Vader lands on the Executor with the Emperor's chosen spy: a pompous, newly promoted officer who thinks that simply because he can flounder through Vader's private files that he is somehow important.
Vader will enjoy watching him die.
As soon as he is clear of the docking bay, Vader finds himself striding towards the detention deck on instinct, instead of making a line straight for his meditation chamber as he usually does. The entirety of his time spent on Coruscant, as well as the hyperspace leap back to his flagship, had been spent dwelling on Obi-Wan, as well as the mysterious Rebel pilot. He feels that if he doesn't manage to investigate one or the other, he is liable to explode.
And since Obi-Wan is more readily accessible (and unknowingly tugging at Vader's Force signature since the moment Sith Lord disembarked) Vader goes to him first.
He really wishes he hadn't.
As soon as the cell door slides open, he very nearly kills the man.
Because this Obi-Wan looks so much like his old mentor had. In the weeks Vader had been gone, he'd managed to a grow a scruff. Not quite the beard Kenobi had prided himself upon, but near enough that for a moment, a split second of pure agony, Vader is twenty years in the past. On Mustafar, bleeding, burned, broken, snarling after the man as Kenobi clears the black hill and doesn't look back leaves him to die alone and screaming-
He's pulled out of his reverie by this Obi-Wan mentally short-circuiting his aural implants with desperate cries for his apprentice.
Anakin, where are you? Anakin, answer me! Anakin, please...Anakin, are you alright?...Anakin...Ani...
The voice throbs in his head, and Vader bites out, "I can sense you attempting to contact your apprentice. Cease."
Obi-Wan's mouth thins and Vader senses the considerable mental shields in his mind building even higher. The fool. He has no clue that he has given Vader easy access to his mind, by keeping the link with his apprentice open. Vader simply chooses not to follow along it, because a bond such as that works both ways. No, he definitely does not need that.
"Sith," Obi-Wan straightens up, staring Vader's chest-plate down with a near-perfect scowl. "I demand you tell me where Anakin is."
Vader says nothing, letting his respirator fill the silence until Obi-Wan finally squeezes his eyes shut and snaps, "Lord Vader, will you please tell me where my apprentice is being kept?"
Vader ignores the question, watching the worry and apprehension play themselves across the younger man's face, and suddenly Vader has the urge to be in control of him. To have Obi-Wan answering to him, following after him like his life depends upon it, never ever leaving his side again.
It is such an intense feeling that even Obi-Wan glances up at him in confusion, taking a step back at the sudden wash of unwarranted possessiveness flooding over him.
"What in the hells..." Obi-Wan mutters, bolstering up his shields even further, until it seems to cause him physical distress. "Vader?"
"Henceforth, you shall call me 'Master'." Vader replies, coldly.
The glare Obi-Wan gives him shows that he would much rather run the Dark Lord through with a lightsaber.
Vader gives a wild guess as to why. This version of the man is still rather young, after all.
"I will not be replacing Qui-Gon Jinn." Vader says, and, truthfully, he has no desire to. Jinn had been a Jedi worthy of his respect - one that understood the inherent weaknesses of the Order, and who had defied them to allow Anakin Skywalker to be taught.
Obi-Wan grimaces at him, and there is a deep wound there. One that has yet to scar over completely.
That may prove most useful to Vader.
"Don't you dare say his name, Sith," Obi-Wan growls, low. "I will never call you or your like 'Master'."
Vader crosses his arms. "Then the one that calls you such will die. Horribly." He reminds him.
Obi-Wan's rage is slowly replaced with a mollified expression. It is nearly pathetic enough to make Vader feel guilty about lying to him. Nearly.
"I apologise...Master." Obi-Wan says, quietly.