A pair of young women working as contract killers in order to support their taste for fun vacations and fashionable attire might seem a good premise for a cheeky movie—and the opening sequence of “Violet & Daisy,” in which Saoirse Ronan and Alexis Bledel, dressed as pizza-delivering nuns, take out a whole gang of mobsters has a certain insouciance, even if it’s visually rather chaotic. But this first film directed (from his own original script) by Geoffrey Fletcher, who penned the adaptation of Sapphire’s “Push” that served as the basis for “Precious,” doesn’t deliver on the idea; it quickly becomes less a cousin to “Kick-Ass” than a tedious talkathon that might have closed off-Broadway after a single performance.

The problem is that after that opening gambit, the duo, having celebrated Daisy’s eighteenth birthday, go off for a much-needed hiatus, only to find that they need funds to buy the newest Barbie Sunday dresses. So they accept an assignment to kill a fellow named Michael (James Gandolfini) who’s invited execution by stealing a bag of mob money. When the girls get to his apartment, however, they find him gone and fall asleep. They awaken to the sight of the morose man sitting opposite on a chair, quietly inviting them to shoot. It turns out, of course, that Michael is terminally ill, and is trying to commit what amounts to suicide-by-assassin.

At this point “Violet & Daisy” becomes a sort of existential dialogue in which the three characters reveal their personal demons (Michael is estranged from his daughter, Daisy is in need of family connection, and Violet must be in charge). But conversation alone isn’t enough, so Fletcher keeps inventing incidents to bide time before his denouement. The girls run out of bullets and Violet goes off to buy some at a local store, where she’s caught up in a confrontation between two hostile gangs. And while she’s away, Michael’s apartment is invaded by another bunch of thugs who’ve been sent to finish the job the girls haven’t. Later, a sniper is revealed to be on hand to take the girls out if they don’t complete their task.

“Violet & Daisy” starts out as edgy comedy and, though it comes across more like “D.E.B.S.” than “Kick-Ass” in that respect, early on it holds one’s interest, especially since both Ronan and Bledel have a degree of charisma. And Gandolfini uses his hangdog manner to good effect as Michael, who—among other things—actually bakes cookies for his guests. There are also nice turns from Danny Trejo as the girls’ boss and Marianne Jean-Baptiste as that last-act sniper. But though it doesn’t even run ninety minutes, it’s coasting on fumes long before it ends. Neither as writer nor as director is Fletcher able to sustain his conceit to feature length. The artificiality of the movie eventually becomes too much to bear, and it expires as surely as one of the girls’ victims.