If you don’t know her name already, actress Caitlin FitzGerald, who stars on one of television’s buzziest shows, needs to be on your radar. “When I tell people I’m on Masters of Sex, there’s an awkward moment where they’re trying to decide if I’m a porn star,” says FitzGerald of her role on Showtime’s hit series about 1950s groundbreaking sex researchers William Masters and Virginia Johnson (the second season premieres July 13).

Lounging on the roof deck of the Ace Hotel in downtown Los Angeles, Calif., the actress, 30, looks anything but X-rated in a fitted Elizabeth and James blazer, J. Crew boyfriend jeans and Vince ballet flats. Between sips of coffee, she entertains questions about her different roles, among them her début performance playing the rear end of Bessie the Cow in a community-theater production of Jack and the Beanstalk. She’s at peace with that choice: “As they say, ‘There are no small parts, only small actors.'”

As Libby Masters, a new mom and wife to Dr. Masters (Michael Sheen), FitzGerald has learned a lot about infants on set. “They bring in six babies for a scene, so if one cries, they swap it out with another,” she says. “The other day, a baby fell asleep in my arms, and something flipped inside me. The emotion was intense.” Right now she is content with her Norfolk terrier puppy, Charlie. “Since I’m bicoastal, it’s good that he’s small so he can travel with me.”

FitzGerald, who grew up in Maine, boasts an intriguing pedigree. Her aunt, Frances FitzGerald, wrote a Pulitzer Prize-winning book about Vietnam (Fire in the Lake); her late grandfather was a deputy director in the CIA during the politically turbulent 1960s. “There’s family lore around him,” she says, showing off his Omega Constellation watch on her wrist. “My aunt picked up the phone once, and it was JFK on the line.”

On the red carpet FitzGerald turns to designers such as Gary Graham, Katharine Polk at Houghton, and Emilia Wickstead. “I love classic pieces with a contemporary edge,” she says. “I never want to wear the safe choice—that’s no fun.” When it comes to her style on Masters of Sex, its a whole different story. Her character is clothed in historically accurate costumes (down to the undergarments) that represent her goal to be a model wife in a world and a society that expects her to have perfect manners, dress and social skills. As a result, her costumes are feminine, soft, pretty and accessible, but with just the right touch of melancholy.

Check out Caitlin FitzGerald’s favorite Masters of Sex costumes in our gallery, and see what she has to say about them all!

This story originally appeared in our July 2014 issue. For more features like this, subscribe to InStyle now.