"There are some pretty monumental changes ahead for our intrepid sex researchers," Lizzy Caplan tells PEOPLE

By Patrick Gomez
July 12, 2015 03:50 PM
Liz Von Hoene/Showtime

Lizzy Caplan promises things are about to get “very public” for the secretive researchers at the center of Masters of Sex‘s third season.

“There are some pretty monumental changes ahead for our intrepid sex researchers,” the actress tells PEOPLE of the acclaimed Showtime drama’s central characters, Dr. William Masters (Michael Sheen) and Virginia Johnson (Caplan), whose work finally earns notice.

“Most notably, their research is published and is well received – and they become celebrities as a result,” Caplan says.

Their “relationship and work has been shrouded in secrecy,” she continues. “But now it’s all about to get very public for them.”

The evolution of the series is one of the things Caplan says has always drawn her to TV work.

“I’ve always loved getting to grow along with a character,” says the actress, who broke out as Janice Ian in 2002’s Mean Girls. “It’s probably my favorite part of working in television.”

That growth will be evident to viewers in some surprising ways this season, she says. Credit that to the scale of the story itself.

“Our show is based on real people, and the story we plan to tell is over 30 years long, so both Masters and Johnson will change a great deal,” Caplan says. “When we first met Bill, he was very uptight, cold even. Virginia was the opposite: warm and charismatic. Over the course of the entire series, [what] you’ll begin to notice is how each starts to take on the characteristics of the other.”

Season 3 of Masters of Sex premieres Sunday, July 12, at 10 p.m. on Showtime.