Who can you trust? That's the question on the season finale of 'NCIS' (Tue., 8PM ET on CBS).

[Spoiler alert.]

Gibbs (Mark Harmon) goes down to Mexico to investigate a drug cartel. But there, he finds himself trapped. While trying to investigate the murder of a drug lord that took place nearly 20 years ago, he finds himself caught in a web of suddenly shifting alliances. Gibbs is betrayed by the very people that he trusted -- a brother and sister pair -- and, now he finds himself captured. Will he survive?