When the team investigates a case involving a former marine who is being tracked down by members of al Qaeda for embezzling money from Iraq, Hetty assigns Nell to join Deeks in the field. Meanwhile, Eric is given a new partner in Ops.
When an undercover agent is suspected of working for the smuggler he's supposed to be investigating, the team takes him into custody to find his true intentions. Meanwhile, Kensi and Deeks discuss their personal relationship as Kensi returns to the field.
Sam is convinced that the theft of software for a new unmanned aerial vehicle is connected with the disappearance of the lead engineer's 10-year-old daughter, a girl Sam once provided protection detail for in Saudi Arabia.
When the team and DEA uncover the cartel's plan to slyly transport billions of dollars' worth of cocaine from Columbia to the U.S. using a submarine, Callen and Sam must quickly locate the missing vessel.
The team discovers that one of their own is compromised when they investigate the murder of a navy contractor involved in illegal transactions of confidential data. Meanwhile, Hetty is under investigation in Washington, D.C.