The new Brazilian film “I’m Still Here” begins with images often associated with the country: the gorgeous grin of Rio’s shoreline, totemic Sugarloaf Mountain, beach volleyball, and sunbathers galore. Yet this idyllic vibe comes under shadow briefly, when a military helicopter cuts through the air above our heroine, Eunice, as she’s floating on her back in the water. A little later on, another disturbance of the blissful ambience occurs when Eunice’s teenage daughter Vera and three of her friends encounter a police checkpoint while driving through a city tunnel.

The year is 1971 and Brazil has been under a military dictatorship since 1964. Eunice and her husband Rubens Paiva, a former congressman turned architectural engineer, live across the street from the beach in a large house with their five children and a live-in maid. Television news segments report a kidnapping by liberation forces who demand the government release political prisoners, but the overall mood in the Paiva household remains one of hospitality and joy as the kids and their friends scamper or lounge about and the adults entertain their intellectual, affluent compatriots.

Director Walter Salles takes great pains to establish this almost utopian homelife not only to provide a contrast with what will come later, but also because he experienced it first-hand. Based on the memoir written by Marcelo Rubens Paiva, the son of Rubens and Eunice, and Mr. Salles’s own adolescent memories as a frequent house guest, the film revolves around the real-life disappearance of the Paiva patriarch due to “subversive” activities. Both detailed and ambiguous, the elegiac movie occasionally works as a memorial of a particular time and place, yet its story never really takes shape beyond the before-and-after of the abduction, leaving the film detached and sluggish, akin to watching a slideshow instead of a moving picture.

After the careful setup of the Paiva milieu, the nightmare arrives one sunny day when plainclothes officers come to take Rubens away for questioning. In tense scenes, Mr. Salles stays with Eunice and the kids as they become prisoners in their own home. The next day, she and second-oldest daughter, Eliana, are also brought in for questioning. As an interrogator makes the accusation that her husband consorts with terrorists, Eunice maintains her composure even as her body trembles with fear. Soon, she’s thrown in a prison cell, where she’s kept for nearly two weeks without ever being charged with a crime.

Once Eunice returns home, she enlists a lawyer to find out about Rubens’s whereabouts, even as the government denies he was arrested during the crackdown. Mr. Salles, though, isn’t interested in turning the movie into a missing-person conspiracy mystery crossed with a legal thriller, despite a few gestures in that direction. Instead, the director focuses on the mother and her efforts to keep her family safe and relatively sound, though the tasteful character study meanders when it should create a pathway. 

While Mr. Salles is to be commended for resisting the urge to sensationalize the material, he also evades a true reckoning with Rubens’s disappearance — particularly by the Paiva children, who are all sketchily drawn. Only Eunice emerges as a fully fledged persona, one brought to beautiful, gentle life by actress Fernanda Torres. With the exception of a couple of times in which the character releases some pent-up rage, her performance is a study in grace under pressure and positive determination in the face of trauma and tragedy.

Soon after Eunice is told of Rubens’s death, she takes the uninformed children to an ice cream shop the family visited earlier during the movie’s halcyon opening section. It’s a crushing scene emotionally, as she looks around at the other families and friends. Yet Eunice does not break down, keeping it together for her kids’ sake. In moments like this, the acting by Ms. Torres is the epitome of what could be considered awards-worthy, and the film consolidates around the themes of loss, grief, and remembrance. 

When the movie shifts to 1996 in its third act, the narrative loses additional energy. In the interim, Eunice has become a lawyer and we see her give a lecture on the rights of indigenous people — yet we’re never shown how the real Mrs. Paiva’s advocacy led the now-democratic government to acknowledge the brutality during the dictatorship. 

Serving as the movie’s climax, though there’s no build-up to it at all, is the moment when Eunice receives an official document certifying Rubens’s death. When asked by a reporter if the government has better things to do than reconcile with formerly sanctioned acts, she responds with a smile and goes on to say that if forgotten, the crimes of the past will continue to be committed.

While Eunice’s answer is noble and righteous, the film ultimately fails to turn the tragic tale of the Paiva family into vital storytelling, such as would make us feel the shock of a family robbed of its innocence and a country stained by political violence. Perhaps the director was too close to the material to truly examine it, or too reverent to the “true story” to mold it into compelling cinema. A cloying, insignificant epilogue involving Fernanda Montenegro, the mother of Ms. Torres who starred in the great 1998 Salles film “Central Station,” only exacerbates the sense of a missed opportunity.