Soap opera meets rock concert in Jonathan Demme’s “Ricki and the Flash,” which also confirms the old adage that most musicians want to act and most actors want to be musicians. The oddly bifurcated movie offers sporadic pleasures, but as a whole it just doesn’t gel.

Meryl Streep continues the singing career she’s embraced in “Momma Mia!” and “Into the Woods”—as well as adding some dexterity on guitar—in playing Ricki Rendazzo, lead singer in a cover band called The Flash, which has been a staple for years at a Los Angeles watering hole. Among the other four players, all of them graying, is Greg (Rick Springfield), the guitarist who’s obviously in love with her though she resists getting too close to him offstage and sometimes even insults him in their onstage banter.

Ricki’s never made it in the business—she barely makes ends meet working as a cashier in a trendy food mart—and her wild ways and modish attire camouflage an essentially conservative political bent—she keeps a living room shrine to a brother who died in Vietnam, has a tattoo of an American flag on her back, and doesn’t deny voting twice for George W. Bush. But she seems a free, uninhibited spirit until she gets a call from Indiana that she avoids taking until the insistent ringing can’t be ignored.

It turns out that it’s her ex-husband Pete (Kevin Kline), bringing news that their daughter Julie (Mamie Gummer, Streep’s real-life daughter) is suffering debilitating depression after her husband announced his intention to get a divorce. Ricki hops a plane to visit the girl she hasn’t seen in years, even though it means getting to Indianapolis broke. Though Julie berates her brutally at first, Pete’s courteous and kind in a typical Midwestern way (even though, to be frank, the locations don’t look very Indianan), even giving her a guest room in his gated-community mansion while his second wife Maureen (Audra McDonald) is off in the Northwest visiting her ill father.

In the early L.A. scenes Demme, who’s always shown a penchant for rock, gives Streep ample opportunity to strut about the stage and demonstrate her vocal prowess. In the succeeding Hoosier portion of the film, however, she gets only one brief solo; Diablo Cody’s script takes over, and it proves to be nothing more than a supposedly acerbic but actually syrupy domestic dramedy in which the star must tearfully come to terms with the abandonment of her children—not only Julie but sons Josh (Sebastian Stan) and Adam (Nick Westrate). The former is welcoming, but Ricki (sometimes called by her given name, Linda) is hurt to learn he’s not only engaged to straitlaced Emily (Hailey Gates) but doesn’t intend to invite her to the wedding. Adam, on the other hand, is overtly hostile over Ricki’s reluctance to accept that he’s gay. Nevertheless Ricki has quick success with Julie, enticing her from her funk with a visit to a doughnut shop and a hair salon—a rescue from suicidal thoughts that’s too easy by half.

The best element of this long section of the film, anyway, is neither Streep nor the younger actors; it’s Kline, whose gentle prissiness is a delight to watch, even if he doesn’t come across as terribly Midwestern. It’s unfortunate that Cody gives in to one of the most prevalent of modern screenwriting clichés when she has Ricki, Pete and Julie indulge in some pot and get so mellow that Pete comes on briefly to his former wife. It’s a sequence that not only recalls many similar ones in other movies but gets a mite uncomfortable before it’s over.

The spell of domestic reengagement is broken, however, when Maureen returns, she and Ricki butt heads and Ricki heads back to California, where Demme stages more energetic musical numbers, though one is disfigured by an embarrassing riff on expectations about mothers and fathers that comes across as obvious and contrived. The twist here—and the strongest element in Cody’s otherwise conventional script—is that Maureen is no ogre of a stepmother but a thoughtful woman who sees to it that Ricki gets an invitation to Josh’s wedding. And after finally committing to Greg, she travels back to Indianapolis with him for the ceremony, where even though she’s treated as a curiosity by some of the other guests, she triumphs not only by encouraging Julie not to break down but by taking the stage with her band to give the newlyweds a musical gift. With all the dance moves that ensue, you’d think this was an Indian wedding in a Bollywood movie; the synchronized moves that the crowd has learned by the closing credits are frankly amazing.

By this time “Ricki and the Flash” has gotten to the point of eating its (wedding) cake and having it too. It ends with Cody’s soapy familial reconciliation—everybody on stage singing happily and Ricki even welcoming news that Adam has found a partner—while trying to remain true to Demme’s freewheeling rock spirit. That concluding mismatch is merely the culmination of the movie’s essential problem—the fact that its two parts never successfully mesh.

Still, it does boasts a big, blowsy performance from Streep, who tosses the subtlety that marked her early work out the window but throws every bit of her considerable know-how into her scenes both onstage and off (and delivers the goods vocally as well). And she’s game about wearing some really outlandish duds designed by Ann Roth. Kline makes a nice foil for her, with McDonald and Springfield providing strong support as well. It’s a pity that the youngsters don’t measure up to their seniors. Gummer looks right, of course, but her gloomy one-note turn doesn’t show much range, and neither Stan nor Westrate gets much chance to go beyond stereotype. Even Bill Irwin, who stops by for a single scene, is underused. The tech credits are just okay, though Declan Quinn’s fluid cinematography gives the musical sequences some visual pizzazz.

When it comes right down to it “Ricki and the Flash” is innocuous enough, but it doesn’t come near to what one has a right to expect from Demme, Streep or even Cody. Blandly conventional except for an occasional surge of musical energy, it goes down relatively easily but leaves no lasting impression.