Keri Russell on "The Americans"

KGB spy Elizabeth Jennings (Keri Russell) worries about the safety of her children on "The Americans." (Craig Blankenhorn / FX / March 5, 2014)

The brutal slaying of a KGB spy couple and their teenage daughter sends a shockwave through the Soviet espionage network and alarms the public in Episode 2 (“Cardinal”) of “The Americans,” the Cold War drama on FX.

Investigators have yet to discover the true identities of the dead parents, Emmett (Jeremy Davidson) and Leanne (Natalie Gold). For now they’re regarded as typical Virginia residents tragically gunned down in their hotel room.

Russian spies Elizabeth (Keri Russell) and Philip Jennings (Matthew Rhys) know all about the shadow lives of their fallen comrades, of course. But they don’t know who killed them or why.

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To find out, Philip tails Fred Timbrook (John Carroll Lynch), who sold military secrets to Emmett and Leanne. Fred may have accidentally or intentionally compromised the KGB agents.

Posing as a telephone repairman, Philip breaks into Fred’s home and discovers a metal box hidden under the floorboards. But the box is booby-trapped, unfortunately for Philip, and he’s knocked unconscious by a powerful zap of electricity.

When Philip comes to, his hands are bound and he’s about to be shot by Fred. Philip stays alive thanks to some quick talking, while Fred breaks down in tears under the weight of his traitorous actions.

And that valuable data Fred passed to the Soviets? They’re specs for a state-of-the-art propeller being developed for the U.S. Navy.

At the Jennings home in suburban Washington, Elizabeth grows increasingly concerned about the safety of her kids: 14-year-old Paige (Holly Taylor) and 11-year-old Henry (Keidrich Sellati).

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Are those utility workers parked in a van across the street, Elizabeth anxiously wonders, or are they assassins waiting to make a move on her family?

“All those years, I never worried about Paige and Henry being safe,” Elizabeth confesses to Philip. “How are we going to live like this?”

“We’ll get used to it,” Philip replies stoically, “like we got used to everything else.”

Also rattled by the killings is FBI “mole” Martha Hanson (Alison Wright), who married Philip in his alter ego as Clark. After watching TV news reports, Martha fears the triple homicide was cult-related. Now she wants to buy a gun.

Philip/Clark, however, wants Martha to calm down and stay put in FBI counterintelligence so she can continue reporting on the actions of Special Agent Frank Gaad (Richard Thomas) and his relentless G-men.

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Deeply shaken by the murder of his spies is Soviet Embassy leader Arkady Ivanovich (Lev Gorn). He’s even afraid to be in the same room with an American who suddenly walks into the embassy and urgently requests a meeting.

Speaking over an intercom, Arkady nervously asks the stranger: “Who are you? What can you do for us?”

Just like the KGB, the FBI wants to determine the identity of that mysterious walk-in. The feds are quickly on the hunt after analyzing surveillance footage recorded outside the embassy.

Inside the embassy, KGB double agent Nina Sergeevna (Annet Mahendru) resists the flirtations of newcomer Oleg Nicholiavic (Costa Ronin), who’s tasked with acquiring American science and technology secrets.

Nina icily questions Oleg’s dedication to the mission, given his admiration for popular music and other aspects of Western culture.

“I’m a feminist, Nina,” Oleg jokingly responds in his defense. “I work only for Mother Russia.”

When she’s not being distracted by Oleg, Nina types graphic reports for her boss Arkady about how she’s seducing FBI Agent Stan Beeman (Noah Emmerich) and subtly pumping him for information.

Are there internal squabbles in the FBI counterterrorism division? Arkady orders Nina to find out.

And is Stan falling in love with delicate-appearing Nina? Bet your bottom ruble!