Emperor Claudius is in danger. His personal guard, the Praetorian Guard, has been infiltrated by traitors. Summoned to Rome by Narcissus, Macro and Cato are furnished with new identities and placed, undercover, in the Guard. With each test of their loyalty they are given greater access to the conspirators' plot but are faced with the danger of detection and a race against time to save the Emperor. As they move ever closer to the mastermind, they realise that all is not as it seems...