The series gets underway at 9pm tonight (Wednesday 14th February), and ahead of the debut, Tointon revealed to RadioTimes.com and other press that she "instantly got behind" Rachel when she was handed the first two scripts prior to her audition.
"She feels like a lot of the country at the moment," she explained. "She's really struggling, trying to make ends meet, and I was quickly flying the flag for her. And I was desperate to know what was in store later on."
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Tointon also described the character as a "go-getter" who is "trying her best", but added that "everything's up against her" and "she's not got much of a support system".
She continued: "I suppose I was just really excited as I'm coming into a bit of a new phase of my career, playing slightly older characters, and it's interesting to be leading a psychological thriller and looking into coercive relationships.
"And it keeps you guessing, it's a bit of a rollercoaster of emotions, for sure.
"And you really have to jump on board with Rachel. It's her story, and that was really exciting for me. So it was something to get my teeth into. I really loved it."
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Meanwhile, Tointon said she was "proud" to be leading the cast – which also includes Downton Abbey's Allen Leech and Hullraisers star Taj Atwal.
"Many jobs you have, you dip in and out," she said. "So, for me, it was exciting to really have a character to get on board with all the way through four episodes, and it be heavily a drama about this woman struggling.
"I'm a mother of two, my kids are five and three. And becoming a mother, it gives you a new perspective on everything. And that's been helpful.
"But I liked Rachel because she's just a nice, young woman that you hope for the best for. But everything's up against her.
"So, you're just hoping that things come good one day, and she can keep trying. And this is a moment in her life where you think, 'Oh, my God, all her prayers are answered,' but everything's a little bit more serious than it seems."
Too Good to Be True airs on Channel 5 on Wednesday 14th February at 9pm. Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on.
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