It's rare to find truly hard science fiction written for a young adult audience, but this book is precisely that. Several centuries after humans have colonized the stars, Stephanie Harrington finds herself on a frontier planet, bored out of her incredibly intelligent mind. Though humans have lived on Sphinx for about fifty years, no one has even guessed at the existence of a native sentient species, not to mention one that loves celery! Stephanie manages to meet one named Climbs Quickly, and though they cannot communicate with each other, they share a deep empathic bond. And once the treecats are discovered, Stephanie and her family and friends must do the best they can to protect them.
There's probably a bit more explanation of scientific and political ideas than I would like, but this book does make for a very good introduction to the hard sci fi genre. Precocious teenagers will definitely identify with Stephanie, and the issues put forth in the book are ones that deserve real thought. It's the first book in a series, and while I don't know that I'll read any more of it, I would definitely recommend this to young adult readers.