Madness. It was something the Doctor was well acquainted with. With each regeneration, his own seemed to grow stronger, fueled by his own darkness and self-loathing. I was why the Master was so horrifying, why the Rani's experiments disgusted him so.
The Doctor sighed, staring at his sonic, so different from his predecessor's. Big, bulky with a green light replacing blue. But the light wasn't what haunted his mind, no it was the feel, the very design and color scheme of the tool. It reminded him far too much of…
But he couldn't dwell on such dark thoughts, not while alone as he was. He shook his head, landing the TARDIS. Eyes widened at the image in the monitor and the Doctor gave the ship an incredulous look. "Are you sure about this, old girl? Even after..?" She rumbled as an answer. "Alright. Okay, I'll talk to him."
The Doctor opened the door, smiling sadly at the man facing him. A smirk graced his longest friend's face, confusion and delight warring in the Master's eyes. "Doctor. New look, is it?"
"Hello old friend." He looked around the office, rather bland for the Master. "How long since the end of the universe?"
"Six months." The Master rose, moving next to the other. "So nice to see you're still avoiding death. Mostly." His piercing eyes rested on the Doctor's face. "What number are you on now?"
The Doctor laughed. "I didn't come here to discuss age with you, Master. Not really, anyway." He blocked the gentle mental prod, sending back a scolding look.
The Master glared, annoyed. "Then why are you here, dear Doctor?"
Staring out the window, the Doctor hesitated. Finally, "D'you have your laser screwdriver yet?" He asked. The other Time Lord nodded, fishing the gold and white device out of his coat. "Take a look at this, then." The Master caught the sonic, appraising it critically before looking over his own device. Bright eyes flickered up to study the Doctor. "What do you see, Master?"
"It's finally caught up with you, hasn't it? The insanity of isolation? Oh, sure your little pets help a little but you're mind, you here no one but yourself and it's driving you insane. This," he leapt back on subject, holding the Doctor's screwdriver, "has a laser setting. And it bears a striking resemblance to my own." The Master closed the short distance between the two, their heads rested upon each other's, listening. Listening to the ambient noise of the mind.
A steady four beat vs a frantic buzz, cold insanity against burning madness. Clear intention and steel walls. With great effort, the two disentangled minds, the Master's eyes glazed over. Smiling sadly at his friend for the last time, the Doctor turned toward the TARDIS, sonic back in hand.
"Don't worry, old friend." He murmured softly to the Master. "You won't remember any of this."