"Rosie the Horstorian" centers around seven horses and two cats living in the same barn. Among the horses, Rosie is a P.O.A (Pony of the Americas) mare that has extensive knowledge of horses living in the past, making her a horse historian, or horstorian. She tells stories about the very first horses - the "Dawn Horses" - and their adventures in the Eocene era. She tells another story concerning the deep friendship that develops between a young, Bedouin girl and her family's prized Arabian filly. Ample scientific and geographical research on the author's part lends a level of realism to the stories, immersing the reader even further into Rosie's tales. Interspersed among these two tales are the horses, cats, and their responses to the stories.