] I was intrigued by the private chat between Henry and his brother. Shortly after that, Capt. Tilney started paying great attention to Isabella.

I also don't think Henry would have enlisted his brother to draw off Isabella, it would cause too much pain to Catherine.

But, hearing that Isabella was engaged might have piqued Frederick's interest in her. She's spoken for, so there would be no chance of he being obliged to offer for her. I think he can easily see that she is open to a flirtation - I'm sure that is plain to every man there! - and thinks "She's pretty, she's obviously accessible, why not?"

But that conversation Catherine overhears... it is very imcriminating. I think it is flirtation still - has not gone beyond it - but it is Very Serious Flirtation, which I think can easily go beyond just words. He is obviously pressing for more.