BURBANK, Calif. -- As the scene unfolds on the set of "Without a Trace," agents Samantha Spade and Martin Fitzgerald are looking through the one-way mirror of an interrogation room. On the other side of the glass, their boss, Jack Malone, is grilling a suspect.

"My guess is he didn't do it," says Fitzgerald. Spade, on the other hand, can't decide.

Guessing is an art form on "Without a Trace." The CBS Thursday-night series probes the mindset and emotions of not just villains and victims, but also the team of New York-based FBI investigators trying to solve missing-person cases.

Along with the procedural details essential on crime shows, audiences are offered highly complex lead characters, whose lives are deeply affected by the work they do.

"It's a high-pressure job. You see a lot of not-pretty things, a lot of the ugliness of the world. I think every character has a different response to it," said Poppy Montgomery, who plays Spade, a young agent determined to "prove she's tough enough."

In the series' inaugural season last year, Spade was shot with her own gun and had to be rescued by Malone, a married man with whom she had had an affair -- a relationship revealed after the fact.

"I love the way it was done. It's kind of mysterious -- so unexpected," said Montgomery, who started out thinking there would probably be an eventual love connection between her character and Malone, only to learn it had already happened.

Montgomery said fans ask, "'What's happening with Jack and Sam?'" Yet she doesn't know what will transpire, beyond the fact that Malone, played by Anthony LaPaglia, is back with his wife, and that some sort of relationship seems to be building between Spade and Fitzgerald.

LaPaglia chuckles about fans' interest in "that stuff."

He feels "that's maybe because we underplay it so much. We really don't give them concrete answers. Everything is kind of insinuated. I like that. I prefer that -- you actually have the audience participate by wondering. You let them think."

The critically praised series averaged about 15.1 million viewers and ranked 17th during its first season, with a hefty assist from lead-in "CSI: Crime Scene Investigation," the season's top-rated prime-time drama. Both shows are executive-produced by Jerry Bruckheimer.

"Without a Trace" creator Hank Steinberg says the episodes that were most successful last year had "some emotional resonance for our main characters" and the writers are keeping that in mind in the new season.

But procedure still counts, too, and technical adviser Mark Llewelyn, a former FBI agent, is always around to advise the cast.

"If I feel there is a false moment I say, 'Is this authentic?"' said LaPaglia.

Hourlong shows often require a quick wrap-up, which sometimes worries him.

"Not that long ago when I got someone to confess inside of 30 seconds, I asked, 'How long would it really take?' and (Llewelyn) said, 'Even if you had a picture of him holding a gun, it would take an hour and a half!"' LaPaglia said with a laugh.