Kirsten Vangsness, Shemar Moore

Criminal Minds' quirky lab tech Penelope Garcia is about to show her BAU colleagues — and viewers — a side of her they've never seen.

On Wednesday's episode, the show will reveal that Garcia (Kirsten Vangness) spends her time outside the lab acting in a theater troupe. When Hotch (Thomas Gibson) finds out, Garcia begs him to keep it a secret from the rest of the group.

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But the truth comes out when a woman dressed like a 1950s starlet is found murdered in an alley. In their investigation, the team discovers that her murderer, played by Prison Break's Robert Knepper, has cut off her lips in a deranged homage to his former movie star mother (Sally Kirkland). When a second victim goes missing, the team needs to draw the killer out, so Hotch calls on Garcia to use her acting skills.

"They call upon her in a different way," Vangsness tells TVGuide.com. "Usually she uses her brain smarts and her emotional intelligence, but she's never been asked to step up. She's probably better than all of them at trying to be somebody else."

But Garcia isn't very happy that Hotch lets the cat out of the bag. "I think it hurts her feelings," Vangsness says. "It's her private stuff, but at the end of the day ... it also provided her this expansion that made her feel really good. He believes in her more than she believes in herself about those sorts of things."

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So will Garcia continue to move out of the lab more? "I think that will probably come up again, now they know she has those powers of transformation," Vangsness says. "But there are certain things about people that don't fundamentally change, so she's not going to wake up one day and all of a sudden be OK will all the blood and gore. Garcia's never going to be running around with a gun in her hand."

Meanwhile, Knepper — who, in addition to playing convict T-Bag for four years on Prison Break, has recently played twitchy villains on Heroes and Chase — thought twice before accepting the role.

"I don't know if it's a blessing or a curse that people just seem to think, 'Oh, Knepper? He's the go-to guy for a really complex character that happens to be intense or crazy," the actor says with a laugh. "I hope it's because they know I am going to make him a real person and not a one-dimensional kind of guy. It was one of those parts where I didn't want to do it because it was a demented character, but I couldn't not do it because it was such a great character."

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While the episode's mother-son dynamic and focus on old-school starlets brings to mind Alfred Hitchcock's classic, Psycho, Knepper says his character is no Norman Bates. "Sally's character was a beautiful starlet, and then she got knocked up and that was it," Knepper says. "She loves her son because he's her only child, and yet he f---ed up her career. But he's not browbeaten like Anthony Perkins' character. We made him kind of tougher. He's a guy who will stand up and say, 'Don't mess with me or I'm going to cut your lips off!'"

The role also resonated with Knepper, whose own mother died eight years ago. "It was pretty heart-wrenching," he says. "Even though I am dealing with cutting lips off of pretty young girls, there was a real emotional reason for doing it. Chalk it up to realizing that you just can't bring your mother back. You save a lot of bucks in therapy when you play a part like this."

Criminal Minds airs Wednesday at 9/8c on CBS.