Ari language (New Guinea), a Papuan language of the TransNew Guinea family
Ari language (Ethiopia), an Omotic language of Ethiopia
Ari (Abiji) language, a Kwa language of Ivory Coast
ari, ISO 639-3 code for the Arikara language, spoken by the Arikara people, mainly in North Dakota
An abbreviation for Aries (constellation), as standardized by the International Astronomical Union
Ari-Motorfahrzeugbau GmbH, German automobile company, which in the 1920s manufactured the Arimofa and the two-stroke Ari motorcycle
Average recurrence interval or return period, an estimate of the likelihood of an event, used in hydrology, water resources, meteorology, etc.
ARI, Chacalluta International Airport in Arica, Chile (IATA code)
Aberdeen Royal Infirmary, a tertiary referral hospital in Aberdeen, Scotland
Acoustics Research Institute of the Austrian Academy of Sciences
Acute respiratory infection
Added Reality Interface, a fictional piece of technology in the video game Heavy Rain
Adjusted Rand Index, a clustering metric
Alternative for a Republic of Equals, now known as Civic Coalition ARI, a political party in Argentina
Alternative Routing-ID Interpretation, an extension to the PCI Express computer input/output standard that supports the virtual machine computing model
American Refrigerant Institute, a trade association in North America
Angel Resource Institute
Arthur Rylah Institute for Environmental Research, an organization conducting environmental research in Victoria, Australia
Associazione Radioamatori Italiani, an amateur radio organization in Italy
Astronomisches Rechen-Institut, an institute based in Heidelberg, Germany
Astrophysics Research Institute at Liverpool John Moores University, England
Autism Research Institute, an autism-related organization
Autofahrer-Rundfunk-Informationssystem, a system formerly used in Germany to indicate traffic announcements on FM radio broadcasts
Automated Readability Index, a readability algorithm
Avicenna Research Institute, an Iranian biotechnology research institute
Ayn Rand Institute, an organization devoted to exposition of Ayn Rand's philosophy, Objectivism
ARI by Ariana Grande, Ariana Grande's debut fragrance
The "Kill Ari" story arc centers on Gibbs' hunt for Ari Haswari, who shot and killed Special Agent Kate Todd in the second season finale of NCIS. It also introduces two new main characters to the showMossad Officer Ziva David and NCIS Director Jenny Shepard. Due to these changes in the cast, Bellisario labeled the third season as "the season of change".
The episode opens with a recap of the second season's finale, "Twilight": as the NCIS team by Leroy Jethro Gibbs (Mark Harmon) engage in a gunfight against Ari Haswari's terrorist cell, Ari (Rudolf Martin), identified as a rogue terrorist, attempts to kill various NCIS agents including Tim McGee (Sean Murray) before Ari decides to fatally shoot NCIS Agent Kate Todd (Sasha Alexander) with a long range sniper shot, killing her instantly with a horrified Gibbs and Tony DiNozzo (Michael Weatherly) witnessing Kate's death. In the aftermath of the murder, the team struggles to come to terms with her death while an enraged Gibbs seeks revenge against Ari. Shortly afterwards, Ari attacks again, firing at Abby in her lab. However, she survives physically unharmed.
Then NCIS Director Tom Morrow (Alan Dale) announces that he is leaving the agency after receiving a job offer from Homeland Security and introduces Jenny Shepard (Lauren Holly) as his replacement. It immediately becomes apparent that Gibbs was romantically involved with Shepard while working undercover with her years earlier, though she insists that she is now nothing more than his boss and will act accordingly. Gibbs clashes with Shepard, who believes that Ari Haswari was not the one responsible for firing the bullet that killed Agent Todd due to the fact that there's no physical evidence or proof of any kind linking him to the crime.
Ziva David (Cote de Pablo), Ari's Mossad control officer, arrives shortly afterwards. She sides with the director and further weakens Gibbs' case, claiming that Ari is completely innocent and offering evidence to support her assertion. However, Ziva's motives for defending Ari become ambiguous when she communicates with him without informing anyone in the NCIS office and her conversation indicates a personal connection to him.
Gibbs realizes that Ziva has contacted Ari and orders DiNozzo to tail her. Ari later returns, taking Gerald Jackson (Pancho Demmings) hostage, though he quickly notifies Ducky to divert the team's attention away from Ziva and force Ducky into a meet.
The episode ends with Ducky approaching the pre-arranged meeting point, unaware that Ari has a sniper-rifle trained on him.