For those dismayed by our presidential race, take heart: "The Vanishing Velázquez" is a welcome diversion, a literary page-turner about the ineffability of artistic genius and one man's passion for a painting that drove him from his family and colleagues in England to a hermit's life in New York. Laura Cumming, art critic for the Observer, elegantly weaves a narrative that is equal parts criticism, detective story and pure enchantment.

"The Vanishing Velázquez" is actually about three separate but linked vanishings. Diego Velázquez (1599-1660) was an acclaimed painter in the Spanish court of Philip IV; early in his career, he painted the Prince of Wales (later the doomed monarch Charles I), who was visiting Madrid as a suitor to one of Philip's daughters. The painting was widely admired but soon disappeared from view.

Flash forward to the English town of Reading in 1845, when John Snare, a bookseller and amateur art collector, bid successfully on a dust-filmed portrait attributed to Van Dyck. After he'd cleaned the canvas, Snare was convinced he'd acquired the missing portrait, relying on his own eyeballs rather than reams of documentation: "The art of Velázquez was rare, unfamiliar, obscure. … Prints were precious few and could scarcely convey his mysterious and diaphanous style."

Thrilled by his good fortune, Snare sought out authentication from the experts of the day. Some agreed that the artist was Velázquez; others scoffed at the opinion of a middle-class nobody from the country. Snare used the controversy to gin up attention for his painting, fending off legal challenges that culminated in a lengthy trial in Edinburgh. The jury decided for Snare, but by the time the verdict came down, Snare had vanished — to New York, where for decades he showed his Velázquez to admiring audiences while eking out a living as a bookseller.

He never returned to England, and his prized possession disappeared after his death.

Cumming teases from Snare's story a crucial argument: A zeal for an artist's work, an ability to trust one's own eyes, a response informed by history and shunning small-bore debates — that is the essence of vibrant art criticism. Her own love of the Spaniard is contagious: "Velázquez is able to see the whole world before him in the microcosm of the court, in the faces of servants on the stairs, in the behaviour of children, in the conversation and attitudes of actors and dwarves. He finds a Venus and a Mars in the humble people around him, sees a king as compellingly ordinary. … There is an extraordinary equality to his empathetic gaze."

"The Vanishing Velazquez," by Laura Cumming

Her Velázquez is fundamentally modern, a painter out of time, his brushwork and compositions anticipating Realism and Impressionism, even Picasso, who reinterpreted the masterpiece "Las Meninas."

With "The Vanishing Velázquez," Laura Cumming spins a layered, irresistible tale, one that resonates today.

Hamilton Cain is the author of "This Boy's Faith: Notes From a Southern Baptist Upbringing." He lives in Brooklyn, N.Y.