The five stars are for Hero Jarvis, whose name really fits the bill. I liked Kat well enough, but Hero really impressed the pants off me. I love her strength and determination as much as I love her imperiously stiff upper-lip. I read her as a character with the bearing of an Amazon queen and the buttoned-up appearance of a librarian, and that is a fascinating combination. If more female characters had the stuff Hero Jarvis is made of, we'd be wading through a lot less crap.
I know that Kat is the great love of Devlin's life, but for some reason they were always rather bland to me--possibly because the book starts off with their relationship more or less established and oh man these stars how they are crossed--but I think there's a great deal of potential chemistry between Devlin and Hero. Her relationship with her father Jarvis is also very interesting to me -- man is he going to blow a gasket if this story goes the way I think it's going.
Oh right, and other things happened. Hero really stole the spotlight in this one.