Superficially, The Little Friend is a mystery adventure, centered on a young girl, Harriet, living in Mississippi in the early 1970s and her implicit anxieties about the unexplained death of her brother Robin, who was killed by hanging in 1964 at the age of nine. The dynamics of Harriet's extended family are a strong focus of the novel, as are the lifestyles and customs of contrasting Southerners.
In 2002, Tartt described it as "a frightening, scary book about children coming into contact with the world of adults in a frightening way... After The Secret History I wanted to write a different kind of book on every single level. I wanted to take on a completely different set of technical problems. The Secret History was all from the point of view of Richard, a single camera, but the new book is symphonic, like War And Peace. That's widely thought to be the most difficult form."
Harriet and her sister have been raised largely by their grandmother Edie, a bevy of adoring great-aunts, and the family's longtime housekeeper, Ida Rhew. (Robin's death sent the girls' mother into a dreamy depression from which she has never awakened, and their father lives with a mistress in Nashville, returning home only at Christmas.) Harriet, who looks like a "small badger," is the sort of child who likes to read about Genghis Khan and Captain Scott and to stir up fights among her great-aunts by telling them what they really think of each other's Christmas gifts. But she, too, has grown up obsessed with her brother's death, which she blames for the disintegration of her family. Left to her own devices for the summer, she resolves to track down and punish Robin's killer, whom she decides, based on the most circumstantial indications, must be Danny Ratliff, a former classmate of Robin's who has sunk into a life of petty crime. As Harriet trails Danny around town (there are shades of Harriet the Spy here), waiting for the right moment to strike, he becomes equally obsessed with her, convinced that she is out to get him for an entirely different reason.