We've seen many finales this TV season, but NCIS saved one of the best for last. It began with unsolved mysteries, answered them, then posed a whole new set of questions.

If "Rule Fifty-One" lacked the panache of past season-enders, it certainly didn't lack for plot intricacy or stellar acting. As Michael Weatherly recently said, it was Gibbs in hell.

Having shaped his character over seven seasons, Mark Harmon has a truly innate and uncanny ability for viewers to understand what he’s thinking without tons of dialogue.

Gibbs is the show's protagonist and a heroic one. Few question him or his personal code. But last night, with his 51st rule - "Sometimes, you're wrong" - he questioned himself.

His inner torment was amazing to watch. Clearly he wasn't going to be turned, no matter what he was blackmailed with, but threats against his loved ones hit close to home.

It would have made sense that Paloma Reynosa wanted Gibbs killed as revenge for his taking Pedro Hernandez's life, but also would've been too easy. She's more calculating.

Also playing a complex game is Alejandro Rivera, who we totally did not peg as a corrupt government official - or Paloma's brother - even though it seems obvious right now.

These two are working Gibbs on both fronts - Rivera wants him tried in a Mexican court, Reynosa wants him working for her, or else she promises to kill everyone he knows.

Vance sent Ziva and Tony to Mexico to rescue Gibbs, only to have him meet them at the airport and hop aboard. No one knows what Gibbs is thinking or doing except Gibbs.

Lt. J.P. Dean ends up dead in D.C. after a shootout with Tony, McGee, and Ziva after his plane touched down, which the cartel let him walk into, having no more use for him.

Vance, who we'll discuss more in a moment, tasked Tony to "follow" Rivera (somehow we doubt "observe and report" was the agenda) in Mexico, but DiNozzo was cornered.

By Mike Franks. Index finger or not, he vows to take it from here, Probie.

As for the Hernandez case, Gibbs refused to have Abby cover up evidence, but someone did step in on his behalf - M. Allison Hart kept the file from reaching Rivera's hands.

In the final scenes of the season, Gibbs sat alone, authoring his 51st rule on an index card, while Reynosa walked into a Pennsylvania store and ominously met Gibbs' dad.

The fate of Gibbs' father serves as the main cliffhanger heading into September, but it's just one of many unresolved issues hanging over us after this very good episode:

• The Hernandez file. Did Hart obtain the only copy? Does Rivera have no record of it? Is the Mexican government never going to bring it up? Can Hart's pull with that government bury it for good? It can't just go away, right?
• Franks, DiNozzo and Rivera. Will Mike take him down, and will there be fallout from the cartel as a result? Was Tony going to kill him before Franks stepped in - and what role will he play in this subplot when the show resumes?
• The package. Was it just a test to see if Gibbs could be trusted, or is there other significance? Did Reynosa expect him to become her inside man at NCIS?
• Reynosa. She really showed up in Pennsylvania to kill Gibbs' father personally? That's an awfully big risk to prove a point. What is her endgame here?
• Vance. How much does he know about what Gibbs is up to, and how involved is he? He says he can make the call to throw Gibbs out, but would he?

This last point was one of the most intriguing elements of "Rule Fifty-One." Tired of looking the other way and being in the dark, Vance had it out with Gibbs over his actions.

Vance has to walk an extremely fine line between letting Gibbs go lone wolf like this and maintaining the chain of command, and clearly that line was blurred in this case.

It's hard to tell to what degree Vance feigns anger at Gibbs, the extent to which he's aware of what's going on, or what his own agenda is ... he's got a good poker face himself.

Rocky Carroll is always terrific in any case, and the Vance-Gibbs relationship is one we'd like to see explored in even greater depth. The old movie references were great, too.

Overall, it was a strong conclusion to the season, and certainly gives us plenty to discuss all summer. Oh, special congratulations go out to Ziva for becoming a U.S. citizen!

What did you think of last night's NCIS season finale? Do you have theories on any of the questions above (or your own questions)? Share your comments!

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.