In a beach town on the Black Sea in Romania, G, Sam, Kensi, and Deeks check out the neighborhood while Hetty chats with the head of the Comescu family, who describes a connection to G. The team shoot their way into a house and save Hetty.

In Beverly Hills two masked thugs kidnap a wealthy and successful software developer; Callen and company help the National Security Agency; the team find the pieces and put them together, then they find the missing guy and the bad ones.

A Marine staff sergeant dies in an explosion of an SUV; Callen and company investigate; Hunter makes changes; Sam and Deeks find a runner and a bomb; the team find the bad guy; three more bombs explode, but the gang escape; Hetty returns.

On the oceanfront at Venice, California, in the Los Angeles area, an unknown gunman kills a TV journalist, Adriana Gomez, who has received death threats from Libyan nationalists (after she created a series of stories about an anti-Qaddafi rebel and folk hero); Gomez contacted a commander, Gavin Madison, in Naval intelligence, who's an expert on Libya; Callen and company investigate. G and Sam visit Cdr. Madison at home, find two bad guys, exchange fire, and drop one and lose one; Kensi and Deeks visit a Libyan restaurant and get a lead; G and Sam check out a defunct auto-glass shop, where they find a large clue; Kensi and Deeks, along with G and Sam, rediscover the loose Libyan; G and Sam find also a body in a trunk; Sam goes shopping for a lamb, and G, Kensi, and Deeks pitch in; they meet people and deal with them. The team figure out the puzzle and create a solution, which includes Sam's making announcements. Hetty tells G more about his ancestors.

While raiding a pawnshop, targeting a Mexican drug cartel, LAPD cops kill two cartel grunts plus a wanted Muslim terrorist; the LAPD requests help from Callen and company, who seek, find, and scrub an alliance between the two rogue groups.

A woman former lieutenant commander in Naval intelligence dies by gunfire; Callen and company find confusing and conflicting clues, but they put all the pieces together; Hetty again visits an old friend but says that she arrived too late.

A separated Marine attacks and beats a Japanese man tourist, who dies later; Callen and company investigate; the Marine tells a long story, which eventually becomes confirmed; the team, using extreme tact and discretion, achieve their goal.

The team are sent to the Mexican desert when a Naval Seaman is murdered over a mysterious box.

The CIA loses contact with Sam in Sudan with a CIA task force; two CIA agents die, as does a third one; G goes to Khartoum and lends a hand; the gang in LA help, and they find and deal with a mole; G and Sam return to LA and take a friend.

During a sting Deeks appears to blow away an unarmed bad guy; Hetty fires Deeks after the LAPD cuts its ties with the NCIS; Kensi belatedly learns about a ruse; the team and the LAPD together find a mole, the bad guys, and some explosives.

At a college a man steals an experimental electromagnetic-pulse weapon, which has the capability to render disastrous damage; Callen and company investigate the theft and a second one, and they figure out the case and provide a resolution.

G decks a man, who is the new assistant director, and who briefs the next case. A man dies of a gunshot, said to be self-inflicted, by his wife's firearm; both have worked for a think tank under contract to the DoD; the team solve the case.

Both Alex and Jada, from Sudan in a previous episode, have reappeared in Los Angeles; while two NCIS agents (on a protective detail) escort Jada to an office in preparation for her giving a deposition, a masked man in an SUV attacks the trio in their car and escapes without injuring anyone. Kensi and Deeks get a name from Jada, then check a warehouse and catch a bad guy; Alex and his family disappear; Sam offers to play water games; Nell finds Alex, then the foursome chat with him; his behavior perplexes everyone; Kensi and Deeks visit an international business firm, from which they acquire important data; Alex finds the gang, surprises them, and chats them up, then they all pitch in and change their plans. Alex calls the main middleman and proposes a deal, which blows up; Alex gets his family back, and the gang keep Jada but lose the middleman, although another agency catches him later.

G and Sam acknowledge the fifth anniversary of their service as partners. Just outside the LAX airport four masked armed men stop a bulletproof van of the Diplomatic Security Service of the US Department of State, moving two couriers and a wooden crate, having originated in India and now bound for a warehouse in downtown Los Angeles; the bad guys seize the crate and escape with it; Callen and company investigate. G and Sam interview the couriers; Eric and Nell trace one of the trucks, two of the bad guys, and a van; then Kensi and Deeks find the van and the crate, check out the contents, and take part in a gunfight; a crew takes possession of the crate. Granger, the new assistant director, shows up and shows interest; Kensi and Deeks find a body and shoot a fed to death; G and Sam meet a private aircraft and suddenly meet also more people than expected; Sam attacks G, but Kensi and Deeks ride to the rescue; back at the boathouse the team put it all together.

Two men die in LA; a visitor, introduced as an Interpol agent, seeks help with a link to a closed NCIS case; Callen and company pursue a chameleon, who promises to kill G soon and tells why; Granger says he's there to catch a killer.

Granger summons Kensi to the boathouse; Hetty summons the others to the ops center; Kensi's father's fellow Marines have started dying, and Granger wonders whether Kensi is involved; the team start investigating and producing. [Continued.]

Kensi took a round to the torso but, wearing a bulletproof vest, survived; she steals away, hunting the shooter; she clobbers a tail and borrows his wheels; the team put the pieces together and catch the bad guy; Kensi visits her mother.

In LA a man survives gunfire while trying to enter the Vietnamese consulate; G and company investigate; the victim's personal effects include the name of a Marine first lieutenant; the team save lives, solve the case, and reunite a family.

A group of Marines find the dismembered body of a Navy ensign; Callen and company investigate; circumstantial evidence points to a SEAL, but Sam refuses to believe; Sam, a SEAL, hears the whole story; Callen learns the cause of death.

A bomb explodes in the bed of the pickup truck of a Marine former second lieutenant; he runs; FBI agents bust him; Granger wants to find out why the team did not previously know about a terrorist plot in the LA area; they figure it out.

G and Sam return from an investigation in Honolulu; Danny and Chin, of Hawaii Five-0, accompany them; they seek to intercept a rogue epidemiologist with smallpox virus; the team figure out the case and prevent an unimaginable disaster.

Kensi and Deeks go undercover as a married couple housesitting in a gated community to identify a Russian sleeper agent believed to live in the neighborhood; a Russian businessman, who's also a link to the unknown agent, dies at a local hotel. G and Sam visit an old Russian friend of G, and Kensi tries to visit an aged neighbor; they all get reactions; Eric finds a lie, so Kensi sniffs around and finds herself in a chick fight; the other girl agrees to tell all, but she too dies; still, though, she gives a Russian name, and she says that he is nearby. G and Sam return to Arkady to find out why he lied; they find the dead body of Arkady's bodyguard plus two men trying to kill Arkady; Kensi and Deeks go to an interesting dinner, and Sam shows G a disturbing image; on the way home Kensi and Deeks run into trouble with a gay couple; however, they discover the Russian long-time sleeper agent, who recently became active. The team finish putting the pieces together.

A driver causes a wreck and shoots to death the second driver; a third one blows away the first; SA Renko of the NCIS is an undercover worker of the gun shop where the first two men worked; the team find the bad guy behind it. [Continued.]

The Chameleon says that he'll walk; he tells about Renko and the Mayfield family; he demands an exchange of himself for an abducted NSA analyst; Granger cuts him loose, and the team escort him to the swap, but G takes action. [Continued.]