Throughout the book, Rosie grows from a headstrong, stubborn child into an intelligent and courageous young woman. With the help of a rare talent—beast-speech, a small bit of magic unknowingly passed on from Katriona—and the silent encouragement of the town's taciturn blacksmith, Narl, Rosie becomes a talented and well-known horse leech, more inclined to wear breeches and whittle spindle ends than wear dresses and practice embroidery, as her more ladylike friend Peony does. However, when Rosie is 20 years old, Ikor, a mysterious powerful fairy, appears and reveals to Rosie that she is actually the country's hidden princess, and announces a plan to defeat Pernicia: a spell will be cast over Peony and Rosie which switches their identities, but only until Rosie turns 21 and Pernicia's spell is broken.
