With two episodes in production at any one time, a huge cast, overlapping storylines, large action sequences and relentless forward motion, the crew members of Fox's "24," currently airing its sixth season, have set the bar very high for themselves.

"I wish I could tell you in detail how we do it, then I could market it and make money out of it," says producer and director Jon Cassar, who worked on two episodes in season one and has been with the show full time ever since. "I don't know how we do it, honestly. The people I've got around me are so experienced.

"We have an amazing crew. They've been with us pretty well for the duration, so they know the game. That's the reason they're still here. There are some people who aren't with us anymore, who didn't give that 100 percent that we need to make this show. These people, this is the way they are."

Fox also now broadcasts the hour-by-hour adventures of world-saving counter-terrorist agent Jack Bauer (Kiefer Sutherland) in high definition (for those with HDTVs, who receive HD signals over the air or on cable or satellite).

While the demands of HD's crystal clarity and precise detail add to the workload, Cassar thinks it's worth it.

"For me, as a director," he says, "I'm ecstatic that people get to see the show the way we get to see it. I can't even watch anything but HD now. It's fantastic. It's night and day. You can't even make the comparison."

Asked if the show plans to switch from its current 35mm film format to shooting on high-definition videotape, Cassar says, "There's been that talk, but unfortunately, the range isn't quite where we need it. Digital needs a little more control. Film's a little more forgiving when you're working in different light sources.

"In our world, when we're outside, that's our biggest problem. When we're doing daylight exteriors, sometimes we just go with whatever the sun's doing. You can't do that in the HD world. You've got to control it. That would lose too much time for us. We move too quick."

But that doesn't mean that the occasional bit of videotape hasn't snuck in.

"We've tested it," Cassar says. "You just don't know it. We shot the finale of the season four, on the rooftop, with the helicopters — the whole sequence, one of the cameras was an HD camera, and it was right beside the 35mm. We cut it together, and no one knew."

Whatever its production hardships, keeping the story varied and moving is an even bigger challenge.

With a seventh season looming, "24" will have to come up with a new threat facing the nation. In the past, there have been Middle Eastern extremists, Russian rebels, Mexican drug lords, angry Chinese (Jack did kill someone in their embassy) and individual bad folks of all sorts.

"We are absolutely evenly employing all the bad guys of all nations," Cassar says. "Some told me, because I'm Canadian, they said, 'Hey, why are you leaving us out? Why can't we be the bad guys?' I'm like, 'Good idea. Quebec separatists could be the terrorists.'

"I'd like to go after the Nazis, but they're not around."