I adored this book. It's set in an alternate future in which the USA has illegalized abortion but instead given parents the option to have their children "unwound" between the ages of..14 and 18, I think? Unwinding is basically live organ donation; every part of the unwound child must be given to another person so that, in theory, the child hasn't died at all, but is living in parts.
This book follows the harrowing journeys of three different children who are set to be unwound as they make their escape, through something very like the underground railroad of the past, to a place where they believe they'll be safe until they turn 18.
It's a tense, fast-paced book. The characters are likeable and believable, and I was just hooked on the story once I started.