As the Cold War enters its final act, the CIA is sent scrambling when a rendezvous with a prized asset goes horribly awry. CIA officer Sandy Grimes begins her investigation into the source of the problem and quickly discovers that this lost asset is just the tip of the iceberg. Little does she know that this is just the beginning of a decade-long mole hunt, and the mole is one of her cohorts - Aldrich Ames.

The CIA scores a major break when Vitaly Yurchenko, a high-ranking KGB officer, defects to the US. Assigned as the lead in the debriefing, Aldrich Ames engages in a verbal cat-and-mouse game to determine whether he is in danger of being ratted out. Ames considers taking drastic measures when Yurchenko reveals that he knows of a mole in the CIA. Meanwhile, Sandy frets over the safety of a beloved and esteemed asset, General Dmitri Polyakov.

After Yurchenko's shocking disclosure, the CIA and FBI mobilize to bring the brilliant Edward Lee Howard to justice. Despite Howard being fingered as the mole, Sandy remains concerned about potential agency leaks and works tirelessly to prove that her asset, General Polyakov, is attempting to establish contact with the CIA. With the rest of the CIA distracted by bigger matters, Ames develops an unlikely bond with Yurchenko during a trip to Canada.

After learning that a breach remains at the CIA, Sandy butts heads with Jeanne Vertefeuille, the senior officer conducting a thorough review of their operations. Jeanne's presence also rattles Ames, who feels increasing pressure from the Soviets to provide more information. On the home front, Ames feels even more pressure, caught between his love for his wife Rosario, and placating her spendthrift lifestyle.