"Just… Listen."
And in the moment they shared so much more than just his drumbeats. For the first time in so long they were entwined, as Time Lords should be, and their brains cried out for so much more. Neither of them was lonely. Their own existences were made that much more real by the fact that the other was there. The Master reveled in the Doctor's brain, which allowed him to enter for the first time in so many years. It had been too many lonely years since their minds had touched, and in that one split second they shared everything.
For that single moment there was no feud between them, they weren't kneeling in a junkyard. They were back on his father's land, sitting together in the red grass and watching as the sunset made the spires of Gallifrey look like they were burning with the intensity of the light that illuminated them from behind.
And in that moment, The Master offered his entire self up to the Doctor. He begged the Doctor to understand his drums, to help him, to fix him. He stripped himself down to the core of his being. For just a second he was Koschei again. For just a second he swore his drums were gone, and he felt like crying from relief.
And then the Doctor jerked back, as if afraid of the contact. The moment was over. Koschei was the Master again. And the drums were back, made all the more horrible thanks to that one beautiful second of peace in his mind.
