"Why are you doing this?" The Doctor asked, barely able to lift his head. His lip was split in too many places to count, from where he had been punched, again and again, all he could taste and all he remembered tasting for a long time was blood, he had bruises around his neck at varying stages of healing from where he had been strangled, his stomach had been used as a punching bag, he had two black eyes from days ago, when his captor had gotten particularly mad, and he was hanging from the roof, causing angry red marks to show on his wrists, and sometimes he would struggle so much it would draw blood.
The Master looked down on his former friend. He just looked pathetic now. He leaned down to whisper in his ear, an evil smile on his lips. "Because I want to." The Master turned away, his back facing the Doctor. "Have you ever felt the pleasure of torturing someone, Doctor? Having their life in your hands? Being able to put them out of their misery at any time? It's exhilarating." He leaned over a table that the Doctor had long ago discovered held his 'tools.' The Master chose one that looked suspiciously like a cattle prod and studied it. Nodding in confirmation at his choice, he slowly walked back towards the Doctor until they were face to face.
The Doctor's eyes went wide and he began to strain against his shackles, but it was no use. The Master smiled and stroked the Doctor's cheek, down his neck and across his now bloody and scared chest. The Doctor's heart sank, when the Master touched him like that, he knew the worst was yet to come. It was always that way. So for the moment he closed his eyes so that for an instant and he could almost pretend that they were young again, back on Gallifrey.
At least until the searing pain started spreading from the cattle prod all through his body, and all that could be heard for hours after was the Doctor crying out in agony.