Julia Stiles in a killer role

Julia Stiles has played a lot of roles, but vigilante wasn’t on the résumé.

Until Dexter.

As Season 5’s mystery woman Lumen, Stiles is bent on avenging a group of sadists responsible for the “Barrel Girl Murders.”

Lumen would have ended up in a barrel, too, had the show’s hero, Miami blood spatter expert-cum-serial killer Dexter Morgan, not saved her.

Throughout the season, the two grow so close that Dex was able to bring his new friend into his murderous fold, inviting her into his so-called kill room and showing her how it’s done.

The on-set experience was a little nerve-wracking.

“There’s something sacred and unique about the kill rooms,” says Stiles.

A variety of knives — real and fake — are used for the grisly scenes.

“For certain angles you have to use the real knife, which is very sharp,” explains Stiles, 29. “Not until the moment of impact do you switch it out. You have to be very careful.”

Plastic-wrapped “victims” wear a chest plate to protect vital organs in case a stunt goes awry, like, say a dangerous knife gets mistaken for a blunt, retractable one (that happened to Jimmy Smits during season 2, but the actor was unharmed).

“It gets a little complicated, and everyone’s a little nervous,” Stiles says of the crew for the show that was just picked up for a sixth season. “I just have to make sure I follow the instructions.”

Speaking of complicated, what’s up with the finale? Last we saw of Dexter, crooked cop Liddy (Peter Weller) was on our hero’s trail big time, and had surveillance video of him doing bad things.

“All I can say is that the last episode is action-packed and really surprising,” Stiles hints. “What happens is unlike anything that’s ever happened on the show.”


Dexter’s finale airs 10 p.m. Sunday on Showtime.