Dominic Vail appeared in a total of 14 episodes. For all his appearances, see List of Appearances.
Agent Vail was introduced in the episode "Identity" as the team's rookie agent. He was originally partnered with Kensi Blye.
Dom was not a native of Los Angeles. An MIT alumnus, Dom moved to straight to LA after he was recruited by NCIS following graduation.
Dom's field of study was not disclosed, although on several occasions he demonstrated advanced skills with computers and electronics, and a tech guy named Ty stated that he "makes a pretty good geek for a field agent."
As of season 1, both of Dom's parents were still alive. Dom was an uncle, as evidenced by crayon drawings stuck to his refrigerator door.
Dom disappeared in the episode "Past Lives" (although his team did not realize this until the following episode "Missing") and was finally found in the episode "Found". It was revealed that he had been captured by professional kidnappers hired by Islamic militants and held hostage in the hope of facilitating a prisoner exchange.
Although agents Callen, Kensi and Sam eventually found him after one of the terrorists, who was Moe, secretly gave him the handcuff key in his food, they later found themselves caught up in a major gunfight with the terrorists.
While pinned down on the rooftop, Dom spotted another terrorist and screaming Sam's name, rushed into the line of fire, taking the hit, essentially sacrificing himself to save Sam's life before falling to the ground, bleeding and suffering fatal injuries.
Sam dragged Dom to safety before he finished off the first terrorist while Kensi shot the second terrorist and Callen posing as one of Kalil Abramson men's shot Abramson before he and Sam rushed to Dom's aid.
Despite Sam and Callen's efforts to stop the bleeding, Dom died almost immediately with his death leaving the OSP team completely shell-shocked and grief-stricken.
In the aftermath of the tragedy, Sam and Kensi were seen crying while in the office, the majority of the OSP team watched in disbelief as the events unfolded before them. Hetty left the Ops Centre, distraught and later attempted to resign from being the Operations Manager in the next episode, Hunted but thanks to Callen recovering her resignation letter from Vance, she stayed on.
Dom's role in the team and his position as Kensi's partner was later taken over by LAPD Detective Marty Deeks.