But after their first scene – in which he shoves her up against a wall and grabs her face – the actor was pleasantly surprised.
"She pulled it off," Reddick, acclaimed for his acting chops on HBO's The Wire, tells PEOPLE. "She really took it seriously. She was committed to proving that she could do this."
In the movie due out in January, Carey plays a waitress named Krystal, who tries to escape her abusive husband, portrayed by Reddick, by going on a road trip with two brothers.
Says the actor: "I saw all the subtlety in her work, and it's really beautiful."
Adding that Carey is "very sweet" in person, Reddick says, "After this, I think she's going to have a film career, if she wants one. She is good."
Also good? The success of Reddick's FOX show, Fringe, where he plays a no-nonsense Homeland Security officer.
But, says Reddick, "We goof around a lot," noting that Dawson's Creek alum Joshua Jackson is a a big jokester.
TIdbits for Lost FansAs for J.J. Abrams's other conspiracy-laced hit, Reddick – who plays Matthew Abbadon, a creepy figure who's supposedly a lawyer – just finished filming an episode of Lost in Hawaii.
Any hints? "I was with Terry O'Quinn throughout the entire episode," says Reddick, referring to the actor who plays enigmatic island leader John Locke.
Asked whether he's a good guy or a villain on the show, Reddick says, "This show is so secretive that the only thing I can say is that, whatever may happen in the show, Abbadon definitely thinks he's a good guy. He's convinced that he's on the side of the angels."