Callen, Kensi, Sam and Deeks go undercover as a elite tactical force to investigate an ambush that's apparently tied to a drug cartel kingpin who has terrorist connections but things take an intense turn when one of the rival training squad members turn up dead, his neck broken during a training exercise with the team soon facing a race against the clock when Nell who had gone in to investigate disappears, leading them to believe that she might have been taken hostage by the killer.