An admitted fan of Meyer's other supernatural saga, "Twilight," Ronan recalled being blown away by the story of Earthling Melanie and the alien named Wanda who inhabits her.
"I had heard that 'The Host' was being made into a film and read the script and thought the concept was so incredible, just the idea of aliens sort of inhabiting Earth to perfect it," Ronan said. "That this was their goal — not to destroy it or really take it over, but just to perfect things and get rid of any negative emotion — was really intriguing to me, so then I read the book as well, and that was fantastic. It's huge. It's a big book."
At 600-plus pages, Meyer spared little detail bringing her post-apocalyptic tale to life, and according to Ronan, writer/director Andrew Niccol did right by the source material in his adapted script.
"He's obviously a fantastic writer," Ronan enthused. "That's his strong point: to do mind-blowing concepts like that. He's very good at that sci-fi type of drama. We've all said that how he was able to condense 600-plus pages into a 120-page script is kind of amazing."
With an impressive script to work from, Ronan's main challenge was portraying two separate characters in a single body.
"I'm viewing Melanie as a completely different character to Wanda, because they are. They are two separate young women," Ronan explained. "One happens to be an alien, and they're very different from each other. Melanie is a very strong, tough cookie — she's had to be, really. She's had to be tough in order to survive and take care of her younger brother. They've been on the run together for a very long time, and that's all taken away from her. It's very tough on Melanie."
And despite the usual portrayal of aliens as unsympathetic interlopers, Ronan had to try hard not to sympathize with Wanda.
"Wanda, it's an interesting thing to try and get rid of any negative emotion, to not feel any anger, because there are some points in the film where you think poor Wanda is being punished for certain things and being put through an awful lot."