Li and her friends are about to enter Assessment which is where they will be tested and placed for positions across the galaxy for their mandatory 7-year conscription period. Her father is demanding and she has to spend a lot of her time in practice and study. It isn't only that she wants to succeed that drives her on however, her life depends upon it.
After an assessment period of its own, Earth was invaded shortly after Li was born and the human race exterminated. Her father, a diplomat, saved Li and raised her as an Abdolorean. If her secret is discovered her father and her younger sister will both be killed for sheltering a race designated unfit for survival. The Abdoloreans are stronger and faster learners than humans and can breathe underwater through gills. The book claims that they have a different psychology than humanity as well, but I didn't catch that.
The Last Girl on Earth is engaging and a quick read, but other than a few thin attempts in the beginning to shade in differences there was no time spent on defining what an Abdolorean is. Some discussion is made about other races on other planets, but nothing about their physiology or psychology is described other than their being meat-eaters. Li grew up in this environment, with no other humans, so she probably wouldn't know what the differences between humans and Abdolreans are, that's fair, but neither does she behave differently than a human teenager. Her Abdolorean peers and teachers, also her father, behave just like humans.
I just can't help but feel cheated. I was expecting the story of a girl raised in an alien culture with those who "don't feel with human hearts." Uh, how so? What is different about this culture other than some technology? Humanity has proven on numerous occasions it can act as heartlessly as the Abdoloreans when it set out to exterminate a race of people for being 'unfit'. This could easily have been a society of humans after a revolution and Li only a rebellious teenager. Strip away the alien nonsense and we have a solid story about a girl's determination and the tough decisions she has to make to protect herself and those she loves. The last 'act' of the book could have used a little more subtlety in my opinion, but it got the story where it needed to go.
This is the second genre teen romance I've had a problem with lately. I had a rough experience with The Gentleman's Guide to Vice and Virtue, but Last Girl on Earth's structure at least holds up better under scrutiny, and had better pacing. I like a romantic plot, but I expect a little more than window dressing if you get into sf/fantasy/historical/whatever fiction.