Eberstadt’s fifth novel is far more charming than the title suggests: Its subject is not a rodent but a teenager named Celia Bonnet—nicknamed “Rat” by her mother, Vanessa—who lives in France. Rat and Vanessa are “close as sisters, sometimes twins,” but when her mother takes up with an abusive boyfriend, Rat runs away to England to find her estranged father. Although Eberstadt works on a small canvas—nothing flashy here—she deftly captures the vicissitudes of youth and middle age in equal measure.