Hollywood loves a comedy about a plucky kid and an aging eccentric. It also loves a drama about a child in danger. Starring Susan Sarandon as Sylvia, a chain-smoking, sharp-tongued, first-time foster parent to spirited eight-year-old Emily (Everly Carganilla), “The Accompanist” tries to be both. It also tries to do a whole lot more, not always successfully. One of the miscalculations of this often appealing but ultimately disjointed dramedy — the feature directorial debut of “Silicon Valley” star Zach Woods — is that viewers will root for Sylvia and Emily to remain a family, even as the former reveals herself to be a less-than-suitable caretaker. Side by side, they make a fierce, somewhat madcap duo. We feel for them, laugh with them, and yearn for their happy endings, until Sylvia’s failings throw the movie off balance.

We begin by hewing closely to Emily, a New Jersey child who lives with her grandfather, Martin (Kevyn Morrow). He’s a loving guardian, clearly devoted to Emily even as he grapples with signs of dementia. The pair have developed ways of coping with Martin’s memory loss; he leaves notes for himself around the house, while Emily keeps track of her own schedule. It’s only once Martin mistakenly drives them onto an active railroad track that the film introduces a troubling possibility: Emily may no longer be safe under his care.

From there, things move quickly. Sarah (Aubrey Plaza), a frazzled child protective services agent, yanks Emily from her home and delivers her onto the doorstep of Sylvia, a meshuggeneh who introduces Emily to pierogis, piano and practical jokes. After some initial skepticism and a couple of runaway attempts, Emily warms to Sylvia’s antics, and even expresses a tentative hope that she can live with her indefinitely.

That shift arrives around the film’s midpoint, which Woods — who co-wrote the screenplay with Brandon Gardner — marks with a moment of magical realism. Building on a recurring motif of witches, Woods has Emily and Sylvia lift off during a thunderstorm, soaring above the city skyline in a sequence that hovers between dream and fantasy. The image is meant to feel liberating, even transcendent, but it’s overly precious, interrupting the story’s grounded rhythm.

More confounding still is what follows. Immediately after alighting from its fanciful detour, Woods makes the odd decision to leave Emily’s perspective and lock into Sylvia’s. At the same time, it introduces a new threat to the pair’s fragile arrangement: Sylvia’s unresolved grief over her daughter, who died years earlier. By this point, Emily has already grown attached to her new foster mom. But once Sylvia finds herself returning the girl’s affection, the trauma of losing her daughter resurfaces and her guard snaps up.

Woods illustrates Sylvia’s sorrow through flashbacks to her daughter, Nadia (Olivia Edward as a teenager, Emma Farnell-Watson as an adult), who was a ballet dancer. Those scenes are fine on their own. The real trouble occurs when Sylvia’s pain manifests in the present, where it gets expressed as mistreatment of Emily. Practically overnight, Sylvia’s cozy attitude toward the girl hardens into coolness, impatience and neglect. Bewildered by the change, Emily scrambles to restore their bond, implausibly teaching herself piano in a bid to impress her guardian. As Sylvia continues to rebuff her, the child grows miserable, then desperate.

By focusing on Sylvia’s emotional wounds, “The Accompanist” not only leaves viewers upset on Emily’s behalf, but also shrinks its ambitions. What begins as a story about systemic failures — the difficulty of childcare, the shortcomings of the foster system — contracts into an account of one woman’s trauma response. It also leaves the film carrying a surprising amount of psychological baggage, with enough emotional reversals to keep viewers’ heads on a swivel. Woods often uses comedy to lighten the load, and sometimes — especially in scenes with Plaza — pulls off the tricky feat of finding humor in serious or even dire situations.

Alongside the comedy, the performances from the two leads prove the movie’s saving grace. Sarandon brings a welcome unpredictability to Sylvia, complicating a character who might otherwise have curdled into cliche. Her fierce intelligence helps paper over some of the screenplay’s rougher transitions, and even lends a measure of legibility to Sylvia’s sudden coldness. Carganilla, meanwhile, is uniformly astonishing, a bright beam of feeling who charts Emily’s arc from hopeful to anguished with a conviction beyond her years. Fragmentary and uneven, “The Accompanist” itself might not break your heart, but its talented young star inevitably will.