On Thursday, Oct. 4, during the third-season premiere of The CW's horror drama "Supernatural," fans got their first look at knife-wielding Ruby (Katie Cassidy), the new rival in the demon-hunting biz to the Winchester brothers, Sam (Jared Padalecki) and Dean (Jensen Ackles).

It wasn't a friendly meeting, with Ruby taking down a few demons with her magic blade and then informing Sam that, "I'm the girl who just saved your ass."

The irony in this statement will become more evident in future scenes, as the 5'7" Cassidy squares off with the 6'4" Padalecki.

"Most of my scenes are with Jared," says the blond Cassidy (daughter of '70s pop idol David Cassidy) over lunch in Santa Monica, Calif. "I'm pretty close to him. I'll be like this."

She cranes her neck back to look upward.

"I'm supposed to be very intimidating and badass," she continues, "this badass chick, and when I walk up to him, I feel like a shrimp. But I'm five-seven, and they give me huge heels. I'm in four-inch, three-inch heels."

And yes, she'll be running and fighting in them.

"I've been kickboxing for about six weeks now," Cassidy says.

She sticks out her hand and shows a good-sized scrape on one knuckle.

"This is actually my first boxing injury," she says. "It's healed a lot. It's kind of exciting. I'm eventually going to be kickboxing in heels."

Remember that old line about Ginger Rogers doing everything Fred Astaire did, but backwards and in heels? Such is the fate of the female action hero, even when fighting is not involved.

"It's funny," Cassidy says. "I had a scene, like, a week ago or two weeks ago, where we were by the water. I was in these super-high heels, and they're spiky heels, not chunky or anything. We're on sand, and I'm walking like this … ."

She mimes losing her balance and wobbling.

"I'm like, 'Really, can anybody see my feet in this shot? I look like I can't walk.' So they ended up working it out so I could be in regular shoes."

Cassidy's also a bit concerned about that damp, long winter in Vancouver, Canada, where the show shoots.

"I'm a little skeptical," she says, "because a lot of our scenes are night and outside. I have long sleeves and jeans on all the time, so there's no way you can layer anything. But it's going to be fun. I'm excited."

Ruby is one of two female characters introduced in "Supernatural" this year, along with mercenary Bela, played by Lauren Cohan. Fans who feel very protective of their boys apparently aren't too happy about the new women in their lives and the prospect of romance.

But fear not, says "Supernatural" executive producer Eric Kripke, who reveals, "Honestly, I have episodes broken through 14 at this point, and there isn't so much as a friendly hug between them. We'd rather keep tension in the air. The girls are actually pretty antagonistic to the boys.

"They're not really introduced as allies. They have their own motives, and they actually provide a lot more obstacles to the boys than they do assistance.

"So the boys spend a lot more time discussing how they want to kill then than how they want to kiss them."

Down the line, though, things could change.

Kripke says, "If the audience screams out for it after we've tortured them for years, then yeah, maybe we'll do it. But we thought we had a much better chance of successfully introducing these characters if they were just introduced as characters in their own right, with their own interests and their own motives, and not introduce them as accessories to the boys."

"I know the fans are die-hard," Cassidy says, "but we're not there to be love interests. We're there to be kick-ass. A girl's gotta kick some butt from time to time."

But revenge is sweet. Grabbing the ketchup to put on her fries, Cassidy recalls shooting a diner scene with Padalecki, in which she had to pick up a squeeze bottle of ketchup.

Apparently the top was unscrewed, and ketchup spewed everywhere. In what Cassidy says is a "Supernatural" tradition at blooper moments, the cast and crew serenaded her with "Happy Birthday."

"I'm so embarrassed," Cassidy says. "I don't know if Jared was trying to pull this funny prank on me or if it was just an accident, but he was like, 'I didn't do it, I didn't do it.'

"I'm like, 'You liar. You're an actor.'"