Smiley is juggling such a giant cast that, even deep into the book, you’re trying to remember who on earth is who. A few people–and horses–do make indelible impressions. There’s a mellow trainer named Farley, who follows “The Tibetan Book of Thoroughbred Training,” and a crooked one named Buddy, who thinks he’s found God. There’s a horse named Limitless who triumphs, and one named Justa Bob who is subjected to indignities that will make you shiver.

Horse racing is all-consuming sport in “Horse Heaven.” Everyone lusts after the Kentucky Derby and the Breeders’ Cup, shouting “that old refrain… I want I want I want.” But because Smiley is constantly channel-surfing between story lines, her novel gets choppy, and even the races don’t quite thrill. The author delivers tender moments (an owner’s wife falling back in love with her husband after a tryst) and tense ones (a horse freaking out on an airplane). Unfortunately, they’re not enough to carry the book. Unless you’re a horse-racing buff, you’re going to struggle to cross the finish line.

Horse HeavenJane Smiley (Knopf) 561 pages. $26