This was, simply put, a brilliant book, one of the best I've read.
The alternative reality depicted is captivatingly alike ours, with a small, yet life-altering, twist: somewhere among the billions of people on this earth the other half of your soul is walking around. You might meet them one day, you probably won't, but everyone's cursed to feel incomplete, and that is where Casey Bourne's stories take off: what are your alternatives in such conditions, how can you live with not knowing the other half of your soul, but still have a meaningful life?
Some manage, some don't. Some are raised in the unknown, some go to the ends of the earth just to encounter as many people as possible in order to touch them all until they Bond with their intended Pair.
I want to share one of my favourite lines from the book, expressed by someone who Bonds:
"... From this angle, [he] could find constellations in the freckles on her nose and give names to the individual pigments of her irises if he was afforded the luxury."
It's a beautifully written, entertaining, thoughtful as well as thought-provoking novel, and I highly recommend it.