They Grant and Parker play a married couple once wildly and romantically in love -- until Grant's character's cheats.
"Well, yes. Not to put too fine a point on it, I do. Once. And I regret it instantly and I don't enjoy it and I tell her instantly. But she throws me out. And this film really begins with me three months later, still desperately trying to get her back," Grant told Early Show co-anchor Harry Smith.
While trying to get back in her good graces, Grant and Parker witness a murder and have to be placed in the witness protection program. The two city folk are then sent off to a spot in rural Wyoming that Grant calls "the tiniest little cowboy town."
"Did you want to become a cowboy?" Smith asked.
"Yes, I felt a call of the wild. I like all that stuff. I had to have a cowboy outfit growing up as a little boy in West London - there's something about it," he said.
Grant said he thought he would look sexy in the cowboy outfit, but that wasn't the case.
"I've seen the film and I look ridiculous. I look like some old lesbian," Grant joked.
Grant has been out of the romantic comedy circuit for two years now. And although he said it's because he's a little "lazy," what it really comes down to is that he's "very choosy."
"I drive agents mad. I won't do anything, really, unless it really makes me laugh," he said.
Smith listed the names of Grant's past co-stars to get his reaction:
•Renee Zellweger - "Bridget Jones's Diary":
"She's a genius. You can't get a better actress. She's charming. She's a very good kisser. I couldn't call her sane, but she's utterly delightful. No one would call her sane," Grant said.
•Julia Roberts - "Notting Hill":
"Well, one of the most beautiful faces I've ever seen in my life. I used to sit on the set and just look at her, which freaked her out. But, yeah, what a beauty," he said.
•Drew Barrymore - "Music and Lyrics":
Drew Barrymore's Extraordinary Life
"So charming, you just want to take care of her," he said. "I felt fatherly towards her. That sounds wrong and 'pervy' since it's a love interest. But I think when you see her on screen, you just want everything to be okay for Drew."
•Sandra Bullock - "Two Weeks Notice":
"Wow, such a genius. I'm so please that had she got nominated for not one, but two Golden Globes because I think she never gets the critical response she deserves. She's just amazing," he said.
•Emma Thompson - "Sense and Sensibility":
"Very clever. Again, not very sane, but very brilliant," he said.