Deeks disappears while on an undercover assignment for the LAPD; Hetty offers help, so Callen and company lend a hand; Eric follows a trace to a Serbian bad guy; Deeks shows up and solves the case, and the team get him out of a tight spot.

In Cyprus an NCIS agent dies by murder; the killer lands at LAX, and G grabs and questions him and obtains information through a deal; G infiltrates the hit squad for the next lethal action; the team solve the puzzle and nab the bad guys.

On state-owned property near Imperial Beach, California, south of San Diego, while four Marines patrol the area (along the US-Mexico border) to support federal customs and immigration agents, unknown people for unknown reasons ambush the Marines and their Humvee; one escapes, and three remain missing; officials wonder whether the intruders are Mexican smugglers; Callen and company investigate. A search party finds the body of one Marine; the lone survivor says that one of the missing is a pregnant lance corporal, and the dead one was the father; a snitch gives a tip to G and Sam, the latter of whom checks it out while playing it cool; Nate suggests an alternate possibility; while Kensi and Deeks take a bike ride, they find something but run into trouble; G and Sam get a lift and lend a hand, then they find evidence confirming Nate's idea. G and Sam put it all together, so they confront the bad guy in charge. Nate prepares for a journey.

In a parking garage on Rodeo Drive in Beverly Hills, California, near Los Angeles, two shoppers find the body of a man less a crudely severed hand, which is missing; the victim was a Marine corporal, stationed at Camp Pendleton and assigned as a clerk in the G2 (intelligence) office with a top-secret clearance; Vance has expressed interest, so Callen and company investigate. Nell, an enthusiastic new analyst who finishes the sentences of others, has arrived for duty. Eric and Nell see a clue about the amputation; the musketeers conduct interviews; Eric and Nell find more clues; G and Sam find a body and another severed hand; Kensi, Eric, and Nell follow a trace to a Muslim jeweler in Beverly Hills; G and Sam start toward a lunch but bump into the jeweler and some friends; Kensi and Deeks meet the jeweler's wife and find a bloody knife; Sam adds a factoid; the team seek and find the real killer and the rest of the story. Kensi arranges to make a special delivery.

The 14-year-old daughter of a Navy commander is kidnapped and buried alive. The FBI and the team investigate an incarcerated serial killer with an identical MO. Sam's past helps him empathise.

In downtown LA a lone armed woman seizes a Navy recruiting station; G recognizes her as his former partner while undercover for the CIA; she asks for his help and gets it; the team find the bad guy responsible plus the rest of the story.

Two men, a Marine reservist and a plastic surgeon, die by gunfire, and a woman disappears; Callen and company investigate; Eric and Nell provide clues, and the team go to a party, where they grab the bad guys and prevent any damage.

A sergeant first-class retires from the Army, the day he becomes a civilian he is kidnapped. When his tortured body is found, the team must determine the reason behind the extreme cause of death.

In Hollywood two men ambush a limousine and shoot the occupants to death; Hetty says that the target, Renner, was a Swiss antiques dealer and black marketeer; she persuades the LAPD to allow her to take over the investigation because of the nature of a little black book, which she believes is the object of the activity. While Hetty visits a man in an assisted-living place, G and Sam visit Renner's pad, which someone has tossed; Eric identifies a man, Lee, who appears in a number of photographs around Renner's house; G and Callen visit Lee's office and break up a meeting; Eric says that Lee's two visitors are German "agricultural attachés" (that is, spies); G and Sam question a retired operative, and Kensi and Deeks also search Renner's pad, where they meet two foreigners with alternate identities; Hetty visits the Hollywood Bowl, and the four musketeers rescue her. Hetty again calls on her elderly friend, whom she finds dead, executed by gunfire. [To be continued.]

Intrigue and violence continue while several parties search for the "little black bloody book". The team investigates Cole's shooting and find a link to the murder of a cop during a traffic stop.

The team must piece together events when a recently discharged Navy lieutenant, and intelligence officer, with PTSD witnesses a shooting.

While Rose does an autopsy, two intruders blow away her assistant and steal the corpse and a van; she calls the Callen team, who investigate because of an apparent Navy connection. The team slowly figure out the puzzle.

The Pentagon discovers a breach after an online transfer of a file containing highly classified information. The team races against time and other interested parties to find the leak and retrieve the file.

Inmates initiate Moe by beating him inside a federal prison; Sam goes to him and undercover; Kensi and Deeks find a device and a plan; Hetty says there's more; an escape takes place, Sam loses someone, and a larger plan moves on. [Cont'd.]

Inside his pad by night G grabs a prowler, who works for Arkady, who gives G a tip; Kensi and her buds run a scam on a foreign businessman; G gets into a firestorm, but the rest of the gang show up and lend a hand.

Callen and Sam go undercover as motorcycle cops to investigate corruption within the force. When their contact is murdered they take on a job in hopes of catching his killer.

While Deeks follows his morning routine, during what appears to be a holdup of a convenience store, a gunman shoots him twice in the chest with a pistol; Deeks goes into surgery; G and Sam investigate at the scene; Kensi waits at the hospital; Eric and Nell prompt their computer. The team realize that two bad guys had staged the supposed robbery as a deliberate ambush; Eric traces the suspects' car to the hospital, where G and Sam see it and engage them; the driver dies, and the other man escapes but winds up at the boat shed. The team set up G for an undercover meet; while talking with Kensi, Deeks suggests a dangerous idea; Kensi tells Eric that G's walking into a trap; Kensi dashes off to the trap, and Deeks suddenly figures out who's the real target; G and Sam tear back to the hospital, but they arrive late, for the party has already ended. The team put all the pieces together. Hetty brings Deeks up to date on his next of kin.

One of Sam's aliases receives an invitation to Yemen to meet Abdul; Hetty hopes that Abdul will lead them to Saadat, Abdul's brother, believed to be a leader of terrorists; G and Nate provide backup; the team support, and it all works out.

A Latino day laborer dies, and a lieutenant commander in Naval intelligence disappears; Callen and company investigate; G and Sam find evidence suggesting an assassination plot against a visiting Venezuelan politician; the team thwart it.

When a secure facility on a military base is compromised, Kensi goes undercover to find out what the world-class thief was intending to steal.

A major player in the private-sector aerospace industry dies inside a test chamber at his facility; Callen and company investigate; Eric goes undercover as an FAA inspector; a big bang occurs; the team grab the bad guys at a flea market.

After a key witness, Ray, testifies in a federal arms-trading prosecution, he retires as an informant; the team give him a new identity, Charlie, and direct him to a new location; next Callen and company turn their attention to the missing military weapons; however, within two hours Charlie disappears after a shooting in Los Angeles; Deeks goes back undercover while the other members check out the scene. Kensi and Deeks chase around with Ray; a firefight breaks out, and Kensi takes out one shooter, but Ray disappears again; G and Sam seek entertainment and find some, then the gang take Ray's estranged wife to the boathouse, where she talks, where she and Deeks reminisce and catch up with each other, and where Deeks eventually makes a confession; G and Sam make Ray a special deal involving his pregnant honey. During another firestorm the musketeers run a scam on the executioners and therefore on the new convict in a federal prison.

An unidentified man dies after a beating and a burning; a specific radiopharmaceutical in the body implies a connection to a previous case; Callen and company grab the bad guy. Hetty resigns, disappears, and reappears in Prague. [Continued.]

Hetty turns up in Prague and proffers a message. G and Sam investigate; Eric and Nell help. G, Sam, Kensi, and Deeks go to Prague, find a lead, and follow it to Romania, where G has a flashback, and Hetty delivers the message. [Continued.]