TORONTO -- Sure, she's only 15. But she's got a secret, and Michelle Trachtenberg is one tough nut to crack.

"Tell me Buffy's not really dead!" I said to her yesterday by way of jokey introduction, pretending to sob.

The girl who plays Dawn, Buffy The Vampire Slayer's TV sister, laughs and turns to the Fox executive who sits in on all her interviews.

"You notice how he did that?" Trachtenberg said. "It's like 'Tell me Buffy's not really dead!' and then he's like... (she puts her hand to her ear E.F. Hutton-style).

"They've tried every trick in the book on her today, Jim," the bemused woman from Fox said.

The last that fans saw of their heroine, Buffy, she'd given her life to defeat the vengeful spoiled-brat of a god named Glory, repaired a rift between earth and the dimension of demons, and saved the life of her sister (who didn't even exist until this season, but was magically brought into existence by monks trying to hide the cosmic "Key" from Glory ... but we digress).

But the smart money says Buffy comes back from the dead, because (a) they've done it before, and (b) the show is called Buffy The Vampire Slayer.

Of course, there's buzz that Trachtenberg might be groomed to be a Slayer herself (Vampire Slayer: A New Dawn!). But, again, it's a secret -- one to which Trachtenberg is privy.

"It's pretty confidential," she said. "When I found out, we were all kind of, y'know, on our way out the door, the season was over, Sarah (Michelle Gellar, a.k.a. Buffy) was off to Australia. We found out, and that's where we left it.

"Dawn is still there, that's all I can tell you,' she said.

Flown up yesterday by YTV (which airs Buffy on Saturdays), Trachtenberg had a busy homecoming in Toronto -- where she has shot Harriett The Spy and two TV movies. She had interviews all day and an English Lit final, written in absentia from the L.A.-area private school she attends.

"It's pretty tough," she said of the exam. "I can't afford to write it unprepared." Does she ever fail? "Oh no! I'm way too big a perfectionist."

Playing Buffy's sister comes fairly naturally to Trachtenberg, since her relationship with Gellar goes back seven years to when both were in All My Children ("I was, like, eight ... eight-ish," said Trachtenberg, who played an autistic child -- an ironic casting, since she is a self-admitted chatterbox). Both have a rapidfire speaking style -- "You ask us one question, we'll answer eight," she said.

It was good to have a friend on-set, Trachtenberg said, since Dawn was not introduced gently. She was called upon to react with the death of hers and Buffy's mom Joyce, in an episode being touted for an Emmy. Soon, she was at the centre of an imperiled universe.

"That (Mom's death) episode was very difficult for me, because I have such a close relationship with my mom. I had to work hard not to apply that storyline to my own life, which is what I usually do. It's difficult for me to talk about even now.

"It was all a little nerve-racking," she says of her debut season. "They'd all been together so long and were a well-oiled mix. I was worried I'd be water in the oil. But I blended right in there and became oil myself. It helped that I was a huge fan of the show."

After Gellar, she gets along best with James Marsters, who plays the used-to-be-evil vampire Spike.

"I'm very lucky to work with a cast of good people. James is just a lot of fun. He tries to teach me to play guitar, which is a little pointless 'cause I refuse to cut my nails."

Other high school kids go to school and talk about last night's Buffy. What does Trachtenberg do?

"Now and again, some ninth-grader will come up and, like, say 'Ohmygawd!' My friends and I don't talk about the show very much.

"Y'know, we discuss what regular teenage girls discuss -- guys, the latest fashion trends, makeup and 'Ohmygawd, why did she cut her hair?' "