Time-Flown

Good heavens, it's the Master! Whoever would have guessed it?! Certainly not the Doctor, who has a splendid blind spot where his old sparring partner is concerned. Either the Master has taken the opportunity at some point to hypnotise him into being unable to see through his disguises, or the Doctor sees through them immediately, and plays along with the charade through sheer exasperation.

( Etc... )