"We fight the demons," says Alyson Hannigan about her character, Willow Rosenberg, who is ever loyal to the bold and beautiful Buffy (Sarah Michelle Gellar) on Buffy the Vampire Slayer. "And, you know, we also hang out at the mall."

Soon, a force more insidious than vampires will test the strength of their relationship--a third friend is about to enter the mix. For the odd girl out, that's worse than a stake through the heart. "I was in that situation in high school," says the Atlanta-bred Hannigan, 24 (her real estate agent mom, Emily, still lives there; her truck-driver dad, Al, lives in Missouri). "I had two best friends, and they didn't get along. But it all worked out. You realize that you can have more than just one friend."

After her dogs and cats, Hannigan names boyfriend Levon Webb, a writer and former set dresser for the show, as her best pal now. But if her recent social schedule is any indication, her Buffy buddies have special status: a rock concert with Seth Green (who plays Oz); a Mexican dinner with Nicholas Brendon (who plays Xander Harris); a trip to the manicurist with kindred spirit Gellar.

It's little wonder she is so fond of the show. "I wouldn't trade this part (on Buffy) for anything," says Hannigan, whose credits include the films "My Stepmother is an Alien," "Dead Man on Campus" and this April's teen-sex comedy "American Pie." "I completely love Willow the most." So, it seems, does Buffy. But will their relationship endure? Hannigan isn't telling. "Remember last year when Angel became evil? You know how that basically changed the whole show? Well there's another thing like that coming up, but I can't give it away because [the producers] will kill me off." And on this series, it's best to take their word on that.