To fully appreciate this literally wonderful book, one must realize that it is only one part of a sprawling saga, the "Argo Mythos", revolving around that legendary ship and those who have sailed on it. Within that saga lies the "Devil Is Dead" trilogy, of which this book (confusingly, of the same name) is but the middle part, its predecessor being "Archipelago" and its successor being "More Than Melchisedech" (which, to further complicate score-keeping, was published in three volumes, named "Tales of Chicago", "Tales of Midnight", and "Argo"). Also part of the Argo Mythos is the novel "Dotty", and--arguably--the "Coscuin" tetralogy (of which the final two books are yet unpublished, though the manuscripts exist).
Finnegan, the chief protagonist, is adapted from the character Finn McCool of Irish legend, and parts of the saga derive from that legendarium; he also, however, partakes to some extent of the nature of Jason, the hero we normally associate with the Argo. Further--though one can read the saga without needing to know this--Lafferty has adopted the Argo itself as symbolic of the Roman Catholic Church, of which Lafferty was--to put it mildly--an ardent adherent.
This novel, the saga, the entirety of Lafferty's work: it is all literary genius of a high order, something the casual reader may miss owing to Lafferty's very down-to-earth writing style, which in many ways is almost conversational in tone. But then, the definition of a professional is someone who makes it all look easy.