No one can play a grouch quite like Bill Murray, and he does so in “St. Vincent” with aplomb and skill. The grouch in question is Vincent McKenna, an aging veteran with scant funds and even scanter inhibitions. Within the first 15 minutes of the film, Vincent steals from an outdoor fruit stand, creatively insults a bank teller, has sex with a prostitute he’d previously impregnated, and gets extremely drunk; he then drives over his own fence and passes out on the floor of his squalid apartment. His hedonistic lifestyle changes, though, once he starts to babysit the son of his next-door neighbor, Maggie. Oliver, a precocious middle schooler, begins to teach Vincent about responsibility, and Vincent in turn teaches Oliver how to stand up for himself. The usual hijinks and life lessons ensue. It’s trite and predictable, but the actors manage to draw humor and pathos out of an uneven script.

{shortcode-0d22e33a0f89f535d964903b2aeef83ac5146bb9}

The movie’s primary flaw is its reliance on cliché. Almost every classic movie trope shows up: there’s a hospital wheelchair race, a family dinner, a tearful standing ovation, a reunion with a beloved pet, an onstage hug, an “I love you, Mom,” and even a “sometimes in life…” There are, of course, the requisite montages set to upbeat pop music. The plot twists are equally formulaic. Obstacles arise and are resolved in an almost mechanical manner, even to the point that it might be possible to work out the entire plot from the trailer.

Granted, plenty of movies thrive on cliché; predictability can create a sense of familiarity and comfort as well as a large profit margin. What makes it so off-putting in “St. Vincent,” though, is its unwieldy combination with “edginess.” The screenplay ricochets from formulaic sentimentality to unsettling harshness, apparently unable to find a middle ground. In one particularly uncomfortable instance, a scene of Vincent and Oliver racing wheelchairs is closely followed by one of Vincent viciously branding Maggie a “deadbeat mom.” Director and writer Theodore Melfi likely intended for the two extremes to balance each other out, but instead they produce the impression that scenes from two different movies are being patched together. This weird duality causes problems towards the end of the movie, when two of the darker plot lines are pushed aside and left entirely unresolved for the sake of an uncompromisingly positive ending. Comedies are completely successful when they commit to being mainstream crowd-pleasers or sharp-edged black comedies; they rarely succeed when they try to be both at once.

The film also feigns greater depth and originality by involving a religious theme: Oliver’s teacher is a tolerant Catholic priest who accepts all faiths in his classroom. Likewise, Oliver petitions to make Vincent a saint, on the grounds that regular, flawed people can be just as holy as martyrs. Adapting Catholicism for the 21st century is a surprisingly ambitious aim for a comedy, but it might have been carried out well; what frustrates it, though, is the tonal inconsistency. The sappiness of the movie clashes with its philosophizing, taking away any persuasive momentum it might have gained.

The movie also toys with the idea of taking on the issue of veteran care, but it never fully commits. Towards the end, something is made of the fact that Vincent is a decorated war hero who has been allowed to slip out of society’s reach; again, though, the issue is never fully explored, and the heavy degree of silliness makes it hard to approach the film as something with a political argument to make.

All of these issues speak to the fact that the screenplay is Melfi’s first effort: it’s ambitious, but often lacking in finesse. Even so, the movie is entertaining because it’s legitimately funny. The humor never devolves into the slapstick or the scatological, and the jokes are consistently clever. Even when a line falls slightly flat, it’s rarely a matter of bad taste or stupidity. The actors make the most of the writing, often delivering the material to perfection.

In fact, the cast is the film’s greatest asset. Bill Murray utilizes his impressive comedic and acting capabilities, making Vincent a believable, sympathetic character while retaining a degree of roughness. Melissa McCarthy also does an excellent job as Maggie: though known for loud, physical comedy, she demonstrates an impressive level of subtlety here. Mostly working as the straight woman to Murray’s comic, she creates a multidimensional character with real vulnerability. When given a moment of comedy, though, she nails it with understated delivery and expert timing. Naomi Watts’s character never transcends caricature, though. As the cliche “hooker with a heart of gold,” her Daka does little more than hobble around on leopard-print stilettos, berating Vincent in a bad Russian accent. She feels superfluous in the movie, just another illustration of Vincent’s degenerate lifestyle. The plot line about her pregnancy is another demonstration of tonal unevenness—the grimmer elements of it are referenced occasionally but never completely embraced or addressed. Still, despite its flaws, “St. Vincent” is a fairly enjoyable experience, neither a must-see nor a total waste of time.

—Contributing writer Charlotte L.R. Anrig can be reached at canrig@college.harvard.edu.