It’s a sultry summer in the late 1990s and 13-year-old Grace (Niamh Walter) leaves her parents and their troubled marriage behind in London to visit Cornwall with her best friend Asta (Nyobi Hendry) and Asta’s boho-cool mum Kate (Rebecca Palmer). There are woods to mess around in, plenty of time to wonder what kissing boys will be like, and long-leash supervision from Kate who lets the girls run free. Nevertheless, the every-night’s-a-sleepover atmosphere is darkened by Grace’s menace-suffused dreams, rabbit corpses that keep popping up out of nowhere, and a handsome but intrusive male presence in the shape of Sid (Zaqi Ismail), who comes to visit. A shy, watchful only child who is having one of those adolescent religious phases, Grace is troubled by her knowledge of dad Rupert Shelbourne’s infidelity and her mother’s sorrow, but has also internalised her dad’s prejudice against “fat girls”. She looks primed to develop either an eating disorder or a drug habit, or maybe neither of the above. It’s that point in a life when everything is possible.

Director Alice Millar and screenwriter Isobel Boyce jointly evoke the sensuality and protean quality of 13-year-old girls, especially the delicate kittenish power struggles between friends over who is more sophisticated, but also who is more authentically a child. The period setting is especially useful here because, instead of spending all their time staring at their phones like most contemporary teens, these two are still interested in building dens in the woods. But they also want to decorate the structure with flowers: “I think it’s really important that it’s attractive as well as functional,” says Asta, clearly channelling mum Kate’s sensibilities. And while the warm, sun-flare-dappled cinematography is credited to Benjamin J Murray, Millar’s experience as a director of photography pays off with a strong visual identity that runs through everything, from the lighting to the warm orange hues in the costumes and production design.

Less assured, however, is Millar’s touch with the young actors; they struggle a bit to make the dialogue sound natural. Meanwhile, the film’s ambition to evoke a sense of dread, especially with a droning, almost John Carpenter-ish sort of soundtrack, doesn’t quite come off somehow, and the last act is maladroit and all over the shop. Still, it’s an interesting, promising feature debut for Millar, and Walter has real star presence.

• Summer in the Shade is available on 20 June on digital platforms.