In the 1830s, parts of young America were caught up in the apex of the Second Great Awakening, the mass spiritual enthusiasm that cemented evangelical Protestantism as a hugely influential, even foundational, tenet of American society. Nowhere was this more evident than in western New York, the so-called Burned-Over District, where Finneyite revivals swept up much of the population in the religious movement. This fervor gave rise to new religious sects like Mormonism. It was also fertile ground for millenialists, who felt that good works on Earth would hasten the coming of Christ and his thousand years of peace - this was a driving force behind the reformist movements of the age such as abolitionism, temperance, and women's suffrage. The other approach was millenarianism, which claimed that a cataclysmic millennium was coming, but that only those chosen by God for their purity and holiness would be saved. This led to Utopian societies that set themselves apart from the rest of the world to await the coming of the Messiah.
Into this environment strode Robert Matthias, a charismatic failed carpenter and con man, who convinced followers to join his cult and subject themselves to his absolutist rule. It went about how these things go - the prophet slept with all the women, there was fighting and resentment, financial disarray - essentially a Trump family reunion without the gold toilet bowl. The Kingdom of Matthias eventually clashed with the law (think Branch-Davidians outside Waco, or Jonestown) and collapsed.
The book is a fascinating study of the time period, when Church Street (and later Wall Street) became the most powerful forces in American life and politics. It's also a troubling look at the seductive world of cults that still happen today.