Tia's abilities are a little odd, even for this series. Her main one is pretty much spelled out in the title: she can make herself invisiable - or at least manitulate the energy around her to make people not see her. Most of her childhood was spent in an instution - one that many assumed was meant to make her (and the others) "normal", but was really expermenting on them. Everything that happens in this book seems to tie back to the lab she spent most of her life in (her parents sent her there when she was ten, but I'm not sure how old she is during this book.)
Tia and Dean seemed strangely perfect for each other, although they did seem a little rushed to me, but that seems common when someone is after one or both of the people in the couple. I can't say I was really rooting for them, but like I said it seemed a little fast.
I enjoyed this one but it isn't my favorite in this series.