Sydney and Jack warn a disbelieving Vaughn about their suspicions of Lauren being the CIA mole. Meanwhile, Kazari Bomani and Sark take possession of the Rambaldi machine as part of their greater master plan. Sydney and Vaughn must stop a Covenant virus that's crippling medical facilities around the world. Sloane's secret of being Sydney's biological father is revealed to Jack, and Bomani begins to lose faith in Lauren's ability to carry out her Covenant missions.

Lauren stages a stunning betrayal by impersonating Sydney and blowing up the CIA offices to steal classified materials, and nearly killing Marshall in the process. But Sark is captured during Lauren's escape, and Sydney decides to play the impersonating game herself to learn where Laura is heading off too. Meanwhile, Vaughn comes face to face with his darkest demons in pursuit of his traitorous wife. Nadia must decide whether or not she can trust her father, Sloane, in the pursuit of Rambaldi's most priceless artifact and escape from CIA custody. During a mission to South Africa at a Rimbaldi artifact dig, Sydney has a some help and hindrance from Katya Derevko, as well as a final one-on-one fight with Lauren. Afterwards, Sydney receives a shattering revelation from Lauren that will make her question everything (and everyone) she thought she could trust.