The Eagle of the Ninth opens on a well-traversed road in southwestern Roman Britain, as the Fourth Gaulish Auxiliaries of the Second Roman Legion march to the fort of Isca Dumnoniorum. Leading the cohort of 600 men is Centurion Marcus Flavius Aquila, who at 19 years old has assumed his first command and will be responsible for assuming control of the fort. As he rides at the helm, Marcus reflects on the events that brought him to this point and the aspirations he is confident this career trajectory will fulfill. A decade before Marcus’s arrival on the island of Britain, the Ninth Legion, in which his father served as First Cohort, disappeared, and along with them their sacred eagle, the precious emblem entrusted to their care.

Marcus has specifically requested to serve in Britain, believing that the most promising opportunities for discovering the fate of his father’s legion will present themselves in the place from whence they vanished. Marcus has set his sights on advancing through the ranks to serve in the Egyptian Legion and intends to reclaim his family’s farmland in the Etruscan hills upon his retirement from the military. In the interim, his deep sense of paternal loss, desire to learn his father’s fate, and need to understand what became of the Ninth Legion have driven him to integrate this search into his military plans.