returns from a game of racquetball with Stan Beeman, when Elizabeth informs him that they have a job – stopping a contract assassin who has been hired by the KGB to kill American scientists. The KGB changed their minds on the mission, but give Philip and Elizabeth no information on what he looks like or who he will kill first. Philip and Elizabeth monitor the house of one of the scientists. They plant a bomb under his hood and kill the engine in the hope that he notices the bomb, which he does, and gets his wife to safety. Philip blows up the car, forcing the U.S. government to give the scientists protection. Elizabeth meets Claudia, where Claudia informs her that Philip did in fact sleep with Irina, despite Philip telling Elizabeth that nothing had happened between them. At the FBI headquarters, Agent Gaad has instructed the agents to find out who blew up the scientist's car. He gives Stan the keys to a safe house so that he and Nina can meet in private. Elizabeth, in disguise, goes to the contract killer's only US contact. Before she can interrogate him, his young daughter draws a shotgun on Elizabeth. Philip takes the gun from the girl and they find out that the contact sold explosives to the assassin, whom he describes as a "chubby," "friendly guy". He gives them pictures he took of the assassin when he visited his house. After an awkward dinner at the Beemans', Philip asks Elizabeth why she is giving him the cold shoulder. She tells him that she knows he slept with Irina. Philip apologizes and asks for a second chance, but Elizabeth declines. Philip asks Martha, Gaad's secretary, about Gaad and the FBI's knowledge of the bombing. Martha volunteers to find out what Gaad knows and later makes copies of secret files that Gaad gave to her, but is briefly interrupted by Chris Amador, whom Martha used to briefly date and who asks her out. She declines and brings the files to Philip, citing suspicious foreign nationals that came to the US in the past week, with information on hotels in which they are staying. Philip and Elizabeth go to the assassin's hotel room, with Philip kicking the door down and pulling a gun on him and Elizabeth entering through the window and doing the same. The assassin backs himself near the bathroom and signals to a bomb placed on the wall behind Philip. The assassin draws his gun and a gunfight ensues. As the assassin is attempting to detonate the bomb, Elizabeth tosses it into the bathroom where the assassin is hiding; he accidentally blows himself up. An FBI agent shows up for his shift protecting a house accommodating one of the scientists. Before his death, the assassin had placed a bomb inside the FBI agent's walkie-talkie. Soon after, the house blows up, killing the scientist and three agents. After hearing the news on the phone, Gaad swears to his agents that those responsible will pay. Philip and Elizabeth return home. He tries to apologize to her, but she doesn't accept it. He then tells her if she doesn't want to be married to him, The Centre would have no objection. On her return home, Amador watches Martha from his car.
Production
The episode was written by Joel Fields and series creator Joe Weisberg and directed by Bill Johnson.
Reception
In its original American broadcast, "Mutually Assured Destruction" was seen by an estimated 1.65 million household viewers, according to Nielsen ratings.
