A crucial agent crumbles under emotional distress and threatens to topple a valuable network of KGB informants. Professionally, Philip and Elizabeth are tasked with infiltrating the FBI's new communications encryption system while personally they are forced to grapple with one of the darker aspects of life as a spy.
Elizabeth meets with Adam Dorwin, a manager of a private company contracted by the U.S. government for the missile defense program. Dorwin is later revealed to be a KGB agent codenamed "Udacha", and feels nervous and alone because the KGB cannot contact him out of fear of the FBI capturing him; the FBI has new encrypted radios so the KGB cannot tell when they are being followed. Elizabeth turns her focus on another man who handles the technology, and learns the encryption devices are mobile. She and Philip track down one of the mobile units in the trunk of an FBI car. Elizabeth manages to make an imprint of an encrypted card, at the risk of being caught in the car's trunk. Meanwhile, Stan pressures Nina into learning if the KGB will meet with Udacha. When the code is learned by the KGB, the meeting is set. The FBI knew of it and follows Udacha's contact to the supposed meet, while Elizabeth kills Udacha at another site. These actions force the KGB to realize they have a mole.