G, Kensi, and the office crew continue to pursue the wrongdoers and the missing nuclear bombs while Sam and Deeks remain in custody; later the team gather on a helipad, where they hold a shootout; a NEST team seizes the bombs.

An aircraft crashes in Burbank, killing all aboard. At first it appears the pilot inexplicably flew straight into the runway, but as the team investigates they find evidence of murder. Nate returns to evaluate Sam and Deeks.

Deeks returns; in LA the CEO of a biotech firm dies in an explosion of his car; the firm does research for a vaccine against the deadly ricin virus; the G team figure out the bombing and a theft by extortion, and they catch the bad guys.

Someone abducts a German immigrant man; Hetty sends G to Camp Pendleton; everyone else on the team starts working on the abduction; G tails them and joins them; Arkady lends a hand; the gang figure out some of it, and Hetty tells the rest.

In broad daylight three bad guys forcibly abduct Robin, the girlfriend of William, a recently discharged Naval intelligence officer, who specialized in the design of highly classified drone navigation; G and Sam find William in his office, and Nell joins them; a bad guy calls William, so the foursome converge on a building just in time for an explosion; Eric belatedly catches an important clue; William and Oscar, his business associate, make admissions; the foursome rush a rural shack and wipe out the kidnappers, but they do not find Robin, whom Nell then sees at William's office; G and Sam take William and Robin to the boatshed; Eric joins Nell in the field to protect his interest; on G's order Kensi and Deeks shift gears, and they produce; Nell uses a piece of hardware to detain Oscar for G and Sam, who have put the pieces together; the team take the bad actors in custody; all six of the field workers head out for a debriefing over cold beer.

A joint task force (involving the CIA, FBI, and NCIS) raid a meeting in a house in an attempt to capture members of the Molina drug cartel and the Al Qaeda; however, they walk into an ambush; the new SecNav, suspecting a mole or other leak, directs the Callen team to investigate and correct; at the boatshed Kensi and Deeks interview four participants in the raid; Eric determines that the problem is not a mole but rather a hacker, which, Hetty says, is even worse; on the cellphones of two agents Eric discovers the hacker's malware, which allowed the hacker to intercept all calls, both incoming and outgoing; in an alley the foursome grab the hacker (Cindy, a 15-year-old girl) and her laptop computer; G suddenly becomes a substitute teacher, then he finds the track coach wearing a belt as a necklace; Eric finds a link and the man responsible; the gang figure out everything; with Cindy's help the team grab the bad guy who misused Cindy and her activities.

Two trespassers kill a security guard in a rail yard in LA; Hetty expresses concern about terrorism; the team soon target the rail company; a recently fired brakeman hijacks a train; the team solve the puzzle, and Sam prevents a disaster.

At a research facility of the US Department of Energy in Los Angeles, an intruder steals electronic data and leaves, then a third thug shoots the thief and his wheelman, then a security guard intervenes, and the third bad guy shoots the guard while the wheelman escapes, leaving the thief and the guard on the pavement and taking the stolen data; the guard was a retired Marine gunnery sergeant; the data pertains to an antiterrorism nuclear-detection system. G and Sam visit the home of the wheelman, whom they find dead; G and Sam visit the injured guard; Nell does a chore for Hetty, Eric provides data, and Hetty serves as backup; the foursome respond to an alarm and find a person of interest but no bomb or other hot material; Nell sees a special person, G and Sam grab him, and Hetty chats him up at the boatshed; the foursome, with Nell's help, pull a scam on a bunch of Russkis, recover the data, then move out; Granger freaks out, but everything works out.

A lieutenant commander in Naval intelligence dies at an upscale addiction-rehab villa in Malibu, near Los Angeles; Kensi and Deeks go undercover at the spa; Eric and Nell give much help; the team solve the case and prevent a major tragedy.

A masked intruder decapitates a Pentagon consultant in Bahrain and steals a flash drive containing top-secret data; the drive turns up in Hollywood; a Gurkha works with the team; they find the answers and eventually the drive as well.

A Romanian suspected war criminal and human trafficker has lived 20 years in the LA area; he eludes the FBI; the G team help to find and seize him; a CIA guy adds facts; against orders the threesome grab him; Kensi arrives in Afghanistan.

An intruder attacks a senator's daughter, but she eludes him; the senator has led an investigation of certain activities of a unit of the Chicom Army; the G team find much action and the real reason; Hetty makes gifts to Kensi and to Deeks.

A man dies in an explosion of his car; he's an undercover agent of the US Department of the Treasury, who investigated an ancient Middle Eastern technique for anonymous transfers of funds; the team solve the puzzle and prevent a tragedy.

Two dead bodies show up in an alley; the LAPD calls the G team; the vics were former military and former employees of the private contracting firm linked to a previous story; Nell goes into the field and does well; the team solve the case.

At a consulate in LA a thug kills the envoy and two security men; he tries to lay the blame elsewhere; G and Sam go to Mexico City, take part in a rumble, and return with an old friend.

At a fish market in LA an explosion kills two employees; G, Sam, and Deeks look for evidence of international terrorism; while working with a DEA agent, the team solve the case and find the bad guys; Kensi overseas takes a shot but misses.

In LA a local gang torture and execute an ATF undercover agent, who worked with the US Navy on a joint task force; G and Sam find the body and a clue, which leads to a club, where the team solve the case, find a leak, and take care of it.

While Eric and a buddy, Ira, play an online game, a sniper opens fire on Ira's pad, and thugs break in; the G team look into security involving Russia and Chechnyan separatists; the team safely work out everything. Kensi remains in trouble.

Hetty, suspecting that Kensi has become a prisoner of Taliban insurgents, sends G, Sam, and Deeks to aid her; G, Sam, and Granger overcome trouble and find Kensi and another; Deeks produces help; all works out; the gang prepare to go home.

In LA two Iraqis demand money from a discharged Marine, who's also a former security contractor from Iraq and a recently released federal prisoner; the Callen team find surprises, explanations, and bad guys; Kensi returns to field work.

G and Sam abduct an undercover NCIS agent suspected of having turned to the side of the smuggler whom he's investigated; Kensi and Deeks play head games with the agent, G and Sam play them with the suspect, and the teams win on all counts.

At an avionics firm in LA four armed thugs steal a flash drive containing software pertaining to a drone for the US Navy; Sam knows the lead engineer on the drone project; the G team figure out everything and find the bad guys and a child.

During a Marine-sponsored charity-benefit volleyball tournament at Venice Beach, a car bomb explodes, killing two and injuring 29; promptly an aggressive TV reporter, Dana, says on the air that, according to sources, an Iran-based Islamic militant group, the JLF, is responsible for the bomb. One honcho at the DoHS firmly denies that the JLF is responsible; G and Sam lean on Dana, who gives a name; Eric finds another lead; Eric and Nell exchange notes; Kensi and Deeks chat with a man who believes in alien creatures who watch everyone; G and Sam make a productive stop at a car-rental shop; Kensi and Deeks learn some disturbing news; Dana dies, and Sam collars her killer, Bakri Deng, from South Sudan, who first refuses to cooperate; Kensi and Deeks learn about Deng, and Eric and Nell learn even more; G and Sam find the truth and an explanation, then, with Deng's help, they intervene with two other bombs and bombers and neutralize them. The foursome also receive love notes.

While investing the death of a missing submarine officer, which first resembles a suicide, the G team find conflicting clues and other evidence; G and Sam discover a distinctive vessel, they board it, and it gets underway. [Continued.]