Chain Reaction is the final book in the Perfect Chemistry series and it follows the baby brother, Luis, as he gets readjusted to the Chicago suburb that was introduced in Perfect Chemistry. It also follows Nikki Cruz, a girl of Latino heritage, but who lives on the "white and rich" part of town. This is the story of how despite all odds, Luis and Nikki can be together if that's what they want.
I think it goes without saying that Simone Elkeles knows how to make a good love story - especially the "forbidden" kind. But I think what I really liked about this book was Nikki. She wasn't some goody goody girl who was shy or quiet; she was assertive and she wasn't perfect. She is what really made the book for me.
This isn't my favorite in the series (that honor belongs to Rules of Attraction) and I didn't necessarily like the "twist" at the end, but I'm glad I read it because I really needed the closure to the story of the Fuentes brothers that it provides.
If you've read the other two books, you definitely want to pick this one up.