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.
During an NCIS hit-and-run investigation, Palmer joins a stranger on the outside ledge of a building in an attempt to save his life.
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.
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.
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.
The FBI and M16 continue their international manhunt as the escaped British spy leaves one agent fighting for his life in the ICU.
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.
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.