Philip and Elizabeth are given an urgent task to plant a bug in Defense Secretary Caspar Weinberger's office; Stan closes in on a member of the Soviet Rezidentura.
A crucial agent crumbles under emotional distress and threatens to topple a valuable network of KGB informants; Philip and Elizabeth are tasked with infiltrating the FBI's new communications encryption system.
A mole hunt within the KGB causes suspicion amongst allies and shatters trust within the Jennings' marriage; Stan's plan to keep his mole safe puts her at even greater risk of discovery.
Philip and Elizabeth must stop an assassin from taking out key U.S. scientists; Grannie shocks Elizabeth with the truth of what happened between Philip and Irina in New York.
McNulty gives up on identifying his Jane Doe; Sobotka tries to play a political game on behalf of his union; D'Angelo wants to live outside of Barksdale's umbrella.