Is there anyone out there?

The second X-Files movie is going back to basics in a bid to lure back old fans – and win itself some new ones, writes MARK HARRIS

CHRIS CARTER, THE CREATOR OF The X-Files, has a message for anyone who, sometime during the show's nine-season run, threw up their hands trying to figure out exactly what was going on with the extra-terrestrial abductions, the black-oil aliens, the metal sinus implants, the Syndicate, the Cigarette-Smoking Man, Mulder's sister, Scully's baby, Mulder's father, Scully's cancer, the colonists, the Lone Gunmen, Deep Throat and all the rest of the show's staggeringly complex and often murky mythology: You can come back now.

Of course, there are those who never left, who have kept The X-Files alive since the series finale five years ago via online episode guides, message boards and no small amount of erotic fan fiction.

And Carter will be delighted if they show up to see The X-Files: I Want to Believe, his big-screen attempt to see whether there's still an audience out there for the paranormal probings of the FBI agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson).

But Carter, and Twentieth Century Fox, are especially interested in casual viewers who may stay away out of fear they have 202 hours of homework to do first.

There's no need. I Want to Believe is, in X-Files argot, a stand-alone: a self-contained story reminiscent of several beloved early episodes in which Mulder and Scully were dispatched to a remote (but always vaguely Canadian-looking) location to confront an undefined, menacing presence. Carter promises not only scares but a beginning, middle and end, none of them overly entangled in back story. Everyone is invited to jump aboard.

At least that's the idea. The first X-Files movie, released ten summers ago, was so elaborately knitted into the show's storylines that it had to open precisely between seasons five and six. The film grossed $84 million, impressing many who doubted that people would pay for a super-sized episode of a series they were used to seeing for free.

A decade later, in the wake of the big-screen successes of The Simpsons and Sex and the City, the TV-to-movie genre has considerably more credibility. But the success of I Want to Believe is far from assured.

Five years out of sight is a long time even for a popular franchise, and when Fox gave the go-ahead to Carter and his co-writer and co-producer, Frank Spotnitz, the green light came with a low budget of $30 million (£15 million), a strong expression of preference for a user-friendly PG13 rating and a now-or-never timetable predicated on finishing the script before the writers' strike last winter.

The mere existence of a new X-Files movie represents something of a triumph of patience and persistence. "These things take a while," says Tom Rothman, the co-chairman of Fox Filmed Entertainment. "The show is very personal to the creative team, and the stars, literally and figuratively, had to line up."

That was by no means a certainty when the series left the air. Duchovny had quit a year earlier, eager for more family time and other work, and perhaps weary of the show's hothouse atmosphere. "There were relationship repairs to be made, certainly, between David and me," Carter says, of the later years of the run.

Anderson stayed until the end, but by then, she says: "I wasn't even sure when I would be interested in being on a film set again, period." She added: "It can get so all- consuming and incestuous."

Duchovny, 47, went on to make several movies and now stars in the Showtime comedy series Californication. Anderson, 39, moved to London, where she established herself on stage, in television (Bleak House) and in film (The Last King of Scotland). Back in the US, she is now the host of Masterpiece Classic on PBS.

Carter and Spotnitz already had an idea for a new X-Files movie when the series ended, but it was shelved when an argument with Fox over syndication profits led Carter to file a lawsuit in 2006. "To resolve it took me longer than I had anticipated," he says of the protracted dispute, which was amicably settled. "But the day my representatives were calling me saying it's over, Fox was on the other line saying, 'Do you want to make this movie?' "

The long delay necessitated a fresh approach, not to the plot but to the characters. "We had tried very hard to think of something we had not done before," Spotnitz says, "and we came up with an X-File that was very creepy and disturbing. But that was in 2003. By 2007 we realised that the Mulder-and-Scully aspect of the story had to be different because of the passage of time. "The movie, which acknowledges that several years have elapsed, is more about them and their relationship."

Both actors were enthusiastic about the prospect of an instalment that did not rely on the series' labyrinthine plotlines. "I never was able to follow the story," Anderson says, laughing. "Some people who spent a lot of time hashing it out might have been able to make sense out of everything, but I got lost."

Duchovny says he welcomes the screenplay as a chance for "the characters to have a clean slate on which to create themselves again".

"And the mythology still exists," he adds. "Even if we don't bring it to bear in a specific movie, viewers who were into all that will understand some moments and reactions a little better."

I Want to Believe was shot in Vancouver, the series' home for its first five years, and a place where Carter could stretch his budget, given a weak US dollar. The return to Canada was not just a homecoming, he says, but a plot necessity. The story, which includes roles for Amanda Peet and the rapper and actor Xzibit as FBI agents – and Billy Connolly as a spooky maybe-psychic – required a location with a metropolitan area, a nearby forest and snow.

Under Carter's direction, the shoot may have felt like a family reunion, but that's not to say everyone was instantly at home. "I walked in thinking, it's going to be like riding a bicycle," Anderson recalls. "It wasn't. It was like riding a unicycle," and she modifies unicycle. "I'd been trying so hard to stretch myself in other roles, and to catch myself when I did anything that remotely resembles Scully, that when I was put back in the ring with her, my brain started misfiring."

The challenges for Duchovny were more physical. "It's been a while since I worked on those night shoots," he says. "I'd forgotten how bodily taxing it can be, standing in the cold or trying to chase somebody down at four in the morning."

Both actors say they're up for more sequels if the demand is there, however – and so are Carter and Spotnitz.

In April, when the two men unveiled anX-Files movie trailer at a Q&A session in New York, a crowd of more than 2,000 greeted them as though they were rock stars. A fair share of those in attendance were old enough to be the parents of the teenagers milling around the graphic novel and action figure displays, and many had clearly been keeping the faith.

Carter and Spotnitz, both practised in the art of revealing little, fielded questions gamely if obliquely, including a number of inquiries about whether Scully and Mulder might ever become romantically involved. It's the question that will not die and it perplexes Carter, who says: "I never wanted to domesticate the show, to make it simply about Mulder and Scully rather than about the quest they share."

Duchovny, told of the questions, says: "I'm not surprised people are still curious. It's really the kind of weird marriage they have, that perfect and imperfect relationship, that gives life to the whole enterprise."

Anderson used to find the whole idea ridiculous. "There was always part of me that thought, 'What's so special about these two, and will everybody not shut up about it?' " she recalls. "And then, while we were doing this movie, somebody sent me a link to a YouTube montage that a fan had put together of Mulder and Scully. Clips of our growing intimacy through the series. One, it was really moving, and two, I couldn't believe how many times we held hands and actually kissed. And I was left with my very first understanding of what the fans were on about. I finally kind of got it.

"Because the clips show that there may be room for more – I'm putting my foot in my mouth," she says, changing the subject. "But if we had given them what they said they wanted years ago, it would have ruined the series."

• The X-Files: I Want to Believe is released on 1 August.