A mother sits in the front seat of a car, her tanned and freckled face glowing; her daughter, owlish and opaque behind her glasses, stares at her mother’s cheek, transfixed, as the countryside glides by. The camera tracks the daughter’s gaze—what she sees is all that matters. Later, at home, the eleven-year-old girl practices on her tinny keyboard (plink-plink-plunk), ignoring the roaring cicada symphony outside.

That obsessive, catalyzing, world-building attention is the subject of Annie Baker’s début film, “Janet Planet.” It follows a single mother, Janet (Julianne Nicholson), and her daughter, Lacy (Zoe Ziegler), through a hot, green-and-brown-grass summer in western Massachusetts, in 1991. The pair orbit each other—Lacy wants to hold her mother’s hand when she falls asleep, or to keep a strand of her hair—but they are also as lonely as satellites.

“I’m actually pretty unhappy, too,” Janet says to Lacy, abstractedly. Until now, Baker has been known as a playwright. Her generation-defining plays—including the gently humanist “Circle Mirror Transformation”; the Hollywood-is-hell comedy “The Antipodes”; “John,” in which a relationship founders in a doll-infested bed-and-breakfast; and last year’s chronic-pain narrative “ ”—are famous for their micro-naturalistic dialogue and carefully timed, hypnotic languor.

Her approach, which reminds me as much of Cassavetes as of Chekhov, has exerted enormous influence: one can sense her imp.