Hannah Rothschild, a scion of the banking dynasty, wrote her first nonfiction book, “The Baroness,” about the life of her great-aunt Pannonica, a rebel who abandoned her notorious family to become a passionate patron of jazz. That story was complex, unpredictable and enriched by a serious consideration of the human impact of vast wealth.

By contrast, Rothschild’s first novel, “The Improbability of Love,” is an exuberant, uneven satire of consumption and corruption in the London art world. This is fiction aimed at readers who find “Downton Abbey” too bleakly realistic. The cast of caricatures is blessed with deliciously absurd names ranging from Liora van Cuttersman to M. Power Dub-Box — a cliche of a rap star who shows up at the art auction that opens the novel with a posse of writhing, nearly naked women.

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At the heart of the silliness, however, lies a serious question about the value of art in a market that has become a species of commodities trading and a convenient way for unsavory billionaires to bury their wealth and burnish their reputations. Given this cut­throat game that governments and public museums can barely afford to play, a cynic would conclude that there’s no such thing as inherent value: A painting is only worth what someone will pay. “The Improbability of Love” is not quite so cynical, although plenty of its characters are.

The exception is our struggling heroine, Annie, who stumbles across a grubby but entrancing painting in a junk shop and impulsively buys it as a gift for a man she’s been dating. He promptly dumps her, leaving her stuck with what turns out to be a lost masterpiece by an 18th-century rococo painter. This small work of art depicts lovers in a sylvan glade, and apparently it possesses the power to drive its owners and admirers into paroxysms of desire. At several points in the book, the painting itself addresses the reader, expanding the story’s historical reach while stretching our tolerance for whimsy.

Annie, pretty as a picture under her baggy pants and Doc Martens boots, is an outsider to the art world and naive to its machinations. Newly arrived in London with a broken heart, she’s saddled with a mess of an alcoholic mother who is nevertheless very effective at advancing the plot. Annie attracts the attention of a sweet-natured guide at London’s Wallace Collection who helps her sleuth out her painting’s provenance while — surprise! — falling in love. But unfortunately, Annie has just taken a job as the private chef for Britain’s most powerful father-daughter art dealers, and all is not what it seems with the 91-year-old patriarch. He will go to any lengths to cover up his past, in which Annie’s painting plays a crucial role.

Rothschild has so much fun mixing up her colorful characters — like the self-styled Barthomley Chesterfield Fitzroy St. George, Svengali to the nouveaux riches — that the plot is slow to get going and its denouement somewhat slapdash. But as befits a novel by the chair of the National Gallery and a trustee of the Tate, “The Improbability of Love” is enlivened by insider knowledge that’s too juicy to be entirely fictional.