The Doctor froze. "A new mind"? So what about...
"That's the best part; they're gone. Vanished. Eradicated. Exorcised. Poof. For the first time in a long time, I'm me again, Doctor."
A stunned silence filled the air. Then the Doctor grinned. It wasn't manic, it wasn't triumphant, it wasn't even a mask to hide behind; he was beaming in pure unadulterated joy, something the Master hadn't seen on his face in centuries.
"Master, that's fantastic! You can come with me! You're free! You're alive! You're-"
"Joking." Jack's voice cut through the Doctor's good mood like a knife. The two Time Lords turned to him, startled, having for a moment completely forgotten he was there (a difficult task, considering that their species had a natural aversion so strong to Facts like him that even the Doctor flinched sometimes). "Doctor, from what you've told me about those drums they're supposedly what made him like this. Now we're going to let him go just because he says they went away? He's a psychopath! What about everything he ever did to you, to the world, to the universe? What if he's lying? You've never been able to hear them before, so if he was there'd be no way to find out until it was too late! By the time we know for sure he could have wiped out entire civilizations on dozens of planets. He's a monster, and at the very least he needs to pay for what he's done. I'm sorry Doctor, but he's not going anywhere."
Jack finished his rant with his eyes screwed shut. He opened them to the sight of a very hurt, very sad, and very, very angry Doctor glaring at him. Guiltily he shifted his gaze away and saw the Master. Every hint of laughter was gone from his face, replaced by what seemed to be... acceptance.
"Jack." The Doctor's usually soft voice was brimming with fury. The Captain cringed at the tone, expecting a rather passionate sermon about needing to move on and forgive others.
What he didn't expect was a punch to the face that would throw him off his feet. Jack laid on the tiled floor panting and rubbing his jaw while the enraged Time Lord towered over him. The Doctor bent down and picked Jack up by the scruff of the neck, then slammed him into the adjacent wall. His eyes were filled with anguish, and the primal glint that came from protecting one's own. Still holding Harkness' limp body to the wall, the Doctor raised his fist, prepared to strike again.
The pleading cry came not from the immortal man in front of him, but from behind. The Doctor stopped and blinked. His expression cleared, and he stared at his arm, still frozen mid-swing. With a look of unmasked terror he dropped Jack and quickly stepped back, horrified at what he'd been about to do to one of his most faithful friends. Jack shakily got up and looked around, meaning to thank whoever had saved him from the Time Lord's wrath- but they were alone. Just him, the Doctor... and the Master.
The Doctor followed Jack's gaze and rested his eyes on the cell behind him. There was the Master, looking neither pleased nor satisfied, with his face shoved closely to the glass. He seemed desperate, scared even, and he took a deep breath to calm himself once he knew the Doctor was back to his senses. He looked shaken, but the Master's voice was firm.
"He's right, Doctor. About everything. The drums controlled me for so long, I forgot what it was like to feel, well, anything really. Regret, remorse, guilt, sadness... I lost it all. I became exactly what he said I was; a monster. These emotions- I haven't felt anything like them in nearly nine-hundred years. I killed so many people, Doctor. So many innocent people we can never save, that I can never apologize to. I deserve this."
The Doctor's face softened, and even Jack felt a bit sorry for what he'd said.
"No you don't. You obviously know what you did was wrong, there's nothing else you can do. Apologizing to whoever you left behind won't help, it'll only open old wounds and make things worse. Come with me; we'll leave everything for a while, just the two of us. It'll be just like what we dreamed about back on Gallifrey, eh? You and me, the whole of time and space, just waiting for us to see it. A few months away from it all to just get used to it, maybe a couple of planets, nothing to hurt or hurt you; how does that sound?"
The corners of the Master's mouth twitched. "Boring", he said, "but I'm sure you'll keep me entertained somehow."
Jack sighed; this was obviously a battle he wasn't going to win. He pressed a button on his communicator and held it to his mouth. "Ianto, Gwen, stand down. He's leaving in the Doctor's custody, repeat, the Master is leaving in the Doctor's custody." He looked up at the Doctor, who smiled in gratitude and shame.
"Thank you, Jack. And I really am sorry about the punch."
Jack nodded, then looked the Time Lord in the eye and saluted. "Don't take your eye off him, Doctor. I'm counting on you."
He turned around and proceeded down the hallway back the way he'd come while Jack unlocked the Master's cell, and with a little electronic beep the door swung open. He grinned at Jack as he left, then followed the Doctor down the hall back to the Tardis, Jack close behind. The blue doors shut with a snap of the Doctor's fingers, and a moment later the blue box and her passengers were gone.