Elizabeth and Phillip are supposed to get a biological weapon sample but fail to make the exchange when someone is watching. Nina works Anton in hopes it will lead to her freedom. Paige wonders if she can trust Pastor Tim with her secret.

Philip tries with increasing desperation to get rid of a sensitive and dangerous package as family tensions in the Jennings House reach a boiling point when Paige shares a secret of her own.

Paige copes with new burdens that come with her family's secret - as Philip and Elizabeth struggle to contain their cover without destroying their daughter.

A devastating flaw during a mission forces Philip, Elizabeth, William, and Gabriel to confront the depths of their patriotism... and their mortality. In Russia, in striving to be a better person, has Nina put her life on the line?

Philip must consider his life with Martha and make a crushing choice from which there is no coming back.

Martha must finally face the truth she has denied - and her life may never be the same. Plus, a chilling new development in William's work forces the Jennings to face the realities of what a biological war would mean.

The Centre rushes to prepare Martha's exfil as Directorate S agents try to locate her but, it seems that a backup transport was also ordered. FBI tears up the Clark Westerfeld apartment. Martha almost walks into the FBI dragnet. Philip is overcome with self-recrimination...KGB may kill Martha. The FBI intercepts a call to Martha's parents from Woodley Park and stake out the area. Philip gets a call from Rock Creek Park; Elizabeth races to reach her and brings her in bruised but alive. Oleg does not know why backup transport was ordered. Gaad waxes philosophical about his FBI career in flames as the Jennings kids drink beer with Stan's son. Philip is finally honest with Martha, over Elizabeth's objections. Martha knows that she will be completely alone in Moscow. Will tomorrow's plane carry one rat or two? Or will Martha bite the Valium bullet and refuse to be forced to defect and commit further treason?

The Jennings hit their breaking points as they try to handle their local agents such as Martha.

The Day After premieres, making the stakes - and terrible consequences - of the Cold War plain. Even with that in mind, will Elizabeth be able to complete the painful process of the "Patty" operation?

When Paige's long-ago indiscretion threatens to resurface and destroy the family, Philip and Elizabeth find themselves scrambling - and Paige finds herself reevaluating who her parents really are.

Elizabeth completes the last steps of a very personal operation... but at what cost?

As Paige deals with last episode's trauma, she sees her mother in a new light... and finds she has inherited some of her parents' skills. Plus, has Oleg reached his breaking point with Stan?

In the season 4 finale, Elizabeth & Philip race against the FBI to retrieve a mysterious package. Paige finally begins considering whether or not she would like to enter the family business.