Lea Thompson was slowly scratching a big red bug bite on her thigh with her left hand in a backstage dressing room at Studio 54. Her other hand held a plastic cup of Diet Coke, from which she periodically drew long, mighty sips through a straw. In two hours, Ms. Thompson was due to take the stage in the revival of Kander and Ebb’s Cabaret as Sally Bowles, a hedonistic American cabaret singer in pre—World War II Berlin who escapes her troubles in booze, men and song. But as Ms. Thompson sat on a tiny couch wearing green short-shorts, a gray T-shirt and green nail polish, she reflected on a much earlier role: her turn as the younger version of Michael J. Fox’s mom in Back to the Future.

"That was a twisted part," Ms. Thompson, 39, said of her role in the 1985 film. "The depth of it: Oedipus and replacing your father and your mother being in love with you–those themes are really strange. I understood the character very well, the horny little 50’s girl I was playing. It was just like a cat. I had images in my mind. I was cat, you know."

Ms. Thompson purred.

"Cause I grew up with cats and when they were in heat, when I was growing up in Minnesota. You know, ‘Puuuurrrrr. Purrr. Purrrr.’ That’s basically the image I used."

Remember, reader, Ms. Thompson’s lethal mixture of girl-next-doorness and subterranean sexual energy that drove everyone wild, oh, those 15 years ago? There were other great parts, too. She was the girlfriend in All the Right Moves, an early Tom Cruise vehicle. She was the high school princess in John Hughes’ Some Kind of Wonderful and C. Thomas Howell’s girlfriend in Red Dawn, one of the top films ever made about Midwestern high school students forming a militia to defend the United States from an invading Soviet army. Ms. Thompson even managed to spice up Space Camp. Whatever it was, she had it, and we just knew Ms. Thompson was going to entertain us for years to come.

But then something horrible happened. Caroline in the City happened. It was one of those pleasantly bland NBC sitcoms that’s bad, but somehow not bad enough to get booted off the air. We waited patiently for four years while Caroline went through its tortured cycle, waiting for the real Lea Thompson to return. Then Ms. Thompson began appearing in Chevrolet truck commercials, speaking the memorable line, "It’s the Chevy make-your-money-count year-end event: 2.9 percent A.P.R. financing on Chevy Malibu."

"I don’t get many offers. I basically do what people give me," Ms. Thompson said. "I auditioned for all those weird movies and no one would give them to me. They just gave me the normal stuff because I looked normal. It’s always about the new girl. It’s always about the new girl. They’re cheaper. Once you get your price up–and the parts aren’t usually that difficult–so they’re like, ‘Get the new girl, she’s cheaper.’ I used to be jealous and now I’m like, ‘Aw, you got a couple of more years.’ So you’ve got to do TV. You’ve got to do theater, you do TV movies, you do commercials."

And what about those Chevy commercials?

"It’s not like I was sitting at home saying that I have this great truck," she said. "I like the fact that I went up there and said, ‘Hey, buy a Chevy.’ There’s something really honest about it. I’m just selling. I didn’t have to lie. I didn’t have to say I only drive Chevy trucks. I didn’t even have to say ‘Hi, I’m Lea Thompson.’ I don’t know. I have had the weirdest career. I don’t even try and guess it anymore."

Ms. Thompson was having a moment.

"I just do what they tell me to do. Whatever comes up. You have to. I have never been one to sculpt my career. I should have, obviously. But I never sculpted it."

Now perhaps Ms. Thompson has found the perfect role in Sally Bowles.

"She’s not that bad of a girl," Ms. Thompson said of her character in Cabaret. "She’s all about love and I have a lot of love in my heart. I have a big family. I have a big heart and I relate to her. She just gets a little misguided, that’s all. She’s in a bad place at a bad time. You’re supposed to be good, stay home, don’t get out of line and say ‘yes, sir’ to every man that tells you to do something, and she’s not like that. Any strong sexy woman always has a hard time in this world."

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This is a frame from Hoprdox's Lea Thompson Fanpage