A young CIA analyst learns that his family is part of a Russian sleeper cell in this modern-day spy drama.

Mark and Katya are nearly exposed as spies by their own son, Alex. Then, in a brilliant bit of manipulation, Katya manages to convince Alex he is wrong. Katya's lies cause a rift between her and her husband and son. Victor is acutely warned of what will happen to him if he doesn't keep the O'Connors on a tight leash. Meanwhile, Alex partners with Agent Michelle Prado as part of a joint CIA-FBI task force to find the hidden SVR cache before it's destroyed. Alex's unique perspective is the key to unmasking the identity of a new defector, leading to a deadly confrontation with an SVR hit team.

In the aftermath of a violent shootout, Alex must convince the FBI to risk a dangerous covert operation to find Mikhail's hidden cache. With Agent Prado at his side, Alex leads a team to Philadelphia to retrieve the laptop from a secure government building, but Victor is a step ahead and orders the O'Connors to break in and steal the laptop first. Meanwhile, Katya discovers one of Natalie's most dangerous secrets, and forces her to choose between love and family.

A shocking discovery leaves Alex struggling to reconcile his theories with the evidence found at City Hall, and Sam encourages him to keep looking for clues. Meanwhile, Mark and Katya must answer for their actions when the Rezident doubts their commitment to the cause, and Natalie learns just how lethal Black Dagger will be if they don't stop it.

Alex is confronted with the reality of his family's past just as his integrity is questioned at work. The FBI suspects a mole in the organization and brings in Special Agent Faber to investigate. Faced with testifying under oath and submitting to a polygraph test, Alex must for the first time fight against his own moral standards. Meanwhile, Victor finds a new way to keep tabs on the O'Connors, and Natalie makes a critical mistake while tracking down a lead.

Natalie must rely on an outsider for help finding important information on Black Dagger.

Alex (Gavin Stenhouse) goes to Rome, Italy with a dangerous double mission -- slip away from the CIA/FBI task force to track and identify the contractor handling multi-million dollar payments for Black Dagger. Katya (Hope Davis) asks a friend to help her son in the field, and Alex is surprised to learn details of his mother's heroic past. Sam's (Kenneth Choi) attempt to buy a cache of SVR intel from a dangerous Italian broker is stalled when his cover is blown. Meanwhile, Victor (Morgan Spector) shows Natalie (Margarita Levieva) his contingency plan, and Alex's professional relationship with Michelle (Floriana Lima) gets very personal.

Alex brings important intel back from Rome, but Mark and Katya need Victor to fill in the missing pieces by spying on the Rezident. Sam seeks advice from Faber after he catches his protégé in a lie, and Michelle reveals to Alex the intimate details of her past. Meanwhile, Christoph makes the final preparations for Black Dagger before arriving in America.

Alex (Gavin Stenhouse) puts Michelle (Floriana Lima) in grave danger by telling her the truth about Black Dagger, while Sam (Kenneth Choi) and Faber (Paul Ben-Victor) try to track Alex when he goes off the grid. Victor (Morgan Spector) takes drastic measures to keep Natalie (Margarita Levieva) safe from harm, and Christoph (Giancarlo Esposito) arrives in New York undetected, to carry out a test run of Black Dagger. Meanwhile, Mark (Scott Cohen) witnesses the toll his choices have taken on his children's lives.

The task force makes a move against Alex, setting off a string of events that finally reveal the mole's identity. Mark and Katya uncover the name of the operative behind Black Dagger. Victor and Natalie try to adjust to new circumstances.

Mark and Katya confront the mole, but an escape puts Sarah in grave danger. Now branded a traitor by the task force, Alex goes on the run but tries one last time to reason with Sam. Meanwhile, Christoph targets a woman who can help him carry out the Rezident's plans, but faces some unexpected complications.

Victor (Morgan Spector) devises a plan to infiltrate the SVR and cut the head off the snake. Alex (Gavin Stenhouse) convinces Katya (Hope Davis) to send Sarah (Alex Peters) somewhere safe. New information brings Sam (Kenneth Choi) one step closer to finding Christoph (Giancarlo Esposito), whose mission is suddenly complicated when Elizabeth (Diane Farr) confesses a secret.

In the explosive season finale, Alex (Gavin Stenhouse) comes face-to-face with Christoph (Giancarlo Esposito) and learns the deadly magnitude of Black Dagger. Mark (Scott Cohen) and Katya (Hope Davis) devise a plan to stop the operation, but realize it may cost them their lives. The Rezident (David Vadim) gains an advantage over Victor (Morgan Spector), but Natalie's (Margarita Levieva) actions may turn the tides for good.