Viral is the 6th episode of NCIS Season 13 and the 288th episode of the entire NCIS series.
This episode is also the second episode of the NCIS series to be directed by series regular Rocky Carroll who plays Leon Vance on the show, Carroll having made his directorial debut with the NCIS Season 12 episode, We Build, We Fight (episode).
The NCIS team investigate when the murder of a Navy Petty officer is revealed to match a M.O. that a local serial killer called the Tri-State Sniper is using and it falls to the team to discover if this is the serial killer's latest victim or if it's a copycat killing while McGee and Delilah must learn to compromise before moving in together and potential tragedy lies in store for Bishop.
- The serial killer in the episode appears heavily based off the DC Sniper, a serial and spree killer responsible for shooting random pedestrians with sniper shots and even leaving calling cards behind, such as a tarot card of Death with a message written on it.
|Leroy Jethro Gibbs||Mark Harmon||Special Agent in charge of the NCIS Major Case Response Team.|
|Anthony DiNozzo Junior||Michael Weatherly||Senior Special Agent and second-in-command of the NCIS Major Case Response Team.|
|Timothy McGee||Sean Murray||Special Agent of the NCIS Major Case Response Team.|
|Abigail Sciuto||Pauley Perrette||Chief Forensic Specialist for the NCIS Major Case Response Team.|
|James Palmer||Brian Dietzen||Assistant Medical Examiner for the NCIS Major Case Response Team. Despite being credited, Dietzen does not appear in this episode.|
|Eleanor Bishop||Emily Wickersham||Probationary Special Agent of the NCIS Major Case Response Team.|
|Leon Vance||Rocky Carroll||Director of NCIS.|
|Donald Mallard||David McCallum||Chief Medical Examiner for the NCIS Major Case Response Team.|
|Maureen Cabot||Kelli Williams||NCIS Special Agent.|
|Delilah Fielding||Margo Harshman||McGee's girlfriend.|
|Jake Malloy||Jamie Bamber||Bishop's husband.|
|Roland Ebbakey||Gregory Harrison||Captain in the United States Navy.|
|Nick Rossmore||Brad Benedict||Lieutenant in the United States Navy.|
|Kara Gifford||Kelly Frye||Lieutenant in the United States Navy.|
|Peter Woodruff||Ryan Kennedy||Former Petty Officer First Class in the United States Navy.|
|Dan Campbell||Andrew Hawkes||Detective with the Metro Police Department.|
|Adam Meyers||Dante Swain||Petty Officer Second Class in the United States Navy and the main murder victim as well as Farrah Meyers's brother.|
|Farrah Meyers||Alisha Boe||Navy Petty Officer Second Class Adam Meyers's sister.|
|Jackson Edward||Makabe Ganey||A boy who appears in the episode.|
|Mother (Viral)||Melissa Greenspan||A woman who appears in the episode.|