"They took me there. In the dark. I looked into time, old man. And I heard it. Calling to me. Drums... The never-ending drums."
He looks very young. And very sad.
"The Untempered Schism," Rassilon spits. "That's when it began." That's where it always begins. "History says the Master heard a rhythm. A torment that stayed with him for the rest of his life." A drumbeat. A warrior's march. A symptom of insanity, like all war. The Visionary taps, again and again, with writing all over her skin: A rhythm of four. Rassilon leans forward, in his hate and his madness.
"The heartbeat of a Time Lord."
The Master is lost. He leans back in his chair, listening to it, glorying in it. The Doctor offers to go with him, to go and find it, and that sets the Master off. He stands, ecstatic; his brilliant mind burning beneath his skull. "The noise exists within my head. And now within six billion heads. Everyone on Earth can hear it. Imagine... Oh!" He shudders again, a skeleton, and the Doctor worries at him: He's still dying.
"This body was born out of death. All it can do is die. But what did you say to me, back in the wasteland? You said the end of time."
The Doctor corrects him: "I said something is returning." The Master wonders if that wasn't him, after all, in a different way: "The drumbeat is calling from so far away. From the end of time itself. And now it's been amplified six billion times. Triangulate all those signals, I could find its source! Oh Doctor. That's what your prophecy was. Me!" He slaps him again, terrifying, and starts in about the TARDIS again. The Doctor mourns; how close they came, for a moment.
"Just stop, just think," the Doctor begs, as the Master tells himselves to kill Wilf. "Tell me where it is, or the old man is dead." Wilf begs him not to do it, offers to die himself, but the Doctor grins back: One of the guards is the Vinvocci scientist in disguise. Which is funny, because the whole point of having them in SWAT masks was silly and budgetary, but manages now to be essential. The scientist knocks him out, and Wilf yells, "God bless the cactuses," which is totally racist, and then they're off. They can't unbuckle him from the Hannibal Lecter contraption, so -- while the other Masters scrabble and try to find them -- this merry band, the Doctor and Wilf and the two cactus people, have a mad dash around the castle and back downstairs, but before he can stop them, they've teleported all four back to their salvage spaceship, leaving the TARDIS far below.