The success of last year’s Superman film proved there was still some interest in comic-book movies, all these years into their Hollywood-blockbuster dominance. The director James Gunn reintroduced viewers to the aw-shucks costumed champion, this time trying to make a name in a cynical, contemporary landscape, and Gunn’s approach made the classic superhero ideals of truth and justice feel fresh instead of corny. Tucked into the story was another caped crusader: Superman’s chaotic cousin, a hungover and bedraggled 20-something possessing none of his goody-two-shoes poise.

This was Supergirl (played by Milly Alcock), and now she is getting a movie of her own. Part of the new crop of DC Comics movies, this latest installment is designed to build out a wider, interconnected franchise, much as Marvel did years ago. DC already unsuccessfully tried to expand its cinematic footprint a decade ago, with a grim and muddy trilogy from the filmmaker Zack Snyder. Supergirl, directed by Craig Gillespie, swings at the brighter tone Gunn brought to Superman. If Superman is the ultra-responsible face of the franchise, Supergirl is supposed to be his messier, relatable counterpart. Yet Alcock’s charming performance cannot elevate Supergirl beyond franchise filler—a disorganized character study meant only to extend a universe.

Supergirl is, on paper, aiming for something knottier than a typical comic-book adaptation. The titular hero was born on the doomed alien world of Krypton, growing up in a shielded city that managed to survive the planet’s initial destruction. When that last bastion falls and she finally arrives on Earth in a spaceship, she’s a teenager mourning a family and civilization she knew and loved—as opposed to her cousin, who departed as a baby and has no memories of his home world. Supergirl’s grief sends her binge drinking across the galaxy to dull the pain of losing Krypton.

Read: All end-of-the-world menace, all the time

Looking at his previous work, I can understand why Gillespie was hired for the gig. For Cruella, he was handed another piece of female-centric intellectual property by Disney, making a complex figure out of a classic cartoon villain. Before that, he directed I, Tonya, a biopic that tried to untangle the backstory of a much-scrutinized antihero, the ice skater Tonya Harding. But Supergirl doesn’t quite want to deal with the immensity of its protagonist’s feelings; her drunken stupor is often played for laughs, defined by bedraggled hair, big sunglasses, and plenty of slurred speech.

That’s the state Supergirl is in when she is dragged into a local dispute on some far-off planet, defending the honor of an orphaned teenage girl, Ruthye (Eve Ridley); her parents were murdered by a brigand named Krem of the Yellow Hills (Matthias Schoenaerts). When Supergirl’s boisterous dog, Krypto, is imperiled during the fracas, she and Ruthye must hunt Krem down to save him. Superman pops in for a couple of cute scenes along the way, while another DC side character, the alien and bounty hunter Lobo (Jason Momoa), appears as a tortured bit of universe-building. All of this business, however, gets in the way of providing Supergirl herself with a fulfilling storyline.

The script, by the playwright Ana Nogueira, is a close adaptation of a fairly celebrated comic-book series called Supergirl: Woman of Tomorrow. The wild sci-fi elements, such as scummy aliens and wacky monsters, will likely remind audiences of a Marvel effort, namely Gunn’s Guardians of the Galaxy movies. Supergirl has good reasons to avoid Earth—she feels overshadowed by her widely beloved cousin and disconnected from the humans he’s protecting—but there’s little sense of place to the various CGI-rendered landscapes she travels through. That geographic blandness only emphasizes the film’s other shortcomings, such as Schoenaerts’s anonymous work as the villain (a lot of glowering and creepy glares) and the rather rote big-sister/little-sister arc given to Supergirl and Ruthye.

Despite the darker notes Gillespie seems to be searching for, Supergirl repeatedly insists to Ruthye that she should avoid seeking revenge, because doing so would change her inexorably—a warning Ruthye heeds even as the pair is playing an interplanetary cat-and-mouse game with the murderous Krem. The movie basically imports Superman’s moral code, which doesn’t really jibe in a story filled to the brim with cigar-chomping bounty hunters and outlaws. As a result, Alcock must abruptly perform different types of emotionally varied material—goofy comedy, heroic duty, and her character’s tragic origin story. That’s a shame because she’s clearly capable of handling all of it. Supergirl the character still has a lot going for her, presumably including a future in the DC Universe. Supergirl the film, meanwhile, is only a mildly diverting whiff.