It’s hard to get good help, right? If so, a posh São Paulo household has a real gem on its hands in Val, the devoted, longtime family maid. Val waits on an idle husband and haughty wife hand and foot. She’s a warm, cuddle-dispensing nurturer to the couple’s sweet but feckless and needy son. Confined to a stifling back room in her off-hours, Val cheerily makes hard work look easy and never complains. Isn’t she just like part of the family?

Well, not quite. A fateful visit leads Val (Regina Casé) to this harsh realization. When her daughter, Jessica (Camila Márdila), arrives from the sticks for a short stay, what should be an uneventful stop fast turns into a domestic upheaval. Cozy relationships will be rocked, authority will be tested, and roles will be questioned. With a perceptive if sometimes heavy hand, the film sizes up the touchy boundaries between buddy and servant, old-fashioned deference and modern expectations of equality.

The Second Mother offers a fascinating glimpse into a milieu we don’t often see, the pampered upper middle class of contemporary Brazil. Val (Regina Casé) caters to Barbara; her husband, Carlos (Lourenco Mutarelli); and teenager Fabinho (Michel Joelsas) nonstop. Their rapport is lively and informal; hugs, kisses, and banter fly nonchalantly back and forth. It’s easy to see how the lines could blur between factotum and friend in this environment, which for all its mod furnishings and trendy aspirations harbors some distinctly old-school notions about knowing one’s proper place.

Behind her jolly, no-nonsense exterior, Val conceals a longstanding heartache: To serve her host family and raise Fabinho, she has been forced to leave her own daughter behind in the provinces for more than a decade. Val doesn’t really know Jessica, and when she arrives, the mother is startled by the daughter’s bold self-assurance—this girl is no meek country mouse. Jessica is unabashedly sure that she’ll pass the big city’s competitive university exams (the family condescendingly begs to differ). Encouraged by Carlos, she commandeers the house’s guest suite, turning up her nose at sharing Val’s tight quarters. Carlos and Fabinho gravitate toward Jessica for different reasons of their own, while Barbara rankles at the attention given the newcomer. Tension in the household builds. When Val begs her daughter to pipe down and keep a low profile, not only does Jessica disobey, she scoffs outright at Val’s subservience.

The men aside, the family drama really shapes up as a contest of wills between three strong women, and the cast’s confident acting gives heft to redoubtable characters. Karine Teles constructs a vain prima donna viewers will love to hate as Barbara, whose initial generosity curdles into vindictiveness when she feels the household’s balance of power shifting. We can’t help but feel her insecurity (and her bafflement at Jessica’s effrontery, which in fairness can cross the line into provocation).

Casé and Márdila received joint acting awards at Sundance, and their contrasting styles complement each other handily. Breezy Márdila plays off the expressive, expansive Casé, who is a huge star in Brazil. The more famous performer’s turn at times verges on over the top, but brings feeling and backbone to a character whose values are forced into an uncomfortable reckoning. All the actresses would have been better served by the cinematography, which features a lot of medium two-shots. When a close-up of these intense faces comes along, it provides a welcome visual relief and a deeper look into souls at war.

The Second Mother founders on a couple of false endings and concludes with a rather implausible feel-good resolution. But along the way, the film has been unafraid to engage with powerful material, revealing clashes of big ideas carried out on a domestic scale. The Second Mother offers a vigorous, satisfying new take on the delicate relationship between the server and served in today’s world—a world that hasn’t changed as much as it likes to believe.