From left, Dani Nefusi, Naomi Nero, and Matheus Nachtergaele in Don’t Call Me Son (Zeitgeist Films/Aline Arruda)

When a teenage boy discovers his mother is not his real mom after all, the bombshell revelation throws his existence into turmoil. Families will be broken and reassembled. An unfamiliar new life will begin. As she did in last year’s The Second Mother, Brazilian director Anna Muylaert takes on social class, shifting identities, and what happens when a newcomer knocks a family dynamic off balance. She also throws in cross-dressing and oodles of sex. But while The Second Mother bubbled with energy and ideas, Don’t Call Me Son simmers on a morose low boil. For a story hinged on a startling DNA discovery, it’s an oddly bloodless affair.

Pierre (Naomi Nero) leads a charmed life, although not an upscale one. The doe-eyed teenager plays in a crappy rock band, gets a thrill wearing women’s nail polish and dresses, and enjoys his share of sex from both boys and girls thanks to his louche, dark good looks. He enjoys a relaxed rapport with his slapdash, affectionate mother (Dani Nefussi) and his younger sister in their modest apartment. The comfy ménage comes crashing down, though, when a police investigation and a DNA test reveal that Pierre’s mother is not his biological parent but a thief who stole Pierre from a wealthy couple (Dani Nefussi again, in an unobtrusive example of double casting, and Matheus Nachtergaele). The couple’s been looking for Pierre for years, and they’re over the moon at having him back. But how will his wild ways fit into their controlled, immaculate household?

A lot happens in Don’t Call Me Son. Pierre’s mother is jailed, his sister remanded to the care of another family, and Pierre and his aunt smash dishes in a rage. Pierre soon clashes with his new parents and brother, who have their own anxieties and communication failures exposed by his arrival. And, of course, Pierre seduces not one but two girls at once in his tony new high school. But for all this business, somehow Don’t Call Me Son feels like a series of punches flying but not landing or an oar that fails to pull a skiff in the water.

Part of the problem may lie with a walled-off, opaque main character. As Pierre, Nero wears the same expression on his face whether he’s getting laid, fighting with his new dad, or taking selfies of his ass in the mirror. Is this a case of limited acting or a convincing depiction of an alienated too-cool-for-school teen? Tough to tell, but it’s hard to warm up to Pierre. His new family doesn’t elicit much love either; we want to sympathize with their struggle to reach him, but they come on so overbearing and insensitive that we recoil along with the young man. An episodic approach to the narrative and straightforward, washed-out cinematography further deflate what really ought to be a more moving and intense story.

A scene in a department store changing room administers a bracing shock (and the movie’s one moment of humor). The film ends with a tentative rapprochement between brothers, tenderly observed. So it’s a pity more moments like these couldn’t enliven a subdued project, which somehow can’t convey the depths of feeling that obviously went into its creation.