[1] The book drew inspiration from the geography of Dante's Inferno and the theology of C S Lewis's The Great Divorce, which is that salvation and entry into paradise, via self-knowledge and repentance, can be achieved by all.

He finds himself in a Djinn-bottle in the Vestibule on the outer edge to Hell; he spends a vast amount of time there, but is released when he finally calls upon God for mercy.

Along the way Allen meets a number of his Californian acquaintances and notable people from history (e.g. Epictetus, Billy the Kid, Jesse James, Bob Ford, L Ron Hubbard, Henry VIII of England, Vlad Tepes, Aimee Semple McPherson, William M. Tweed, Al Capone) and from classical mythology (e.g. Hector, Aeneas, Charon, Minos, Phlegyas, Geryon).

Due to the long time he spent bottled up in the outer vestibule he also meets some people from the future of 1976, such as a Space Shuttle pilot.

The authors said that Inferno was far more successful than they predicted, and they were told that it inspired a resurgence of interest in Dante amongst college students and a new print release of John Ciardi's translation (whose quotes appear in the novel).