, but I had another point to make," Luke replied. "Which is… literally, no you don't."

"...elaborate," Vader said, after a few seconds. "I fail to understand the point you are attempting to make."

"Excuse you, I'm making it quite well," Luke replied. "You said – I must obey my Master. And I'm saying – literally, no you don't."

"You do not understand," Vader said.

"Then explain it to me," Luke requested. "What, physically, would happen if you just came with me and walked into the woods?"

For almost thirty seconds, there was no sound but the hiss of Vader's respirator.

"...I actually don't know?" Vader said. "But it is impossible."

Luke sighed, rubbing his temples.

"I've been on both sides of saying that," he said. "That something's impossible. It's not impossible. Hitting the Death Star's weak spot without a computer – that's impossible. Using the Force to lift an X-Wing – that's impossible. I did the one I didn't think was impossible, and I saw the one I thought was impossible done – in front of my eyes."

He looked up at his father. "Find a better explanation, or tell me that you want to obey your Master. Don't hide behind must if you can't explain what the word means in this context."

"I have come to a conclusion," Vader said, firmly. "You were definitely trained by Kenobi."

AN:

Negotiator II, the Negotiating