A series of events that occurred in 2003:
- Lieutenant Loren Singer returns to Washington D.C. and meets with Theodore Lindsey. At some point, the two get into an argument that ends when Singer slips and hits her head on the railing. Lindsey thinks of calling for an ambulance but later changes his mind and subsequently drops Singer into the river where she drowns seconds later. Her remains eventually land in a tree where they stay there for the next three months with crows peeling away at the flesh, leaving a badly disfigured face. The remains then wash up in a tree in a Potomac Park.
- Singer's remains are discovered in a tree in Potomac Park by a young scout boy. When the NCIS team arrive to investigate, they discover that it's a female JAG Lieutenant with the DNA match revealing that the remains are those of Lieutenant Loren Singer, prompting a murder investigation to be launched.
- NCIS successfully capture terrorist Amad Bin Atwad.
- NCIS later arrest JAG Commander Harm Rabb Jr. after Harm emerges as the prime suspect into the investigation into Singer's murder and also of the overwhelming evidence against Harm.
- During the investigation into Lieutenant Singer's murder, NCIS Special Agent Leroy Jethro Gibbs is given the task of interrogating Bin Atwad so that NCIS can obtain information on a possible terrorist attack.
- As Gibbs leaves to interrogate Bin Atwad, the members of both NCIS and JAG testify in Harm's trial.
- Gibbs's colleagues, NCIS Special Agents Anthony DiNozzo and Vivian Blackadder soon discover evidence confirming that Rabb is being framed for Lieutenant Singer's murder. They soon arrest the true murderer- disgraced JAG commander, Theodore Lindsey with Lindsey eventually pleading out in to involuntary manslaughter while Lindsey gets eight years in Leavenworth while the charges against Harm are subsequently dropped.
- Tony and Viv head to Rota, Spain and participate in stopping Hussan Mohammed and his men carry out another terrorist attack. They along with Gibbs and the Spanish Police engage in a gunfight against the terrorists while Mohammed is killed when Gibbs shoots him. However, although the operation is considered a success due to the majority of terrorists either dead or in police custody, Gibbs expresses anger towards Viv for blowing the operation.
- After the operation, the NCIS team presumably return to the United States where Viv is presumably forced to resign from NCIS as a result of her actions in the operation or she is sent back to the FBI by mutual agreement, terminating her employment with NCIS.
- With Viv no longer a member of the team, Gibbs and Tony become the two acting NCIS Special Agents for the NCIS Major Case Response Team, a trait that continues from April 2003 to September 2003.
- After a Navy Commander dies on Air Force One, Gibbs and Tony travel to the crime scene and meet Secret Service agent Caitlin Todd as well as FBI agent Tobias Fornell.
- Following the Air Force One Incident, Kate resigns from the Secret Service for good and joins NCIS, subsequently becoming an NCIS Special Agent and also Vivian Blackadder's replacement.
- Kate begins her career as an NCIS Special Agent.
- The team travel to the Norfolk Naval Base where they meet NCIS Special Agent Timothy McGee.
- The team later head to Guantanamo Bay aka "Gitmo" where they're introduced to fellow NCIS Special Agent Paula Cassidy.
- April 22, 2003- Ice Queen (episode) airs for the first time.
- April 29, 2003- Meltdown (episode) airs for the first time.
- September 23, 2003- Yankee White (episode), the NCIS Season 1 premiere episode and also the first episode of NCIS as a solo series airs for the first time. NCIS itself also begins broadcasting as a lone series under the title "Navy NCIS".
- September 30, 2003- Hung Out to Dry (episode) airs for the first time.
- October 7, 2003- Seadog (episode) airs for the first time.
- October 14, 2003- The Immortals (episode) airs for the first time.
- October 28, 2003- The Curse (episode) airs for the first time.
- November 4, 2003- High Seas (episode) airs for the first time.
- November 18, 2003- Sub Rosa (episode) airs for the first time.
- November 25, 2003- Minimum Security (episode) airs for the first time.
- December 16, 2003- Marine Down (episode) airs for the first time.