The birth of Siamese twin girls in the town of Spanish Fork, Utah, in 1849 causes quite a stir. Residents flock to the Chatham Ranch to see the babies and offer their condolences for the loss of the mother who did not survive the birth. When the attempted sale of the twins by their father to a passing circus fails, they are kidnapped by circus owner Colonel Phantastic. Young Deputy John Walker is sent to Salt Lake City to retrieve them and is surprised when the twins' sister Zelda joins him on the train. In a whirlwind romance, they are married and together confront the babies' derelict father and the Colonel in their separate pursuits of the infant girls.
The story of Prudence and Chastity covers twenty years and takes them to Alamo, Montana, where they hope to finance their unspoken goal of separation as showgirls and prostitutes. There they are rescued by a fifteen-year-old boy from the Blazing Star when it burns. Sam Shines travels with them to St. Louis, where he is wanted for murder, and on to Chicago for an appointment with a renowned doctor. Their arrival coincides with the Great Chicago Fire, as conflagration continues to define their lives.
The twins are at once beautiful, charming, and fascinating to anyone who sees them. Their influence on the lives of those they hold close is haunting, sometimes tragic, and always unforgettable.