By Terri L. Heard

This healthy show doesn't need a blood transfusion, so why the devil is Buffy creator Joss Whedon injecting it with a major new cast member?

Tonight's season premiere introduces (very briefly and at the end) the Slayer's 14-year-old younger sister Dawn, a 12-18 demo-friendly sibling who, on the surface, appears to be Whedon's attempt to pull in a younger audience. Fans may already be scratching their heads wondering how the heck they overlooked the kid through the series's last four seasons. Ah, but Dawn was mentioned, supervising producer David Fury has said. Dawn was apparently the "Little Miss Muffett" Faith referred to during Buffy's dream in season three's two-part graduation episode.

If that still leaves you saying "huh?" don't despair. The answers are coming.

But not tonight in the fifth-season opener, when Dracula (Rudolf Martin) casts his dark shadow over Sunnydale. Typically, the count puts the moves on an older and wiser Slayer (Sarah Michelle Gellar), who's already been down this road before with her gloomy ex, Angel. But what Dracula's got that Angel doesn't are his legendary powers of seduction and his inside knowledge about the Slayer's gifts. His tantalizing hints spark a change in Buffy with repercussions for the entire season.

Another shadow lingers over the series.

Because few series make it to a fifth year much less go beyond it, this could be a critical season for Buffy. The cast is (relatively speaking) getting older. And with Buffy's transition to college and the tricky love affair between Willow (Alyson Hannigan) and Tara (Amber Benson), the show has steadily taken on a more grown-up tone. That may not bode well for it on the teen-oriented WB where, besides Angel, the network's more adult-oriented dramas (Felicity, Jack & Jill) haven't been great ratings successes.

Also, the show has weathered Angel's spinoff, Sunnydale High's destruction, and Faith's hijacking of Buffy's body and her boyfriend Riley (Marc Blucas, who returns sans the Initiative). Near the end of last season, the "Scooby Gang" saved the world for the umpteenth time by defeating the Initiative's fugitive manmade monster, Adam. There are just so many Armageddons and possessions before the plots themselves risk getting old.

But so far Whedon and crew seem to have dodged that bullet — at least regarding the storylines — by continually coming up with quirky ideas executed in a tight and inventive style. And every so often the series has transcended itself as it did last season with the classic episode "Hush." Buffy and her cohorts found themselves mute and forced to fight the malevolent Gentlemen without being able to utter a sound.

That episode, penned by Whedon, earned the series its first Emmy nomination for writing. It didn't win. The show plays like a full-fledged adult drama. The Emmy voters apparently see it as a kid's weekly horror-fest and the arrival of Dawn won't change that perception.

Still, it may be premature to judge how Dawn will or won't influence the tone and dynamics of the show — and its future. Although tonight's episode features the Slayer's showdown with Transylvania's celebrated bloodsucker, more Dawn is on tap in next week's episode, "The Real Me," much of which is told from her point of view. A few weeks after that, in "No Place Like Home," we'll get the full scoop about her. That story introduces a terrifyingly powerful new enemy and kicks off a potentially fascinating — and touching — story arc that carves out new psychological terrain for Buffy.

With Whedon at the helm, it's sure to be a deliciously ghoulish funhouse ride.

Maybe this time, when it's over, the Emmy voters will stake Whedon to a long-overdue souvenir statuette.