Viktoria Lloyd-Barlow’s Booker-longlisted debut begins on a bright, cool summer’s morning in the 1980s. A woman called Sunday whispers a Sicilian proverb, admires the fields that rise above her Lake District home and notices a stranger lying on next door’s lawn. This is Vita, her smart, inky clothes hanging on her elegant frame, her hands raised skywards, “as though waiting for expected gifts”. All the Little Bird-Hearts is a sharp, watchful account of the intense friendship that builds between these two very different women, and its fraught aftermath. Confident, charming, privileged Vita has moved to Sunday’s small town from London. Sunday, like Lloyd-Barlow, is autistic. Social interactions perplex her, and she is happier calming her twitching hands in the “dark and silky soil” of the greenhouses where she works. She believes there is “a universal code to be broken, a pattern to be understood”, and uses two books – a 1950s guide to etiquette and a book of Sicilian folk tales – to navigate life, often repeating their lessons in company. She favours white food, cannot read clocks, and turns down any drink that is not cold and fizzy. Vita is delighted with her quirky new friend, and Sunday bathes in the warm light of her attention. She and her daughter Dolly start visiting Vita and her husband Rollo for weekly suppers, where hare is marinated in wine, antipasti come from Fortnum & Mason and crisps and peanuts are served from a blue floral soup tureen (Sunday sticks mostly to bread rolls and champagne). Sixteen-year-old Dolly is eyeing life beyond her socially awkward mother and spends more and more time with the glamorous Vita. Soon Dolly is barely at home and Sunday, as so often in her life, is excluded. The sugar rush of her friendship with Vita sours as she – and the reader – start to wonder exactly what it is her “soft-feathered and sharp-eyed” neighbour is hoping to get out of the friendship. Sunday tells her story with thoughtful, matter-of-fact verve. She speaks of the “grateful and covetous way” hands greet warm tea, of the “undisturbed grease” that makes a caged magpie’s wings shine, of motherhood awakening emotions “both furious and tender”. Observations land with the startling yet welcome snap of good standup comedy, as Sunday examines social norms with quizzical trepidation. It’s thoroughly enjoyable stuff, but there’s always an edge: trauma, growing menace, the fear of loss felt by a mother whose daughter has been leaving her behind since the day she was born. As the novel advances via childhood flashbacks and a terrifying garden party, we see both the scars Sunday bears, and the cracks in the armour worn by the more artful members of the cast. Lloyd-Barlow, a first-time novelist who left school without any qualifications before gaining a degree then a PhD as a mature student, pulls it all together with real skill: this is a slow burner, but it never flags. The result is a tightly focused story, set almost entirely in two neighbouring houses on a quiet street, that’s also a gleeful skewering of social codes, a raw portrait of family life and a revealing account of neurodivergence. Sunday may shy away from attention, but Lloyd-Barlow makes her wary, vigilant and poetic voice the star in a mesmerising debut. All the Little Bird-Hearts by Viktoria Lloyd-Barlow is published by Headline (£18.99). To support the Guardian and the Observer buy a copy at guardianbookshop.com. Delivery charges may apply.