Edessa, a Roman outpost, is on its last legs, besieged by Persian troops. Roman Emperor Licinius Valerianus agrees to meet his adversary to draw up a peace treaty, but it is a trap, and the Emperor and his 12 guards are chained and dragged away. After months of forced labor the Emperor dies, but his guards make a daring escape lead by the heroic and enigmatic chief, Marcus Metellus Aquila. They meet an exiled Chinese Prince, Dan Qing, and agree to safeguard his journey home to reconquest his throne from his mortal enemy, a eunuch named Wei. Thus begins the adventures of the Romans and the Prince as they journey to China. There they will discover that they aren't the first of their kind to arrive in China: they were preceded centuries before by the survivors of the "lost legion."