The team investigates a car explosion with a connection to an agent who went missing six months earlier; Gibbs asks NCIS Special Agent Alex Quinn to shadow his team.
While investigating a murder at a Quantico reunion, the NCIS team uncovers a bomb plot and a long-running theft ring; Torres and Quinn adapt to their new lives on Gibbs' team.
When a Marine falls to her death, the woman's doctor (Laura San Giacomo) tells Gibbs that she thinks the woman was murdered.
The body of a navy lieutenant is discovered aboard a destroyer while civilian guests are allowed to spend the night on the ship; McGee considers the perfect proposal for Delilah.
When a missing M16 officer is linked to the death of a petty officer, Gibbs sends Quinn and Bishop to investigate; Quinn recounts a painful ordeal that caused her to leave field work.
Torres breaks protocol when he learns that a witness in an NCIS case is wanted by U.S. Immigration and Customs Enforcement; Abby, Bishop and McGee try to woo Tony DiNozzo Sr. to sublet Tony's old apartment.
Agent Bishop questions her previous work at the NSA after being sent to Gitmo to gather evidence for a Navy chaplain murder case; Bishop's brothers visit for Thanksgiving.
The team looks into a series of threats against congresswoman Jenna Flemming; Director Vance takes charge of temporary protection detail.
An operation to catch a businessman who is using acts of terror to manipulate the stock market is compromised, forcing the NCIS team to search for new leads.
When Gibbs identifies the brother of an NCIS most-wanted suspect, he goes under cover to penetrate their anti-government militia; Bishop and Reeves team up for a clandestine investigation.
The murder of a petty officer in a small town outside D.C. prompts NCIS to once again work with The Sherlocks, a privately funded investigative team.
Abby is found in possession of a real bomb after her homeland security think tank is compromised; a theoretical terror playbook is stolen and is being auctioned on the black market.
Bishop is determined to get revenge for the murder of her late boyfriend, Qasim, after Gibbs and the team find a new lead in the Chen case; Torres teaches the agents the art of pickpocketing.
McGee finds his apartment torn apart by a robber trying to locate a valuable item hidden there by the convicted criminal who previously owned the unit; Congresswoman Flemming encourages Vance to pursue a career in politics.
To carry out a sailor's dying wish, Gibbs and the NCIS team re-investigate a murder case that was originally ruled an accidental death.
A seaman who was prepared to testify before a grand jury is murdered, which leads the team to discover the resurgence of an international human trafficking ring; a storm causes power outages all over the city.
An unusual investigation takes place when the body of a murdered deep-sea diver and his suspected co-workers must stay in a decompression chamber for four days.
Secretary of the Navy Sarah Porter's daughter is kidnapped; NCIS Special Agent Valerie Page, McGee's childhood friend, assists the team with advance tactics training.
Dr. Cyril Taft finds key evidence when he is assigned to surgical duty for a suspect.
Personal plans are interrupted when errors are found in what seemed to be a straight-forward, closed case; McGee and Delilah argue whether work should be discussed during dinner.
After an American couple is attacked in Iraq, Gibbs questions the lone survivor of a Special Ops group that was attacked months earlier in the same area.
When a Navy officer is murdered, the team must determine whether the man's wife or mistress is lying; a homeless woman believes Anthony DiNozzo Sr. is her father.
After Special Agent DiNozzo's identity is stolen, the perpetrators use his name to begin blackmailing senators.
NCIS teams up with the FBI and Homeland Security to pursue two escaped British prisoners, one of them a former spy, who have crossed international borders.
Gibbs suspects that a 14-year-old who stopped a home invasion is holding back information; Vance and Fornell head to London as part of the case involving the escaped British spy.
NCIS, FBI and MI6 continue the worldwide manhunt for a British spy who is targeting current and former agents.
Following the bombing of NCIS headquarters, the team engages in a cross-agency manhunt for Harper Dearing.
The team investigates when the body of an NCIS facilities manager is found four months after she went missing; as the team faces mandatory psych evaluations, Gibbs is concerned about Abby's recurring nightmares.
Two mercenaries are found dead on Gibbs' boat; Gibbs must consider his former mentor in a new light.
Gibbs goes to Mexico to confront a drug cartel intent on revenge; Gibbs has to make a devastating decision.
When a Marine's wife kills the intruder who tried to rape her, Gibbs and his team realize they are tracking a serial rapist and killer who uses a racy Web site to stalk his prey.
Tony goes under cover as an escaped prisoner chained to a convict who holds the key to recovering stolen Iraqi art, but when his GPS device fails, the team must find other ways to locate him.
Gibbs and the NCIS team work with a notorious private detective during an investigation of a naval officer found murdered at the bottom of a lake.
The team investigates a telemarketer's report of the murder of a petty officer after hearing it over the phone, and it appears to be a hoax until the body of the officer is found.
When bodies found stuffed in a barrel are identified as a prosecutor and a sheriff who worked on a rape and murder case with Ducky 10 years ago, Gibbs believes Ducky may be the next target.