Sarah Michelle Gellar overcomes death -- and a network change -- in a funny, scary two-hour season premiere on UPN.

EW GRADE: A

You knew she'd be back, didn't you?

I'm not just talking about the return of "Buffy the Vampire Slayer" the show. I mean Buffy Summers (Sarah Michelle Gellar), the vampire slayer who sacrificed herself to save her sister, Dawn (Michelle Trachtenberg), at the end of last season and the end of this series' stay at The WB. In making a business move over to UPN, this remarkable creation by writer-producer-director Joss Whedon -- a work of resonant fantasy unequaled in television -- has come up with a ripsnorting two-hour season premiere.

I'm not going to spoil the plot mechanism that returns Buffy to action (it's not giving anything away to repeat: You knew she'd be back, right?). But other mechanisms deserve their due, one of them being Gellar's witty performance as the "Buffybot" -- the robot Buffy who was used as comic relief in a few episodes last season. In the first hour of the "Buffy" premiere, written with slicing wit by executive producer Marti Noxon, the series that had turned morosely bleak regains its stubborn humor, as Buffy's pals -- Willow (Alyson Hannigan), Xander (Nicholas Brendon), Spike (James Marsters), Giles (Anthony Stewart Head), Tara (Amber Benson), and Anya (Emma Caulfield) -- crank up the Buffybot as a temporary-replacement slayer until they can figure out how to raise Buffy from the dead. "We need the world and the underworld to think that Buffy is alive," says Giles -- the underworld being that universe of vicious creatures who forever threaten the heroes' small town of Sunnydale, site of the demon-spawning Hellmouth. (Just explaining the "Buffy" mythology after five seasons is both tricky and a testament to the richness of the world Whedon and company have created.)

Anyway, Gellar-as-Buffybot is chipper, literal-minded, and, literally, mindless: Her whirring motor "brain" works overtime during what Willow calls the bot's "most dangerous challenge ever" -- which proves to be passing herself off as human at the local school's Parent-Teacher Day. Noxon's script glides smoothly from this humor to some hard-boiled action scenes. Hannigan is terrifically commanding in the opening sequence as a witch-power-enhanced Willow who beams out telepathic orders to her friends -- she'll remind comic-book fans (of whom Whedon is one, big time) of the telepath Jean Grey in "X-Men."

The show's first hour -- again, I'm not giving anything away that hasn't been previously announced -- paves the way for Giles' exit from the series; Buffy's Watcher (her trainer, counselor, and confidant) is returning to his native England, where in real life Head will head up his own new Whedon-created series for Brit telly. As usual in "Buffy," tender moments such as Giles' leave-taking are handled with a sorrowful delicacy as touching as any show on the small screen. "Buffy"'s second hour revs up the plot. This section is written by coexecutive producer David Fury, and its more serious, scary-movie elements pay homage to a couple of films by director Brian De Palma, specifically "Carrie" and (lesser known but befitting the teleplay author's name) "The Fury." I'm leery of divulging specific moments, but the closing hour features demon bikers, a few brief scenes that confirm the producers aren't going to shy away from the ongoing romance between Willow and Tara, plus Xander's first use of the musical-comedy theater as metaphor ("We got trouble, right here in Hellmouth city," he says, a Music Man of mayhem). This is perhaps a winking prelude to the musical episode Whedon has vowed to do later this season; reserve your seats now.

The final hour rewards fans with a renewal of dramatic energy for the series and, at the same time, enables new viewers to catch up on what amounts to a fresh start for the show. Taken together, the two hours unfold like a legend being told for the first time. Who'd have thought that lowly UPN, so blessed to be the new home of "Buffy," can now hold its head high and boast that it can go toe-to-toe with HBO? It's got a series with as much emotional punch as "The Sopranos" (yeah, go ahead, the snobs among you, sneer) and one whose scarifying coffin scene alone gives new menace to the phrase "Six Feet Under."