A surprising discovery leaves Alex reeling as he tries to adjust his theories in light of what he found at Philadelphia City Hall. Meanwhile, the Rezident questions Katya and Mark's dedication and Natalie discovers the dangers of Black Dagger.

The FBI think they have a mole, so an investigation gets underway, and it puts Alex at war with his own ethics. Elsewhere, Victor devises a new method for staying on top of the O'Connors and Natalie makes a grievous error while searching for a lead.

Sam and Alex join forces to find Oscar Christoph. Victor plots to take down the Rezident.