NCIS: Los Angeles season 6

After events in "Deep Trouble" Hetty returns to OSP. Granger interrogates Charles Anderson for his submarine's capabilities; Eric assesses its route. Callen and Hanna disconnect batteries to slow the submarine. Jihadist captain Jabril cuts air and power to their forward hold. At Wilson's house, baited about Marty, Kensi headbuts Talia, who hits back; another agent intervenes. Kensi finds fertilizer receipts, realizing the submarine is a giant bomb. Deducing their San Diego target, the USS Van Buren aircraft carrier, Callen and Hanna cause a hull breach. Deeks cons Michael Wilson who names Jabril and Richard Miller, aka Worm, who cuts drugs. Eric informs Hetty, the Navy sent a P8A Poseidon to destroy the submarine. With Talia's DEA Agents, Marty and Kensi con Madge at her Chinese restaurant to arrest Worm, then convince Granger to board a helicopter. With water nosing the submarine downward, Jabril is forced to open the forward hatch. The flood allows Hanna and Callen to pull Ali Hanna and Yusef underwater, before Sam kills Jabril. The Poseidon locates the submarine and drops a torpedo. Callen and Hanna flood the submarine to make a free ascent. The torpedo hits, and they surface to be rescued via helicopter.

The team discovers one of them has been compromised during a murder investigation. Hetty is under investigation, and the DOJ investigates the team.

One of Hetty's houses is attacked, resulting in the death of her bodyguard. As the DOJ investigation continues, the team is forced to balance eluding their questions with finding who was responsible. Ultimately, Vance reveals to Hetty that the investigation into OSP was a ploy to get Hetty out of Los Angeles, protecting her from a leak inside of the agency and a subsequent attempt on her life, leading the team to discover that Mattias Draeger, an old enemy (from "Absolution"), was responsible for the attempt, and the episode ends with Callen threatening to make good on the promise they made to him before vowing that they will hunt down Mattias and kill him.

The team finds itself in danger as the mole remains inside of the agency. Nate returns to help Nell deal with the aftermath of her first kill while the OSP center itself turns into a battleground when Mattias arrives to abduct Hetty to take her to Moscow to trade her extensive knowledge for money.

DoD West Coast office was attacked with two dead and one missing survivor. Callen and Sam go to Mexico to find the missing DoD employee.

Sam is arrested for murdering a woman, and the rest of the team try to prove his innocence despite being stone-walled by the FBI and a U.S. Attorney. It turns out a former Marine student of Sam's was running a large scale identity theft operation, and he framed Sam in the murder of his accountant.

When a Greek terrorist is killed using a drone in Los Angeles, the OSP is asked to investigate. It turns out an anarchist group had hired him to build a drone missile and then killed him using the prototype.

An AWOL Marine/CIA agent is found dead, and the team goes to investigate his death, leading them to a high-profile drug lord about to be extradited to the U.S. and a major secret the deceased was holding about one of the lead attorneys on the case.

When Granger is put in the hospital, OSP is on lockdown as everybody becomes a suspect of being the leak.

When a paparazzo is killed outside the house of a high-ranking CIA officer and a Marine colonel, the team discovers the attack is one in a string of attacks on parents with children in military school. Meanwhile, the case has Sam to start thinking about his own father.

When Callen's girlfriend Joelle Taylor becomes a hostage following a security company's robbery, the team's search for the robbers leads Joelle to find out his true occupation. The team discusses Christmas plans and Kensi and Deeks finally become a couple.

Terrorists take hostages at an office building where Callen is undercover to investigate an arms dealer. Callen's team tries to extract him, only to find the building is wired with explosives.

After an attack on the U.S. Consulate in Tunisia, Callen and Sam go to the crime scene to investigate the death of two officers (one of which was a close friend of Sam's) and soon discover that Ambassador Nancy Kelly was not the intended target of the attackers, who have now entered the United States.

When the victim of a car crash is discovered to have a lethal strain of anthrax, Callen and Sam are sent to Mexico to locate the virus's origin while Kensi and Deeks try to stop the anthrax from being utilized in an attack.

When a tip regarding a missing NSA analyst results in Callen and Sam being abducted, Kensi and Deeks investigate whether their kidnapping was related to Granger's impending meeting with an ISIS informant.

When on a mission to bring in an Indian defector, Sam is shot by a sniper, leading the team to work with Jemadar Thapa (from "The Frozen Lake") to find the culprit, leading to a face-off with a team of rogue Gurkha agents and questions about the defector's true agenda. Meanwhile, Kensi and Deeks have an argument.

When an Afghan soldier brought to America for DEA training is murdered, the OSP team finds themselves tracking down his two comrades who have been targeted for the information they know about the Afghan military.

After a successful sting operation, three FBI agents are killed in a sudden explosion, resulting in OSP being assigned to investigate. Upon investigating, they learn that the agents were killed by a hidden bomb and that the attack isn't the only one - leaving the team racing against the clock to identify where the second attack is being held. Meanwhile, for the investigation, Hetty pairs Kensi with Sam and Callen with Deeks, but for a reason neither Kensi nor Deeks can guess.

After a Navy test missile is hijacked and used to destroy a civilian boat, the team is tasked with ensuring other Navy weapon systems haven't been compromised, and the team's investigation leads them to an internal conflict inside of a hackers' organization. Meanwhile, when a college graduate agent comes down to OSP to assist, Eric begins to hit it off with her, making Nell jealous.

Callen is returned to his undercover assignment in prison (as seen in "Inelegant Heart") to infiltrate a White supremacist group suspected of holding stolen nuclear material, and soon finds himself in the midst of a bank robbery with trigger-happy "brothers".

The team searches for a former Marine and expert sniper who escaped a veterans hospital when they discover his connection to the leader of an extremist group. Also, the case reminds Kensi of her past as a sniper.

Callen and Sam search for answers when they find dead crew members from the missing oil tanker used in Arkady's deal with Russia, and also discover Arkady's personal connection to the ship.