Mediocre for me. 
 two things I didn't like about this book: I found Leo's character underdeveloped, despite promising further development and conflict. I think the relationship between him and Jason ( the rivalry, the spotlight) could have been further elaborated on, and this problem should have been solved in the first book, and not left to the other volumes. 
 Also, I felt that Leo's character was one that just asked the obvious questions which the author could use as a follow-up for the next surprise, or twist to the story. Which for me, was quite unnecessary, for i felt that mere explanation from the characters producing the surprise to the story should have sufficed. The plot being rather predictable (for me) didn't help either. I think this made Leo's character seem impulsive, or rash, and not much of a thinker. 
 I didn't like the chemistry between the two main characters either. Had I were Piper and had known about the false memories implanted in me about jason, I wouldn't have been any more desperate and hopeful about anything romance further developing. Instead of building a new, budding relationship, what Piper dwells on is her memory, which has already been proved false, and intends to continue from there, which i find completely absurd. A large portion of the book focuses on this thought of Piper's, though I don't see any problem of building the relationship from scratch. Because of this, Leo is also sidelined. A pity really, as I felt Leo's insecurity towards his powers, social life, and past really really promising. 
 Overall, lots of action, nice plot, but mostly unpolished and perfected.