We've got a few questions about tonight's episode of "The X-Files" as the show begins its eighth (and possibly final) season on Fox: First, how are they going to replace one of the show's two seemingly irreplaceable stars, David Duchovny, who signed a one-year contract that will require him to appear in only a few episodes this season? How do they intend to keep our interest after a season in which many of the show's long-running story lines were finally sewn up? Are there still more gimmick episodes in our future, like the ones last season that inserted Scully (Gillian Anderson) and Mulder (Duchovny) into a taping of "Cops" and had Garry Shandling and Tea Leoni play them in a movie? And what's the deal with that drill going into Duchovny's mouth? If nothing else, we'll tune in just to find out The Truth behind that two-second clip, played over and over in commercials that aired during the World Series, showing some kind of involuntary oral surgery being performed on Mulder. I know this will shock you, but few if any answers to these questions will be furnished tonight when "The X-Files" returns at 8 on Channel 4. Nor will we know much more when the two-part season premiere concludes next Sunday. So it appears that TV's longest-running and weirdest manhunt - or alien-hunt, whatever - will continue for another full season. But the vanishing of Mulder raises the stakes in the paranormal pursuit. Did it ever seem like no one else at the FBI cared what happened to the X-Files? That has changed in a hurry now that one of the agency's own is missing. Which brings us to what was likely the year's most suspenseful "X-Files" moment. Last spring, it seemed the Fox network was teetering on whether Duchovny would agree to play Mulder for at least another season. Eventually he did, but on such a restricted schedule that a new partner for Scully was needed. (Look for Duchovny in about half of this season's episodes, many of those minor appearances.) Enter Robert Patrick, perhaps best known as the futuristic robot T-1000 in "Terminator 2." He plays Doggett, a streetwise former cop brought in by FBI higher-ups because Scully and her boss, Skinner (Mitch Pileggi), were both witnesses to the alien kidnapping of Mulder in last season's finale. "Witnesses," as we soon learn from the chisel-faced Doggett, is bureauspeak for "suspects." Though a cloud of suspicion hangs over them, Scully and Skinner can't do much to clear their names. As usual, the aliens they are pursuing have made off with nearly all physical evidence of their chicanery. No one has a clue where Mulder went when he was sucked into the aliens' force field. Scully has premonitions, however, that it can't be a very nice place. (Maybe she was watching the World Series, too.) On top of which, Scully is pregnant. By whom - or what - we're not told. Mulder's disappearance, and the circumstances under which it happened, have altered the familiar chemistry of "The X-Files." Scully, once the scientific skeptic, has become the true believer. Nor can Skinner deny he saw what he saw, either. So now it's the new guy's turn to be the designated doubter. "You know, Agent Scully," growls Doggett in next week's episode, "you're starting to remind me of Agent Mulder yourself." In other words, the more things change, the more they adhere to "X-Files" creator Chris Carter's time-tested television formula. But longtime fans of the show will be forgiven for wondering if this isn't simply the re-arranging of deck chairs aboard a sinking ship. Anderson, who has signed through next season, is itching to get out of her contract. She's a fine actress, as you may have seen in the 1998 film "Playing by Heart," and as recently as last month she told a British newspaper she'd like to try other things besides TV. Duchovny, it would seem, has signed his last contract to play Mulder. And, of course, Nielsen will be the judge of whether Patrick returns for another season. So once again, the climactic scenes in one of TV's most influential drama series will likely be played out next spring not on camera but in closed-door meetings between Carter, the Fox network and the show's reluctant stars, our Bogey and Bacall for a cerebral, agnostic era. To reach Aaron Barnhart, phone (816) 234-4790 or visit the TV Barn Web site at www.tvbarn.com @ART CAPTION:"T2" veteran Robert Patrick (left) joins the cast of "The X-Files" as Gillian Anderson searches for David Duchovny, above, who was last seen being abducted by aliens. @ART CREDIT:Photos courtesy of Fox @ART CAPTION:Robert Patrick (left) joins Gillian Anderson and Mitch Pileggi this season on "The X-Files." @ART:Photos (4, color) >>>