THE PERFORMANCE

With her straggly blond hair -- a few months late on a dye job -- and messy makeup, Helene McCready is a tornado of hurt and mistrust in “Gone Baby Gone,” Ben Affleck’s directing debut opening Friday. The world has given her a raw deal that’s only gotten worse with the kidnapping of her 4-year-old daughter. But she’s also a street-smart grifter, whose tears you’re never sure are real.

Helene was just the sort of character Amy Ryan wanted to slip inside of.

“I felt like I can do this,” says Ryan, recalling her emotions upon reading the script written by Affleck and Aaron Stockard based the novel by Dennis Lehane, who also wrote the novel “Mystic River.”

“I didn’t hate her. It was like ‘Oh, man.’ I was kind of thrilled by her in terms of an actor. You don’t think of a character as being the bad guy . . . It’s more like, “I can say that and do that and get away with it?’ ”

Set in the ethnically diverse, lower-middle-class Dorchester, Mass., “Gone Baby Gone” revolves around the search for Helene’s daughter. Affleck’s younger brother, Casey, plays Patrick Kenzie, a young private investigator hired to help the cops find the child.

The Queens native, who received Tony nominations for “Uncle Vanya” and “A Streetcar Named Desire,” has a good deal of empathy for Helene.

“Of course, Helene McCready is not a good mother,” says the petite, unaffected actress. “But where are the systems that aren’t in place in neighborhoods like Dorchester? They need a hand. Helene is a single mom who is not educated, drug addicted, an alcoholic. No healthcare. No child care. She never had love. The little daughter that we have such fear and hope for in this film -- Helene was also that little girl. It’s not an individual problem. It’s a societal problem.”

When she got the role, Affleck told Ryan that he wanted her to blend into the neighborhood. “He said, ‘I want people at the end of the day to ask me where did I find this local from Boston?’ That’s the thing that scared me the most. That was a great challenge.”

Understanding Helene’s world came with its own challenges. Before filming began, she spent time in a Dorchester bar that was one rung up the ladder from the dark dives that Helene haunted. “The bartender leaned over and said, ‘What are you doing here? . . . There have been seven shootings in the neighborhood in the last several days.’ I thought, ‘Maybe I should go back to the hotel.’ ”

She honed her Boston accent and gritty attitude by hanging out with several neighborhood locals that Affleck hired, as well as by eating lunch with the Teamsters on set. Ryan had strong ideas about Helene’s appearance. “I think before her child was kidnapped, she looked pretty good -- her version of it -- but I don’t think she’d washed her hair and face for three days. Her makeup would have fallen and smudged. And she’ll have greasy hair.”

But it was Affleck who picked out the tacky bubble-gum-pink fingernail polish. “I remember they handed me, like, five different colors,” she says. “Ben said, ‘That one’ because it was the Dorchester color.

“I think sometimes we played this part together,” Ryan says. “He kept pushing me . . . . He said ‘Amy, trust me. I know Boston. I know this world. So if I push you all the way to the left, trust me.’ ”

susan.king@latimes.com

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Where you’ve seen her

You might recognize Amy Ryan from her turns on TV, where she’s been a regular on HBO’s “The Wire” and A&E;’s “100 Centre Street.” She’s also had roles in such films as “Keane” and “Capote.” Look for her in the upcoming “Before the Devil Knows You’re Dead” and “Dan in Real Life.”