Masinissa: Ally of Rome resumes the story of the Numidian Prince at a moment when he is beginning to question his alliance with the Carthaginian Empire during the Second Punic War. He has been fighting as a cavalry commander on the Iberian Peninsula for several years, but the fortunes of war and his own clandestine meeting with the Roman consul Scipio Africanus, ostensibly his sworn enemy, has led him to reconsider his loyalties. His love for the Carthaginian aristocrat Sophonisba, which had blossomed during his period of exile in Carthage, has remained strong during his absence from North Africa. He is due a period of leave in that city shortly to formalize his engagement to her.

At this moment in the war, the Carthaginian forces are attempting to reform their military strength in North Africa and in the strategically important and historically allied southern Iberian city of Gades (present day Cadiz.) For his part, Masinissa has recently retrieved one of the sacred cups of Melqart (Hercules) which had been hidden in a fortress now occupied by the Roman legions. He is presently taking a small contingent of his most loyal troops to the temple dedicated to Melqart, which is located close to the city of Gades, to return the cup to its proper religious location. The mood of both he and his men on the journey is mutinous.