'NCIS': 11 Game Changers

''The Curse'' (season 1, episode 5)

Five episodes into its run, NCIS set itself apart from the crowded field of by-the-numbers crime-solving TV, says star Michael Weatherly. How? A simple head slap. ''I think that was a game changer because it became part of why the show was different from Without a Trace or CSI or Cold Case or any of the procedural dramas that existed at that time, 2003. What it really came down to was character.''

''Twilight'' (season 2, episode 23)

The death of Sasha Alexander's Caitlin Todd rocked the team and is still talked about today in circles of fans as one of the show's most shocking moments. Weatherly says, ''It told the audience to expect the unexpected.'' ''For a show that gets criticized by some as being geriatric or tending to an older demographic, that's a pretty shocking moment.''

''Kill Ari'' (season 3, episodes 1 & 2)

After Kate's death there was a desk that needed to be filled. ''Enter Ziva,'' says Weatherly. ''She saves Gibbs' (Mark Harmon) life and earns the trust of Gibbs and becomes a deeply curious human being that DiNozzo sits across from.'' And so began the ''Tiva'' years.

''Requiem'' (season 5, episode 7)

The importance of ''Requiem'' goes beyond what viewers saw on the screen, says Weatherly. To him, it represents the action the show was experiencing behind the scenes, too. At the time, exec producer Shane Brennan was five episodes into his first year as captain of the ship, the writer's strike had just put the TV season into limbo, and season 5 was the year NCIS entered the top 5 in ratings for the first time. ''All kinds of things were exploding, and so this episode sits smack dab in the middle of all of that,'' Weatherly says. All that said, the hour itself — the first for longtime NCIS director Tony Wharmby — also had a few memorable moments. ''It's when DiNozzo gives Gibbs mouth-to-mouth resuscitation,'' Weatherly remembers, with a laugh.

''Judgment Day: Part 1'' and ''Part 2'' (season 5, episodes 18 & 19)

Another death. Another shocking moment that left the team — and viewers — reeling. ''That was a shocking change and no one saw that coming,'' he says. Five months prior to this episode's airing, NCIS also began airing in syndication on the USA Network, which ''created a whole new audience for the show,'' says Weatherly.

''Last Man Standing'' (season 6, episode 1)

With the start of season 6 came the integration of director Vance (who replaced Holly's Jenny Shepard). Weatherly says the show welcomed ''the Rocky Carroll feeling.'' ''Suddenly director Vance became a big thing and we all knew big changes were afoot,'' he says. Big changes came behind the scenes, too. ''The syndication had been going all summer and I think we became the No. 2 scripted show that year.''

''Legends: Part 1'' and ''Part 2'' (season 6, episodes 22 & 23)

NCIS itself was a spin-off of long-running drama JAG, but when the former became a huge success, the natural next step was to look at further growth possibilities. For this season 6 two-parter, Chris O'Donnell and LL Cool J introduced viewers to G. Callen and Sam Hanna, respectively, who went on to helm NCIS: Los Angeles. ''This show became a franchise all of a sudden,'' remembers Weatherly.

''Truth or Consequences'' (season 7, episode 1)

Though the show had been in syndication for almost two years by the start of season 7, Weatherly says he felt a shift in 2009. ''This is the first season that some people came to the show,'' he says of the season opener, which found Tony captured in Africa and dosed with truth serum by terrorist Saleem Ulman (Omid Abtahi). '''Truth or Consequences' was sort of a good primer [for new viewers]. It introduced the whole team through Tony's eyes,'' he says.

''Shabbat Shalom'' (season 10, episode 11)

''Nobody does that in the middle of the season,'' Weatherly says of the deaths of Ziva's dad, Eli David (Michael Nouri), and Vance's wife, Jackie (Paula Newsome). ''And I think what was nice about that last year is that Gary Glasberg showed us that what we've seen so far is just the tip of the Glasberg. And there's great hidden depths and more in our bag of tricks.''

''Past, Present, and Future'' (season 11, episode 2)

''I think Gary summed it up in the letter?it's a game-changer,'' Weatherly says of Ziva's final episode, airing Oct. 1. ''We, at first, had to sort of absorb it, and then I think we're all really surprised at how durable this show is. I guess maybe we shouldn't be surprised. As we've seen, there have been a lot of changes of the years, and it's something this show handles very well.''

(Season 11, episode 9)

Episode 9 will mark the introduction of Ziva's successor, played by Sopranos actress Emily Wickersham. ''We've got a new ingredient,'' says Weatherly, who says he has full confidence that the addition of Wickersham's Bishop will be handled with care. Why? It's directed by Dennis Smith, ''who did Ziva David's first episode.'' Weatherly adds, ''I think the fans are going to like that they are in safe hands with Mr. Smith.''