By the time Buffy the Vampire Slayer was released as a feature film in 1992 with Kristy Swanson and Luke Perry, the film had turned into a comedy, which wasn't what Whedon had intended.

The film performed poorly at the box office but had a strong afterlife in home video. So much so that when 20th Century Fox pitched a TV spin-off to WB, the network said yes.

Styled this time as a straight horror show with occasional moments of humor, Buffy has turned into a surprise hit in its first three weeks, garnering WB's best ratings ever on a Monday (9 p.m. on Channel 20 in Detroit).

Buffy hovers near the bottom of the Nielsen TV ratings with a 3.4 rating (one ratings point equals 970,000 TV households). But in a midseason of mostly disappointments, when NBC canceled Prince Street after two outings and ABC yanked Spy Game after three, Buffy is the only rookie to instantly pop.

"We're overwhelmed," says star Sarah Michelle Gellar, who plays Buffy. "It did better than we could have ever hoped."

Whedon credits the tune-in to a strong advertising campaign by WB, the success of the movie on video and the recognizable name of the show.

"The title is in your face," he says. "Which is why the movie did so well in video."

Buffy has been described by reviewers as Beverly Hills 90210 meets The Shining, and Whedon doesn't disagree.

Buffy is a typical beautiful California high school student who happens to have a talent for slaying vampires.

In the TV version, Buffy's slaying skills are expanded to monsters of all kinds. In upcoming episodes, she'll also deal with a huge praying mantis, an Internet demon and a ventriloquist's dummy that comes to life.

The show's exteriors are filmed at Torrance High School in Torrance, Calif., which also served as the setting for the kids of Fox's 90210 back when they were in high school.

After Buffy, Whedon, 32, did uncredited rewrites on Twister, Waterworld and Speed and co-wrote the hit Toy Story. Returning to the horror genre, he also wrote the script for the fourth Alien movie, Alien Resurrection, due in July.

He's planning stories for the second season of Buffy, even though WB officially hasn't renewed it.

"You have to assume it's going to happen," he says. "Otherwise, you'd be scrambling when the call came in."