Really love the playfulness (and ultimately the grinning refusal to give us a set answer) of just how much and what the Doctor suspected about Turlough prior to Enlightenment. The Fifth Doctor is a much more competently crafty character than a lot of vocal fan wisdom decries, and bits like this really illustrate the influence he had on some EDAs takes on the Eighth.
Turlough’s face at the end there says it all, really. He KNOWS that Five knows, but neither of them say anything.
And the added hilarity of Alistair standing in the middle of that KNOWING that Turlough KNOWS that Five Knows. But he has no idea WHAT they all Know.
Alistair trying to figure what it is that Turlough knows The Doctor knows, what it is The Doctor knows that Turlough knows, what it is that they seem to know that he doesn’t know, and what it is that they’re pretending the other person doesn’t know they know