The NCIS headquarters are evacuated after the team discovers a body as well as bomb materials on the roof of the squad room, sending the NCIS team on a race to stop an impending attack while the team also begin reading the first draft of Ducky's upcoming book.
Prologue
Act One
Act Two
Act Three
Act Four
Act Five
Major Events
It's revealed that in the aftermath of the Navy Yard bombing, cell phone jammers were installed.
Trivia
In the episode, Palmer tells Bishop that the windows in the forensics lab are made out of Hermetically-sealed bulletproof glass because of the sniper. This is in reference to Season 3's Premier episode, Kill Ari Part 1 (episode) where Ari Haswari shoots at Abby and Gibbs in the lab.
To add to this, Bishop acts as if she didn't know there was a sniper that attacked Abby’s lab, but in Cabin Fever (episode), she said she knew the story of Ari.