So it turns out Director Vance (Rocky Carroll) split up Gibbs's team to ferret out NCIS's involvement in the theft of military secrets. The three members of Gibbs's new team are all suspects, and McGee, DiNozzo, and David each play a role in unmasking the traitor. The catch, classically revealed in the final seconds of the premiere, is they don't succeed. This sets up some nice suspense for the season.
Kudos to writer-showrunner Shane Brennan.