Sometimes a serviceable story is elevated by a masterstroke of casting. In “Hope Springs,” it’s two masterstrokes.

The story concerns a husband and wife whose 30 years together has curdled into deadening routine. Arnold is a grumpy accounting executive whose day revolves around not interacting with his wife, Kay. She wistfully wishes to recapture their marriage, but being a timid soul, she hardly knows where to begin the salvage process. They attend marriage counseling, talk about their issues and begin rebuilding.

So far, so what. Except the no-longer-happy couple is played by Meryl Streep and Tommy Lee Jones in wonderfully committed performances.

Directed by David Frankel (“The Devil Wears Prada”), the film deals knowingly with a marriage that has drifted into tedious routine. Sweet, supportive Streep serves Jones one egg sunny-side-up and a bacon strip every morning. He eats without glancing up from his paper and scoots out the door without so much as a peck on her cheek. He juggles numbers in his office, and she folds sweaters at a clothing store. Each night, he conks out in front of golf programs, and they retire to separate bedrooms.

They live like two recluses under the same pleasant middle-class roof. There are no fireworks. Each is studiously polite and determined to avoid friction. You would expect the sameness of their lives to grow dull, but two of America’s finest actors tiptoeing around each other is a sight to behold. Streep can steal a look at Jones and make her eyes whimper. Jones, politely keeping his wife at emotional arm’s length, distills his trademark irascibility to the essence of discomfort.

The film is naturalistic and low-key. Much of it follows their trip from Omaha to Maine for a week of intensive counseling. Steve Carell plays it utterly straight as the celebrity therapist who assists them in renewing their commitment. The film’s best scenes are top-drawer actors speaking unremarkable lines while extracting every drop of meaning from them.

Jones rankles at Carell’s assignment to talk about his feelings and fantasies – his evasive replies and ill-at-ease body language are eloquent far beyond his plainspoken dialogue. Streep’s character is not the vibrant, sure-footed type she often plays. Here she portrays a mild-mannered, nondescript frump – and does it brilliantly. She’s often a half-step behind the conversation. When Carell asks her a direct question about her sex life, her befuddled “Huh?” is explosively funny.

The film is a dual character study aimed at getting couples in the audience to open up and talk to each other. As the story unfolds, Streep’s character slowly gathers strength, and Jones tentatively sheds his suit of armor. The finale is a jolt of sweet optimism and relief, but you realize they’re still a long way from “death do us part,” and every mile of that road will take effort. It’s not so much a happy ending as a new start.