The Dollanganger siblings are back. “If There Be Thorns,” the latest installment in Lifetime’s adaptation of V.C. Andrews “Flowers in the Attic” series, premieres tonight – reuniting viewers with Cathy and Christopher. After fighting temptation in the first and second movie, the brother and sister finally caved into “sin” to live a life together as husband and wife.

Australian actress Rachael Carpani is the latest star to play Cathy, taking over from Kiernan Shipka in “Flowers in the Attic” and Rose McIver in “Petals on the Wind.” Cathy is older now in “If There Be Thorns,” and trying to raise her two sons from previous relationships – Bart (Mason Cook) and Jory (Jedidiah Goodacre). However her past threatens to unravel her happy family and expose her twisted secret to the world.

A definite dark and haunting movie, Carpani revealed to the International Business Times that she felt some responsibility with taking on the role – “not just have Cathy be a weeping mess through the whole thing.” “If There Be Thorns” viewers will understand what the actress is talking about when the third film airs. Cathy has been on an emotional rollercoaster since getting locked in an attic for years by her mother Corrine (Heather Graham) in the first flick. Despite a few moments of happiness, things have not gotten easier as the years passed.

“I just wanted to take every opportunity where her and Chris [Jason Lewis] had created this dream like world – this fake world, really, where they’re living as husband and wife and raising two children,” the 34-year-old actress continued. “[It’s] almost like they’ve become dolls themselves.”

Carpani added it was important for her and co-star Jason Lewis to “take advantage” of the few moments of contentment and happiness with Cathy and Christopher. “Because it doesn’t last long with those two,” she laughed.

Although Rachael Carpani was taking over a character that was played by two actresses previously, she surprisingly didn’t look to Shipka or McIver’s performances to craft an older version of Cathy. Instead, she explained that she looked at Heather Graham’s portrayal of Dollanganger matriarch Corrine.

“I looked a lot at Heather’s performance in ‘Flowers in the Attic’ in terms of that touching way she plays happy family with her husband in the beginning,” she revealed, referring to the first five to 10 minutes of the movie. “That almost doe like way … I figured I was playing [Corrine] around the same age.”

And while Shipka and McIver were both important in exposing Cathy’s hardships and bringing the character to life, Carpani felt like she wouldn’t be adding anything to the role if she tried to imitate them.

“I concentrated more on the energy of both the actresses in the films,” she added. “Otherwise you just end up imitating another person’s performance, and it’s less about them. I think for the audience it’s more about watching and just sort of recognizing traits about Cathy. The point is to see her journey through different stages of life. So you don’t want to see her exactly the same.”

For Carpani, Kiernan Shipka’s portrayal of Cathy in “Flowers in the Attic” really “grounded” the movie. McIver, on the other hand, brought a “delicate naivety” to the role.

“She was in her late teens, early 20’s and just going out into the world on her own,” the actress continued. “And the world bruised her up quite badly and literally – [Shipka and McIver] are two different actresses and we weren’t all cast because we look [the part]. People age and change over time.”

Lifetime viewers will see what Rachael Carpani is talking about when “If There Be Thorns” premieres on Sunday, April 5, at 8 p.m. EDT.