Thomas Gibson, Joe Mantegna and Shemar Moore

On the Criminal Minds Season 6 premiere, Agent Morgan will cross a very personal line in order to save a young girl's life.

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Morgan (Shemar Moore) not only has to catch a serial killer (guest star Tim Curry) during a Los Angeles blackout, but he's also driven by a promise to protect the daughter of Detective Spicer (guest star Eric Close), who was murdered in the Season 5 finale.

"We wanted to put a lot of weight on Morgan," executive producer Simon Mirren says. "He's personally invested because in the cliff-hanger, he witnessed this awful thing. He's never had to make a promise before. He's a single guy because of the life he leads and he doesn't want to put that kind of pressure on anybody or to have any demands on him. His teammates feel maybe he's crossing a line, but after what he's witnessed, the lines aren't blurry anymore."

Because of his promise, Morgan will lead the team's efforts to track down Curry's character, which proves to be no easy feat. "With a blackout, what do you do?" Mirren asks. "It's sheer chaos, and this serial killer is using that. The team members have to use their own initiative and figure out the best way to get the guy's attention. They end up relying on an emergency radio frequency to manipulate the situation and get ahead of this killer."

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Regardless of what happens in the premiere, Morgan's vow will continue to play out over the first part of the season. "It's actually an arc that we're going to follow for a few episodes," he says. "We don't normally do arcs, but we felt that in the sixth season we could maybe go a little further into our main cast's lives."

That also means will be seeing more of Spicer's daughter, which allows Morgan and single father Hotch (Thomas Gibson) to bond. "There's a very wonderful story ... that involves the little girl from last year and my family and Agent Morgan's connection with the little girl," Gibson says. "All of those threads are brought together ... and intertwine in a really great way." Mirren adds: "Hotch is now a single father and Morgan is trying to be a father figure. So it's about how Hotch can offer Morgan, in an adapted way, advice about those things."

Gibson says he's looking forward to Hotch interacting more with his son, Jack, who remains Hotch's one bright spot after the murder of his ex-wife Haley. "Everything is as good as it can be under the circumstances with Jack," Gibson says. "It's a very difficult balancing act that Hotch has got himself in. ... Having his son is kind of what he's wrapping most of his optimism around. Hopefully we can find some other reasons to lighten up a bit."

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Perhaps another woman? "I imagine he's not going to completely shut down the idea of finding somebody again, but it's hard," Gibson says. "We're trying to be respectful of what has happened. He's just drawing himself into the work so completely that he doesn't have the time to reflect or even to mourn."

All of the characters' personal lives will be explored more fully this season, as each team member will have a major secret revealed to his or her colleagues, Mirren says. "Some of them are very emotional, and some of them are very simple," he says. "They are things that they have held to themselves outside of the dark job that they share."

As expected, the secrets will present the team with some challenges. "When you find out something about someone you thought you knew, it can be, on the one hand, a really impressive thing that offers a whole different kind of perspective," Gibson says. "At the same time, it could possibly undermine the relationship and cause conflict or some sort of mistrust. ... I think audiences are going to find them interesting. They're going to be organic to the characters and things that will have made sense all along."

Criminal Minds
returns Wednesday at 9/8c on CBS.