LOS ANGELES (AP) – Surprise is what makes “24” tick, and there should be plenty of it as Jack Bauer embarks on a fourth season of saving the world from terrorists.

Or maybe this time he won’t. With Agent Bauer, played by Kiefer Sutherland, you can never be sure.

“There’s a sort of roiling internal conflict put into the body of a hero,” says executive producer Evan Katz, describing Bauer’s “dark corners” as being more traditional for a villain. “You’re not sure what he will do, not sure how far he will go.”

Last season, Bauer shot up heroin, cut off the arm of his Counter Terrorist Unit partner, shot a man in custody to get him to hand over information more quickly and threatened to expose a terrorist’s daughter to a deadly virus, just to name a few. But he also saved the world from that killer virus.

This season, set 18 months later, Bauer has kicked his drug habit. Booted out of CTU, he has a new job working for Secretary of Defense James Heller, played by William Devane.

Most of the series’ previous villains, including President David Palmer’s scheming wife, Sherry, are no more. Gone too, at least for now, are cast members Dennis Haysbert, who portrayed Palmer for three seasons, and Elisha Cuthbert, who played Bauer’s constantly imperiled daughter, Kim.

Palmer decided not to run for re-election after the death of his evil wife. Katz would not discuss where Kim went, although both characters are still alive and therefore could return at any time.

Fox is premiering the new season of “24” as a “2”-day, “4”-hour event, Sunday, Jan. 9, and Monday, Jan. 10, 8-10 p.m. ET. Then, beginning Jan. 17, the remaining hour-long episodes – each consisting of an hour in the life of Bauer – will air Mondays at 9 p.m. without repeats or pre-emptions.

New this season, along with veteran character actor Devane, are Kim Raver as Heller’s daughter and Bauer’s new love interest, Audrey, and Alberta Watson as CTU chief Erin Driscoll, who of course totally disapproves of Bauer.

There are also spanking new CTU headquarters and a whole slew of new villains, including Nestor Serrano and Shohreh Aghdashloo (Oscar-nominated for 2003’s “The House of Sand and Fog”) as a Middle Eastern husband and wife plotting something dastardly.

“There’s no question there are more wholesale changes than usual,” Katz said.

He noted the story lines involving President Palmer and Kim Bauer had “run their course” and that “catching the audience by surprise” remains a critical element of the series.

Not wanting to give away those surprises, Katz can’t offer much elaboration. He does say the new season – “Day 4” as it’s called, because each season covers 24 hours – will be “big emotionally,” but that it’s important to avoid making the action too fanciful – like over-the-top James Bond-style thrillers.

It’s vital for the tension of the series that “it stay true to the real-time format,” Katz explains. Yet that can be a challenge to the show’s authenticity, particularly because the action takes place in Los Angeles, where traffic can be snarled around the clock.

“We stretch things as much as we can. We have helicopters and, don’t forget, we count the time in commercial breaks,” laughs Katz, whose previous credits include the quirky monster-chasing series “Special Unit 2,” which aired on UPN several years ago.

The new CTU headquarters set – an elaborate, multistory maze of steel, glass and concrete with splashes of peacock blue and ruby red brightening its sleek design – looks like something any Bond movie would be proud to feature.

On this day, Raver’s Audrey was challenging the methods and motivations of the CTU staff, while Devane waited off-camera for a later scene.

Wry and tough, Devane has the perfect manner for someone who’s not supposed to give too much away.

“I’m the kind of secretary of defense the country needs,” is about all he’d say about his character.

Devane’s take on the plot?

“Jack works for me. I have a daughter who’s my aide, and son who’s kind of a hippie guy. We came to L.A. for something – I forget what – and all hell breaks loose and Jack takes charge.”

He grins. “That’s the one thing I’ve learned: Jack takes charge and he gets it done!”