[Mentalis the computer advises the Doctor through K-9 that the next step in the war between Atrios and Zeos is obliteration of everything]
Doctor: Has it ever occurred to you, Shapp that you and the Marshall and this thing [speaking of Mentalis] are in an arena playing out a game for some evil alien spectator?
Romana: The third force?
Doctor: Yes, I think I’ve met him. Calls himself the Shadow.