We watch "Utopia" (Series 3, Episode 11) where the Doctor and Not-Rose travel to the year 100 Trillion with a hitch-hiking Captain Jack. Whilst there, they encounter the last of humankind, avoid dining with cannibals and meet Professor Yana. But the kindly Professor turns out to be a masquerading acquaintance of the Doctor's. An eeevil Timelord known as the Master. He's like the Moriarty to the Doctor's Holmes. Or like Puddy Tat to Tweety Bird. Or like Radiohead to Lana Del Rey. Or like... you get the picture.