"I've done it," Joss Whedon (search) says gleefully. "I've made a movie where there's a discussion about the human condition during a hovercraft chase!"

That movie is "Serenity," out this weekend -- and it was a true labor of love for Whedon, a prolific screenwriter best known for his hit TV series "Buffy the Vampire Slayer."

After that show ended in 2003, Whedon went on to create a new series, "Firefly," which left the world of teen angst and vampires behind for a high-concept combo of space adventure and old-time Western.

Despite critical praise, the show had an insect-like life span. But much to his surprise, Whedon then got an opportunity to resurrect "Firefly" on the big screen.

"Serenity," Whedon's directorial debut, aims to introduce a wider audience to the "Firefly" universe: 500 years in the future, it's a place where spaceship pilots speak and dress like frontier settlers and curse in Chinese, the human race is scattered across countless Earth-like planets and prostitutes are revered like royalty.

The show's hero is the captain of the rickety spaceship Serenity, Malcolm Reynolds (Nathan Fillion) -- a character Whedon says owes a debt to the original space renegade, Han Solo.

"If he's not his father, then definitely a weird uncle," the director says with a laugh. "He's obviously an influence on the character. Mal's like a Han Solo who never met a Wookie or found the Force."

Though Mal and his crew (see sidebar) make a living pulling heists, they always end up on the good side, in spite of the captain's best efforts.

Caught between the two sinister forces in the "Firefly" universe -- the cold, omnipotent Alliance government and the cannibalistic space pirates known as Reavers -- Serenity is under fire for harboring a fugitive 17-year-old named River (Summer Glau), who's escaped from a government experiment.

Not so shockingly, the preternaturally smart River turns out to be a terrific fighter; if Mal's ancestor is Han Solo, then hers is undoubtedly Buffy Summers.

"This was supposed to be the point where I got over it," says Whedon of his obsession with superhero-like teen girls. "But I guess not."

With Whedon's trademark strong female characters, rapid-fire dialogue and intricate storylines, "Firefly" garnered a fiercely loyal following of fans who call themselves Browncoats (in homage to the show's Western attire) and they've been mobilizing to get the word out about the film.

But while their passion is strong, the Browncoats' numbers are small. The crucial question is: will the uninitiated go for it?

"I have no confidence of any kind," admits Whedon. "I'm not a marketing guy. I have no idea if people who don't know me will see this.

"But," he continues, "I believe firmly that if they do go, they'll have a good time."

The director says he's satisfied that the movie tells its own story, apart from the show.

"It's not the last episode of something else -- it exists in and of itself," he says. "I like to feel a sense of closure."

So, then, what would he say if there was demand for a sequel?

"Could I do more of these?" he says. "Hells, yeah!"