The year is 1985. The Cold War is in full swing. Aldrich Ames (Paul Rhys) sits inside a DC-area restaurant. He orders a martini while thumbing through a file filled with top secret documents. He downs a series of drinks while waiting for someone who never shows. Ames heads over to the Embassy for the U.S.S.R. He mentions that he works for the CIA. He then turns over the top secret files.
CIA counter-intelligence officer Sandy Grimes (Jodie Whittaker) heads to work. Aldrich Ames is part of a staff meeting where an unnamed asset is the topic of discussion. Sandy reveals that this person inside the U.S.S.R. is a high-ranking KGB officer who gave the CIA valuable intel in the 1970s. Ames is concerned that doing a money drop for the asset inside the country is too risky. Nevertheless, the mission is a go. The case officer sent to make the drop is followed. He manages to lose the tail until another shows up later. This tail is also ditched. The case officer seems to be in the clear.
The case officer makes the money drop. Moments later, a swarm of men capture him and the rogue KGB officer who was to pick up his delivery. The case officer is beaten and interrogated by the KGB. He's branded as a spy. He's asked to confirm that the other man was his asset. Back in Washington, the CIA believes their asset may have been compromised. Sandy reveals to her colleague, Art O'Neill (Stuart Milligan), her fears about what will happen to the case officer, who is suddenly and unexpectedly released. Sandy is relieved to hear this, but realizes the asset may have been compromised. Actually, he's been shot dead.
At the case officer's debriefing in Washington, he explains all that went down in the Soviet Union. Sandy gets word that the asset has been executed. She's visibly shaken. Her family knows something is wrong, but she can't talk about what's troubling her. Sandy is brought before the Director of Central Intelligence. She learns that more assets have been lost recently than any time in history.
After a pep talk from her understanding husband, Sandy goes to work on this troubling situation. It's not long before she figures something out. She tells Art that the asset in the park during the money drop was a plant. The whole thing was a set up. They knew the real asset was a spy and had likely been captured long before the drop. That means the KGB is hiding the true problem. Sandy believes they have an in to the CIA. She tells Aldrich Ames that she hasn't solved everything yet, but will get there eventually.
Back at home, Sandy makes a nice, big breakfast for her family. It's a rarity for the entire family to share a meal together. Everyone is pleasantly surprised. At the office, Art tells the big boss about Sandy's theory. He's ordered to get to work on it. In Italy, a man claiming to be a senior counter-intelligence colonel in the KGB makes a phone call. He says he is standing outside the U.S. Embassy. He lets the person on the other end of the line know that he wishes to defect.