It all started when Earl Goddard from Homeland Operations tried to rope her into a practice exercise to see how easy it would be to execute a terrorist act at an arena concert (which, by the way, was frighteningly easy). Abby is pretty reluctant, having turned him down some 20 times, but is overruled when Vance (Rocky Carroll) made it a direct order. As she feared, Abby got super into planning this thing, tapping into her Evil Abby alter ego and helping pull off the sick idea of simulating sarin gas drops in balloons, placed in the vents, to kill hundreds in the venue (Scared yet?) The only hitch: Abby is nabbed by officers who quickly realize her fake bombs and simulated gas weren't fake at all, and she suddenly looks like the mastermind of a horrible crime.Earl, of course, could explain everything expect for one small detail: he turns up apparently murdered, deepening the mystery.
Naturally, the members of Earl's think tank -- the annoyingly English actor JJ, Greta from the CDD and another expert, Phil -- are under serious suspicion; even Leon Vance (Rocky Carroll) and Gibbs' (Mark Harmon) confidence in Abby begins to erode as they try to piece together what happened.
Once the think tank members are cleared, suspicion turns to Homeland Operation's leader Knox who had some really shaky excuses for his whereabouts and why he wiped clean his computer around the same time Earl's access had been compromised too. Knox finally cops to having been hacked and with McGee's (Sean Murray) help, all signs point to New Orleans, where somebody has dug into that situational playbook to figure out exactly how the government would respond in the event of terrorist catastrophes. Torres (Wilmer Valderrama) steps up to the plate, volunteering his services to dig deep in his network from his undercover days; meanwhile, Ellie Bishop's (Emily Wickersham) sleuthing helps reveal that Earl's entire operation was a fraud.
Somebody set him up to execute this needless drill, and when Alex Quinn (Jennifer Esposito) ) and Abby put their heads together, it's clear there was a very specific target for the attack: a Serb with involvement in the Bosnian War. Aha! It's the missing link that helps them find the connection that was right under their noses -- Phil, the member of the think tank who admitted to losing his parents in that war previously. Phil wanted revenge and he used poor Earl, a man he said was like a father to him, to get it done.
Earl caught on though, but it was too late: Phil killed him. Not before he heroically set off a silent alarm though, which is how Abby caught the attention of authorities. What a guy! That still doesn't solve the the issue of the missing Homeland Security playbook though, and when Torres realizes one of his old figures Ferdinand Pisco (Jessy Leros) from his shadowy days is en route to New Orleans to buy it, Gibbs sends him down South -- with McGee keeping close watch.