It's just another day at the New York location of the Counter Terrorist Unit, at that part of the day where smoke fills the air at the high-tech facility.

And no, you're not going to find out why, because in the world of Fox's "24," not knowing what happens in the next minute is all the fun.

At 9 p.m. Sunday and 8 p.m. Monday, the hour-by-hour thriller returns with back-to-back two-hour nights before settling into its regular one-hour Monday slot the next week.

As always, something bad is brewing in the world, and counterterrorist agent Jack Bauer (Kiefer Sutherland) is drawn into the action.

When we last left Bauer, he had saved the nation yet again, at the cost of being infected with a bioengineered disease. As season eight opens, he's recovered, living in New York and hoping to resume a normal life with his family, especially daughter Kim (Elisha Cuthbert).

But an old informant (Benito Martinez, "The Shield") shows up at Bauer's doorstep, and the chase is on to save a vital peace agreement with an Islamic leader (Indian movie star Anil Kapoor). This draws Bauer into contact with an old friend, President Allison Taylor (Cherry Jones), while he makes some new acquaintances at Gotham CTU.

These include its Ivy League-educated director, Brian Hastings (Mykelti Williamson), operations manager agent Cole Ortiz (Freddie Prinze Jr.), and analysts Dana Walsh (Katee Sackhoff) and Arlo Glass (John Boyd).

There are also some familiar faces, such as Jack's FBI partner from last year, Renee Walker (Anne Wersching). And of course, there's Jack's right-hand woman, crack analyst Chloe O'Brian (Mary-Lynn Rajskub). She has returned to work after a long absence and is having a little trouble catching up with the ever-evolving CTU technology.

On this day at the show's sets in the San Fernando Valley area of Los Angeles, a new phase of the crisis has struck at CTU, and Hastings is overseeing the response.

"I am what you call the HNIC," Williamson says, "the 'Head Negro in Charge.' It's actually on my chair out there. I'll have to show it to you. It's pretty cool. Nobody got it the first week."

In the first four episodes, Williamson's character butts heads with both Chloe and Jack. He stands his ground on issues, but as any fan of "24" knows, in the end, he won't win the argument. To Hastings' credit, he rolls with it.

"He doesn't like to lengthen an apology," Williamson says. "No sense in being sappy about it. 'OK, all right, my bad, let's move on.' "

As to what the Hastings-Bauer relationship is, Williamson — who has known Sutherland for a long time and shares a history in rodeo with him — says, "Hastings has heard of Jack Bauer. He's a bit intimidated by him, because he understands that Jack Bauer is a force.

"He's determined to do his business without him, until he realizes that it is just not going to happen. Bauer has so much to contribute that Hastings finally decides that two heads are better than one."

As for how Hastings gets along with Chloe, Williamson says, "Hastings doesn't give Chloe much credit. He tells her he doesn't think it's a matter of intelligence; he just thinks that she doesn't want to do things his way — and he's absolutely right.

"Chloe has her own way of getting it done, and it actually works."

Meanwhile, Chloe has remarried her ex-husband and is now a working mother, but according to Rajskub, there's plenty more change where that came from.

"I really have some major changes for my character," she says, "even more than a child and a husband, I think. Last year, I got some complaints from fans: 'Why don't they do more with you?' I think, this year ... it's going to be interesting to see how people react."

Chloe starts out behind the eight ball, technologically speaking, which is a strange place for someone who is usually the smartest kid in the room — but that's just fine with Rajskub.

"I loved it," she says. "It's my favorite. Did you see the first episode? I think it opens with me bashing on my keyboard with my fist, which you know I love playing. It just gives Chloe an opportunity to hate on everybody."

And if you like Chloe at the beginning of season eight, Rajksub says you're going to just love her by, oh, around episode 19 or so of the 24.

"I'm put in a position to act differently than we've ever seen before," she says. "Toward the end of the season, this is probably the most major turn that my character's taken.

"I don't mean to be so dramatic. I don't turn into an evil monster or anything. It's believable. I'm forced to make some pretty big choices."