Callum was a superb secondary character and love interest. He brought out the character development with Wren and it was great how his smile and the fact that he retained so much of his humanity highlighted the personality and emotions of Wren that she'd previously buried.
I really enjoyed being in Wren's head. She was tough, and I got to see her humanity come out and see her make her own decisions through her interactions with Callum and her friend and roomie Ever.
There was a great mix of action and character building, and I was glued to the pages and essentially finished in one sitting on the train back from Boston. I was thankful for the lack of interruptions.
Some might be frustrated that the romance and building of it almost takes front seat to the robot elements, but for me felt just right. I think that Wren has reservations and that she had a hard time breaking free from the expectations on her, and Callum influenced that change in her a lot. But he wasn't the only one and for that I am grateful. The experiments and differences between Wren and Ever also shepherds some of this change.
The plot of this book tied up pretty well, giving me the right balance of closure and yearning for the next book to find out what happens next.
Bottom Line: Devoured it!