When a US senator is brutally murdered, the crime bears the hallmark of the infamous Soviet assassin known as 'Cassius.' Retired CIA agent Paul Shepherson, who believed his arch-nemesis was dead, is reluctantly drawn back into the fray by his former boss, Tom Highland. Teaming up with eager rookie FBI agent Ben Geary, a devoted scholar of Shepherson's long hunt for Cassius, they must navigate a web of deception. Geary is convinced that Cassius has returned, forcing Shepherson to confront his past and the reality of an old ghost haunting him once again.