He was born in the Pyrenees. A close friend, called Acco, killed a bear that was sacred to the goddess, Pyrene. Her resultant enmity made it essential for him to leave his homeland as an exile, so the two friends decide to join the Roman cavalry. Camul hopes to return home after some years, but Acco knows he will never do so. Throughout their travels they feel pursued by the goddess, who appears under different names in different places.
After participating in a frightening battle against the Germans the two become friendly with an influential Roman, the son of a Consul, who takes them with him to Rome. The Consul is planning a campaign against the Parthians, with the aim of winning a lot of booty and enhancing his political standing by gaining an easy victory. After a lengthy delay the army finally sets off for the east, although as it leaves the city a Tribune pronounces a curse on it and foretells disaster.
They march through northern Greece and into Syria, where Acco has an encounter with the goddess that indicates her malevolence is still very active. Finally they march off across the desert on an ill-judged and badly-executed invasion of Parthia, which ends in disaster. Acco is killed and Camul is captured, although his life is spared because he showed loyalty to his commander, the Consul, when his other attendants fled.
Duggan gives us a lot of information about the Gauls' outlook on life and on conditions in the Roman army. The narrative moves ahead briskly except in the somewhat lengthy interlude in Rome, where not a great deal happens. The desert episode is the climax of the book and is described vividly.