Three space miners, Calum, Gil, and Rafik, find a small escape pod floating in space. Inside, the find a baby girl with strangely shaped hands and feet and a small bump on her forehead. She grows into a young woman within a few years, with the small bump on her forehead becoming a horn. Calum, Gil, and Rafik spend several years out in space, and protect Acorna from others who see her as deformed, or a rarity to be put on display.
With a vast cast of characters (that continues to grow as the series goes on) McCaffery has created a large and interesting universe. As Acorna attempts to both adapt to various planets after spending much of her life in space, she has to hide her alien features from the general public. However, she is naive, and often gets into trouble as she tries to integrate into cultures she obviously does not understand.
This purpose of this book (and to a lesser extent, its sequal, Acorna's Quest) seems to be mainly to set up the rest of the series. It introduces us to Acorna and the various powers of her horn, as well as the universe in which they live, leaving her free to explore the cultures of individual planets in later books.
An over-all good book, if only so that you can read the other (much better) 6 books in the series.