This YA dystopian novel is the story of Callie, a teenage girl in a society where everyone except the children and elderly have been wiped out by a plague. With all of the power and money, the rich elderly ("Enders") have developed a way to rent out the bodies of the teenagers ("Starters") in order to entertain themselves and enjoy sports and other activities which their older, frailer bodies wouldn't allow. When Callie rents out her body, something goes wrong and she discovers she sometimes has control of her body, and sometimes her renter does -- and as she learns more about what her renter has in mind for her body, she realizes what danger she is in.The premise of this book was intriguing, although I am highly skeptical of everyone between about twenty and seventy being wiped out all in one blow like that. The explanation was that the young and elderly got a vaccine, but I guess the author didn't take into account the fact that working-class health professionals probably would also have had to get it? The idea of being able to disguise oneself in another's body is frightening and makes for good novel material, and I enjoyed the first half of the book where this was being played out. About halfway through, though, the plot changes into somewhat of a government conspiracy/prison break/rebel tough girl action movie, and my interest started to wane. The resolution is still kind of unclear to me, and I'm not sure if it wasn't explained well, or if I was just speedreading so much at that point that I missed it. Still, I could have appreciated the book a lot more if in the last chapter the author hadn't changed the game and led the reader to doubt absolutely everything that had happened. There's a plot twist that -- although somewhat expected -- completely changes the reader's feelings about a rather likable character, which would have been okay if I didn't suspect that Callie was falling for the same trick again in the last few pages. With the sudden revelations and twists at the end, the reader is left without any sort of closure, wondering what really happened, who is really good or evil, and how she's going to get out of this situation now, which seems even more dangerous than the original plot. So, basically a setup for a sequel, which left me feeling really unsatisfied with the ending, that -- in reality -- is no ending at all.