VALEYARD: There's nothing you can do to prevent the catharsis of spurious morality.

DOCTOR: In all my travellings throughout the universe I have battled against evil, against power-mad conspirators. I should have stayed here. The oldest civilisation, decadent, degenerate and rotten to the core. Ha! Power-mad conspirators, Daleks, Sontarans, Cybermen, they're still in the nursery compared to us. Ten million years of absolute power, that's what it takes to be really corrupt.