At what point did I know Percy was the SP? Maybe I'm slow, but I didn't even really suspect Percy until he was the only one in the dining room, sleeping. But after that I pretty much knew for sure, though I thought Marguerite was pretty slow on the uptake!
I have a different opinion than Ranee on the second question. I think that Marguerite was pretty justified in her actions, I think she was appropriately torn up about it. She was put in an impossible position. And if you are choosing between the life of your brother and the life of a stranger, I think it would be difficult to choose the stranger. She also knew for sure that her brother would die if she did nothing, but had the hope that the SP would somehow be able to escape considering his cunning. I think that Percy knew about the betrayal because he talked to Sir Andrew, I'm guessing he filled him in. Or maybe the SP is just so all knowing, he figured it out all on his own. :) I think that Marguerite proved herself by the lengths she went to to try and warn Percy, and the fact that even if she couldn't save him she wanted to die next to him, as long as she could tell him she truly loved him. That's good enough for me! :)
I enjoyed this book a lot, and look forward to continued discussion about it!