Tempest remains blissfully unaware throughout the novel, despite warnings from people he meets, that Lucio is the earthly incarnation of the Devil. Over the course of the book, his wealth leads to misery. Eventually, when confronted with the true nature of his companion, he renounces evil and returns to society penniless but content with the chance to purify his soul.
Although the plot follows Tempest's fall from grace and redemption, he is in many regards a secondary character to Lucio. Both the title of the work and much of its philosophical content relate to the supreme yearning within Satan to achieve salvation. The book's main contribution to Faustian literature is the introduction of the concept that above all other people it is Satan who most truly believes in the Gospel â and yet he is forbidden to ever partake of it.