This is Book One in the Immortals quartet. Veralidaine Sarrasri, or Daine, is about thirteen years old when she meets Onua and earns a job helping with the horses. Daine has some very powerful gifts that she hasn't made peace with at this point. She doesn't really understand what she can do and what the limits are to her magical powers. She accompanies Onua on a journey, and along the way, she finds she can reach down into herself to summon creatures and to communicate with animals. Then, from beyond our world come the immortals who are intent on destruction. Daine joins the forces of good to defend our world. This is a powerful, wonderful series from the one and only Tamora Pierce.