Butler, regrettably, hasn’t done a lot of small-scale indie dramas — ones you find in the program of the Un Certain Regard section at Cannes. But “Dear Frankie” is so good that it’s worth a whole career of them. Directed by Shona Auerbach from a script by Andrea Gibb, the film boasts subtlety, a sense of place, and a generous spirit — matching the best of British working-class cinema.

The plot follows Lizzie Morrison (Emily Mortimer, also in one of her best film roles), a mother who brought her nine-year-old deaf son Frankie (Jack McElhone) to the coastal town of Greenock, Scotland to steer clear of her abusive ex-husband. Without the heart to tell Frankie the truth about his father, Lizzie claims he’s working far away as a merchant seaman. Through a series of coincidences, Frankie believes that his father has finally come to see him, forcing Lizzie to enlist a man known only as The Stranger (Butler) to pretend to be Frankie’s dad for one day.

Although that logline could have made for something schlocky or sensationalist, “Dear Frankie” is never less than honest and deeply-felt. This film allows Butler to sink his teeth into a stunningly understated and complex role. It’s comfortably the best live-action film of his career, and a reason to hope he returns to the arthouse drama world in the future.