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The thrills in The Other Side of the Street have little to do with the alleged crime that’s at its center. What’s rather more exciting in Brazilian director Marcos Bernstein’s debut is its portrait of senior love—and not the faux, Hollywood kind presented in 2003’s Something’s Gotta Give, which patted itself on the back for daring to show a then-56-year-old Diane Keaton as an object of desire.

Here, genuine geriatrics get frisky: Raul Cortez, 72, and Fernanda Montenegro, 75, play Camargo and Regina, neighbors who begin a romance after the film’s Rear Window–esque setup brings them together. Cortez’s age may not be remarkable to American audiences accustomed to seeing the likes of Clint Eastwood and Sean Connery in one not-dead-yet role after another. But when was the last time you saw a septuagenarian actress play anything other than a nursing-home patient or a convenient comic foil?

Perhaps even more surprising, Cortez is only a supporting player. The Other Side of the Street belongs to Montenegro, whose Regina is a lonely Rio de Janeiro grandmother who spends more time with her dog than her family. To keep herself occupied, she volunteers as a police informant, hanging out in Copacabana clubs and spying on nearby apartments with binoculars. Some of her tips lead to newsworthy busts, including the takedown of a child-prostitution ring. But when she reports seeing Camargo, a former judge, seemingly murder his wife with an injection, her contact, Officer Alcides (Luiz Carlos Persy), not-so-gently suggests that Regina go back to looking after her own life.

The script, co-written by Bernstein and Melanie Dimantas, is spare to the point of starkness, and the first third of The Other Side of the Street moves as slowly as a retiree’s day. Regina doesn’t interact with other people much, speaking only to vendors, her pooch, or, occasionally, her grandson. She often just sits in her apartment sighing and saying “Oh, God” a lot, as desperate as we are for something to engage her. (Guilherme Bernstein Seixas’ mournful, repetitive piano-and-strings score doesn’t help.)

Clearly, she needs to get out. And when she does, walking around and witnessing the petty crimes all around her, it becomes clear that this has always been Regina’s calling. Cinematographer Toca Seabra captures Rio in all its bustling, beachy sophistication, and Regina never seems as pathetic outside and on the case, blending into the fast-moving metropolis outside her door. Things get especially interesting when Rio’s Miss Marple begins to follow the handsome Camargo around town. (The judge, in one of the scriptwriters’ less graceful orchestrations, takes to shading his window only after his wife’s death, forcing some up-close-and-personal surveillance.) The remainder of The Other Side of the Street becomes an intriguing cat-and-mouse dance that shifts the movie’s primary concern from Did he do it? to, well, Will he do her?—an unsubtle narrative development that Montenegro and Cortez redeem with surprising deftness.

Yes, both characters gently acknowledge their mileage as things get more involved—referring to stretch marks, say, or not knowing the finer points of modern courting. And the interactions between them are indeed more charged than those of many a rom-com couple half their age. But it’s the way Regina’s essential isolation and invisibility hover behind this relationship that makes it interesting. No gray-haired slouch, she takes care to be fashionably dressed and made-up—even if, giving herself a kiss in the mirror after she puts on her lipstick, she’s her own best admirer. And the disapproval she displays for everything from the domino-playing geezers in the town square to Camargo’s life-goes-on behavior after his wife’s death reveals more than just a deep cynicism about her fellow seniors. (“If you prefer to sit at a table waiting to die…” Regina snaps when another snitch suggests she not take the work so seriously.)

Montenegro, the star of 1998’s Central Station (which Bernstein also co-wrote), masterfully reveals her character’s stricken pride in bursts of pursed lips and stony silences. Cortez’s Camargo, meanwhile, is an ably played balance of sensitivity (when speaking of his wife) and brusqueness (when putting the moves on Regina), which helps keep the question of his guilt constantly up in the air. Add in Regina’s nearly imperceptible change in attitude toward her widowed neighbor—it’s difficult to tell when her interest in him turns from investigative to romantic—as well as her hard-to-maintain lie about where she lives, and The Other Side of the Street becomes much more fascinating than the mere whodunit it initially seems headed toward. And, in contrast to Something’s Gotta Give, the actors’ twilight demographic is not a gimmick but a simple fact—proving that even on the silver screen, age ain’t nothin’ but a number.CP