Really, what is there to be said about The Fiery Heart that hasn't been already? Not only is it right in the middle of the series - which is hard to review on any given day - but the love I have for this series has soared. 
 I want to point out that although I gave The Indigo Spell 4- stars, it was my least favorite book in the series. Why? I felt the whole plot - especially Marcus - was anticlimactic. I say this because I held off reading The Fiery Heart upon its release because, well, I was disappointed. But with book 6 coming out right around the corner, I felt the need to pick these back up. 
 Whereas The Indigo Spell was what I called "Sydney's book" The Fiery Heart is Sydney and Adrian's book. The whole series has been a slow build up to their relationship, and I loved that we finally get to SEE them together. I am just in love with this couple. (So much more love than Rose and Dimitri.) This book has a heavy focus on their relationship and I loved it. Their chemistry is off the charts (especially for a YA book) and their love just makes me ache... In a good way. 
 That's not to say that there was nothing PLOT wise going on. The main focus is working on these tattoos that will counteract with the alchemist compulsion in their tattoos; and the possibility to protect others from going Strigoi. A lot of the questions I had leading up to this point have been answered. And it's really interesting how this all works, too. 
 Another thing I loved? We have Adrian's POV. I found it odd at first that his POV was being introduced in the 4th book, but considering the direction the series is going and what happened here in The Fiery Heart, it was necessary and welcomed. I loved being inside his head. Adrian's mind has always been a mystery to me. 
 Two other small things I must note - I loved that Mead didn't hold back on sex. Was it detailed? No. But usually in YA, sex is skimmed over and isn't (really) talked about. Their conversations were open about birth control, her reservations about sex and then afterword, when they were having sex. Kudos. 
 Zoe. I detest this girl with a fiery passion. Even before the ending when she really showed her true colors, I couldn't stand how selfish she was. She is a BRAT. (Another B word came to mind, but....) 
 The ending? *THROWS ALL THE THINGS* 
 Overall - I loved The Fiery Heart. This book was the turning point for me in the series. I highly recommend you read it ASAP, or start this series if you haven't yet.