The Last Hunt — Bruce Coville

In the center if Luster stands an enormous tree called the Axis Mundi, the Heart of the World. But now that tree is wounded, pierced through by magic. And through that wound marches an army of Hunters, led by the sinister and vengeful Beloved. And they are all determined to destroy each and every unicorn.

As the unicorns gather to defend their lives, the human girl, Cara, is sent on a mission to meet a ferocious and mysterious dragon. Faced with perilous danger, Cara must make a desperate decision that will change her life forever.