Minor typo at the end of 78, repeated at the beginning of 79:

The Aurors swept toward him with swift strides, Auror Goryanof approaching from the other side of the Ravenclaw as though to block any escape...

Actual speculation: what did Dumbledore know or suspect when he hired Quirrell?

"If you consult Headmaster Dumbledore," said the Defense Professor, "you will find that he is well aware of this matter, and that I agreed to teach his Defense class on the explicit condition that no inquiry be made into my -"

What exactly was Dumbledore aware of? Merely that 'Quirrell' may have travelled without a visa (I guess this is illegal), or that he was an impostor? If the latter, why would Dumbledore hire him?

But if Dumbledore wasn't aware that Quirrell is an impostor, then Quirrell has made at least one foolish slip. During the interrogation, Scrimgeour says

"Born the 26th of September, 1955, to Quondia Quirrell, of an acknowledged tryst with Lirinus Lumblung..." intoned the Auror. "Sorted into Ravenclaw...

But way back in Chapter 16, Quirrell says

Yes, I was in Slytherin and I am offering to formulate a cunning plot on your behalf, if that is what it takes to accomplish your desire.