Love may be at the heart of Ain’t Them Bodies Saints (out today), but for Rooney Mara, one half of the film’s star-crossed pair, picking out what makes great love is no easy task. “There’s so many great American love stories, but I don’t know what the common thread between them all is,” she admitted to InStyle.com at the film’s New York premiere Tuesday. “I guess great characters, two great characters.” In the drama, devoted Bob Muldoon (Casey Affleck) seeks to reunite with wife Ruth Guthrie (Mara) and their daughter after four years in prison — Muldoon was arrested after taking the blame for his wife’s crime and escaped.  Journeying across 1970s Texas, Muldoon finds the path back and life he left are rough, especially as Sheriff Patrick Wheeler (Ben Foster) becomes a greater figure in his home. When picking the film’s Americana fashion, director David Lowery told InStyle.com he tried to create a fascinating blend of time periods, pulling pieces from throughout the 20th century. “We started in 1979 and just worked our way backwards and whatever felt appropriate for the character, we just sort of dialed it in that direction.” For Lowery, also the film’s writer, capturing great love is simpler. He sums it — and what makes Mara and Affleck’s duo so compelling — in one word: “Sincerity.” Catch Ain’t Them Bodies Saints in theaters now.

Plus, see Rooney Mara’s best looks ever.

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— Alyssa Bailey