The Master wanders the wasteland, staring around, sniffing something. He throws back his hood; the Doctor can smell him, in return. The Master is overjoyed, manic, and begins to beat upon a metal barrel with a huge pipe. Guess how many times?
The Doctor finally locates him, drawn by the drumbeats, and they chase each other for so long they end up with their places reversed. The Doctor stares up at him, lovingly and terrified, and finally the Master explodes into space again, landing and running; he laughs, buzzing into a death's-head once again, and the Doctor begs to let him help. The Master rolls his eyes, charmingly, and sets off again. "You're burning up your own life force!"
NINE: A Kiss
Wilf intercepts the Doctor, relieved and excited to see him, nearly weeping with joy. The Doctor is torn, between tracking down the Master and letting himself be happy to see Wilf. Finally he gives in, as the Silver Cloak tells him how exactly they triangulated his location, and before he can do anything they've clustered around him, touching and grinning. One old queen snaps a picture of him with Minnie as she grabs his ass. The Master is long gone.
Later the bus drops the Doctor and Wilf at a pub -- Minnie blows him a kiss, outrageously -- and Wilf leads him inside, refusing to tell the Doctor what's so special about it. At the table, Wilf reminisces with the Doctor about their good times -- the Atmos system, the Stolen Earth, the paint gun -- and finally, through a fake laugh, admits he's terrified. He admits seeing the terrified face, in his dreams, and remembering them. The Doctor stares at him, puzzled, wondering how Wilf's always been able to find him so quickly, and shakes his head: "We keep on meeting, Wilf. Over and over again. Like something's still connecting us." Wilf wonders if it's important, if he's important, but the Doctor doesn't know. All he knows is that he's lonely.
And so, surprising himself, he gives it up suddenly: "I'm going to die."
Wilf says he's going to kick one day too -- "Don't you dare," the Doctor snaps lovingly -- and watches his Doctor, grown sad and alone. "I was told 'He will knock four times.' That was the prophecy. Knock four times, and then..."