Mark Harmon Mark Harmon

The uncovering of skeletons from Jethro Gibbs' past left his father in danger in NCIS' Season 7 finale. As Season 8 begins, everyone close to Gibbs may have a target on his or her back.

Executive producer Shane Brennan tells that Gibbs Sr. (guest star Ralph Waite) will be front-and-center through the first episode and that his actions will give viewers an idea where Gibbs (Mark Harmon) gets his fighting spirit.

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"It's a big opening," Brennan says. "I advise every fan of the show to sit down and watch that first minute. It's explosive. We finish up that story, and we'll get back into showing NCIS as the team it's always been."The bad news, however, is that Gibbs' team members feel threatened when their investigation of a helicopter pilot' murder leads Gibbs back to the vengeful Paloma Reynosa (Jacqueline Obradors

), whose father Gibbs killed. Worse still, not every team member takes the news of Gibb's murderous past with a smile."I think that DiNozzo is squarely confronting several personal demons this year," Michael Weatherly says of his character. "You see a man who is a maybe a little less silly. He's not totally lost his sense of humor, but I think there are some changes going on with that character that are kind of a subsequent result of seeing Gibbs in a new light."

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Expect deeper insights into several characters this season, as Brennan promises origin episodes for at least a couple characters. Plus, look for the return of Ziva's father (Michael Nouri) to lead to what Brennan calls this season's first big Tony-Ziva (Cote de Pablo) moment."For Tiva fans, there is a moment in the first half of the season," Brennan says. "There will be some ghosts from the past, though maybe some of them are not ghosts. It probably won't go as far as [the fans] want it to, but have we ever gone far enough for them?"Gibbs' relationship with Abby (Pauley Perrette), meanwhile, should settle down, even though she was the first to uncover Gibbs dark secret. "It's a complex relationship and we've just added another layer of complexity," Brennan says. "But we would not jeopardize the relationship that the audience has come to love. It does bring a different perspective to it, but it's not like they're going to be busted up. Gibbs and Abby are going back to being Gibbs and Abby."

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But Brennan, who's known for meticulously plotting out his seasons far in advance, is already thinking about the season's end. And it sounds like the NCIS team may not stay very peaceful for very long."Toward the end of the season, there will be a big, big, enormous question mark over one of the characters," Brennan teases.NCIS returns Tuesday at 8/7c on CBS.