Mason Kane of spy organization Citadel crosses a new organization , Manticore, leading to a bad accident. Eight years later, Mason is living quietly as Kyle Conroy, with no memory of his past, until an old colleague asks for his help.

Kyle and Bernard journey to New York City to steal the Citadel X Case from Manticore Headquarters before it's too late. Later, Kyle learns that a figure from his past is still alive and he risks everything to find them.

As Kyle and Nadia land at an old safe-house, small clues about their past life together bubble to the surface. Soon, they discover a former ally who may be key to stopping Manticore is imprisoned in a facility in Morocco. In order to rescue him they first have to enlist the help of a local crime boss. But their mission is compromised as secrets of the past are unearthed.

After the shocking revelation of Abby's former identity, we learn of the past entanglements between Mason, Nadia and Celeste, and a horrific decision that reverberates still today. Meanwhile, Nadia and Kyle land at the Manticore compound in Morocco and risk their lives to free their fellow spy. But their hero's welcome is short-lived as they are forced to grapple with a dangerous accusation.

Nadia, Kyle and Carter are forced to work together to escape from Manticore and protect the X Case, but suspicion of one of our heroes reaches a boiling point, leading to an explosive reckoning.

In the epic conclusion to the season, with one of their own being held hostage by Manticore, Kyle, Nadia and Carter risk everything to save them and thwart Manticore's plans to acquire nuclear weapons.