[SPOILER FREE]
Ana. DI. Robb. Jax. 
These characters have coveted my heart until the end of time.
Ashley is a prime example of an author who puts her characters through hell and back. I can't even list out all the times she made them suffer!
DI stole my heart the most in all honesty. Throughout the entire book I just kept feeing my heart melt whenever he was either with Ana or trying to help her in the best possible way. He reminds me so much of Iko, but I think that's because they're both androids- though he just is too precious for this world! I really just need to hug him right now, and also I need to have a conversation with Ashley about him because W.H.Y.
I'm trying very hard to not spoil you guys at all because all I want to do is rant about how amazing this story was, but I can't since that would involve spoilers.
Though I'll just say it now: I'd recommend you know nothing going into this book. 
I mean the ultimate plot twist of the story happened, and I was left in a state somewhere between shock/ horror/ revulsion. 
It has been so long since I've enjoyed a sci-fi book to this degree, and I can't thank Ashley Poston enough for that.
The character relationships are probably my favorite part besides the writing/ jokes. Jax's sass and jokes are the essence of this story as much as Ana and DI's friendship.
Then my heart has to go and burst because of that ending. I just HAVE to mention the ending because W.H.Y.
Heart of Iron is in my top three favorite books of the year, and I'm begging all of you to read it once it is released February 27, 2018. I certainly was not disappointed in the slightest by this beautiful, heart wrenching story, and I hope you guys are just as fascinated.
This squad of four took me on a journey I'll never gonna forget.
ALSO I NEED THE SEQUEL- ASHLEY I HAVE TO KNOW WHAT HAPPENS AFTER THAT ENDING. 
MY. HEART. IS. IN. PIECES. ON. THE. GROUND.

Edit: Since it's been years and I haven't picked up the sequel (nor have any inkling), I'm going to lower this rating.