Any Geraldine Brooks novel is a welcome event and “Horse,” a fictionalized biopic of famous American racehorse Lexington, overlaid with a modern story, is a rich treat of measured, intelligent prose. The current-day tale of a museum scientist and black art historian, revolving around mysterious paintings and bones, seems at first to be on the sidelines of the main storyline of Lexington and his slave groom in the 1850s, but the author meticulously braids all the strands together. I could not imagine anything about horse racing to hold interest but somehow Brooks not only renders that world fascinating but illuminates slavery and racism resonating over nearly two centuries. The characters, especially the three core ones and a charismatic rogue, all sparkle, and the author’s prose is seamless and affecting. Horse is an unexpected triumph.