The team tries to find Callen and Sam, who are trapped in a submarine set by terrorists to hit an aircraft carrier in San Diego; against orders, Hetty forgoes her trip to Washington.
As CSI members investigate the murder of a Navy contractor involved with selling confidential data, they find that one of their own is compromised.
A member of the team is targeted by the Department of Justice; Hetty receives disturbing news from Director Leon Vance.
A desperate search begins when the team learns that one of their own is being targeted; Nate Getz tries to help Nell recover from her traumatic experience.
After a shooting at the Department of Defense, Callen and Sam go to Mexico to hunt for the only employee who managed to escape.
Callen and Granger try to clear Sam's name after he's arrested for a woman's murder; Kensi and Deeks find a link between the victim and Sam's past.
The team suspects a terrorist group is responsible when a man is murdered by a small drone; Nell tries to avoid disaster in Long Beach.
When Deeks and Kensi go under cover to investigate the murder of a homeless man -- who used to be a Marine and CIA agent -- they find a connection to a Mexican cartel.
Eric becomes one of seven suspects when Granger is poisoned by the mole; Hetty institutes a lockdown during the investigation.
The team launches an investigation into the murders of Marines whose sons are in military academics; Sam reflects on his upbringing and his relationship with his dad.
As the team investigates a burglary at a cybersecurity company, Hetty reveals that Callen's girlfriend is a lead witness; members of the team discuss their holiday plans.
The undercover investigation of an arms dealer is interrupted when terrorists take over the suspect's office building and Callen is taken hostage.
Sam and Callen are sent to retrieve key evidence after a U.S. Ambassador (Julie Chen) narrowly escapes a terrorist attack.
In hope of identifying the source of an anthrax poisoning before it can be used as a weapon, Sam and Callen go under cover as food truck owners.
Callen and Sam are abducted during their pursuit of an anonymous tip about a missing NSA agent; the team thinks Callen and Sam fell victim to a trap set by terrorists.
When Sam is shot by a spy contracted by the CIA the team enlists the help of a Nepali soldier to help find the shooter; Kensi and Deeks have an argument.
As members of the team investigate the death of an Afghanistan soldier training in the U.S., they find two other soldiers are missing; Sam is back on the team but some wonder if he is ready.
After a successful sting, an explosion claims the lives of three FBI agents; Kensi and Deeks realize their secret is out.
The team searches for those responsible when a missile test is hijacked; a young computer specialist assists the team.
Callen and Sam go back to their undercover identities as a prisoner and a guard to get inside a white supremacist group that might have stolen nuclear material; Kensi poses as Callen's girlfriend; Callen and Hetty's first meeting is revealed.
A former acquaintance -- presumed to be a murder victim -- makes a shocking reappearance to ask Callen and Sam for help.
The team looks for an unstable former Marine -- who is an expert sniper -- when his connection to an extremist group is revealed; Kensi is reminded of her past.
Dead crew members turn up from the missing tanker involved in Arkady's deal with Russia; Arkady's connection to the ship is revealed.